SMD Soldering Guide

1 SMD Soldering Guide Basic Electronics Soldering & Desoldering Guide VERY VERY IMPORTANT: This chapters will expose you to the art of soldering eletronic components on a laptop motherboard with pictures and video illustrations, it is therefore critical that you understand this very concept which forms 95% of chip level repairs This written guide will help beginners and novices to obtain effective results when soldering electronic components. If you have little or no experience of using a soldering iron, then EPE (Everyday Practical Electronics magazine) recommends that you practice your soldering technique on some fresh surplus components and clean stripboard (protoboard), before experimenting with a proper constructional project. This will help you to avoid the risk of disappointment when you start to assemble your first prototypes. If you've never soldered before, then read on! Soldering irons Topics in this section include: Voltage Wattage Temperature Control Soldering Stations Anti Static Protection Bits (Tips) Spare Parts Gas-Powered irons The most fundamental skill needed to assemble any electronic project is that of soldering. It takes some practice to make the perfect joint, but, like riding a bicycle, once 2 learned is never forgotten! The idea is simple: to join electrical parts together to form an electrical connection, using a molten mixture of lead and tin (solder*) with a soldering iron. A large range of soldering irons is available - which one is suitable for you depends on your budget and how serious your interest in electronics is. [*Note: the use of lead in solder is now increasingly prohibited in many countries. "Lead free" solder is now statutory instead.] Electronics catalogues often include a selection of well-known brands of soldering iron. Excellent British-made ones include the universally popular Antex, Adcola and Litesold makes. Other popular brands include those made by Weller and Ungar. A very basic mains electric soldering iron can cost from under £5 (US$ 8), but expect a reasonable model to be approximately £10-£12 (US$ 16 - 20) - though it's possible to spend into three figures on a soldering iron "station" if you're really serious! Check some suppliers' catalogues for some typical types. Certain factors you need to bear in mind include:- Voltage: most irons run from the mains at 240V. However, low voltage types (e.g. 12V or 24V) generally form part of a "soldering station" and are designed to be used with a special controller made by the same manufacturer. Wattage: Typically, they may have a power rating of between 15-25 watts or so, which is fine for most work. A higher wattage does not mean that the iron runs hotter - it simply means that there is more power in reserve for coping with larger joints. This also depends partly on the design of the "bit" (the tip of the iron). Consider a higher wattage iron simply as being more "unstoppable" when it comes to heavier-duty work, because it won't cool down so quickly. Temperature Control: the simplest and cheapest types don't have any form of temperature regulation. Simply plug them in and switch them on! Thermal regulation is "designed in" (by physics, not electronics!): they may be described as "thermally balanced" so that they have some degree of temperature "matching" but their output will otherwise not be controlled. Unregulated irons form an ideal general purpose iron for most users, and they generally cope well with printed circuit board soldering and general interwiring. Most of these "miniature" types of iron will be of little use when attempting to solder large joints (e.g. very large terminals or very thick wires) because the component being soldered will "sink" heat away from the tip of the iron, cooling it down too much. (This is where a higher wattage comes in useful.) A proper temperature-controlled iron will be quite a lot more expensive - retailing at say £40 (US$ 60) or more - and will have some form of built-in thermostatic control, to ensure that the temperature of the bit (the tip of the iron) is maintained at a fixed level (within limits). This is desirable especially during more frequent use, since it helps to ensure that the temperature does not "overshoot" in between times, and also guarantees that the output will be relatively stable. Some irons have a bimetallic strip thermostat built into the handle which gives an audible "click" in use: other types use all-electronic controllers, and some may be adjustable using a screwdriver. 3 Yet more expensive still, soldering stations cost from £70 (US$ 115) upwards (the iron may be sold separately, so you can pick the type you prefer), and consist of a complete bench-top control unit into which a special low-voltage soldering iron is plugged. Some versions might have a built-in digital temperature readout, and will have a control knob to enable you to vary the setting. The temperature could be boosted for soldering larger joints, for example, or for using higher melting-point solders (e.g. silver solder). These are designed for the most discerning users, or for continuous production line/ professional use. The best stations have irons which are well balanced, with comfort-grip handles which remain cool all day. A thermocouple will be built into the tip or shaft, which monitors temperature. Anti-static protection: if you're interested in soldering a lot of static-sensitive parts (e.g. CMOS chips or MOSFET transistors), more advanced and expensive soldering iron stations use static-dissipative materials in their construction to ensure that static does not build up on the iron itself. You may see these listed as "ESD safe" (electrostatic discharge proof). The cheapest irons won't necessarily be ESD-safe but never the less will still probably perform perfectly well in most hobby or educational applications, if you take the usual anti-static precautions when handling the components. The tip would need to be well earthed (grounded) in these circumstances. Bits: it's useful to have a small selection of manufacturer's bits (soldering iron tips) available with different diameters or shapes, which can be changed depending on the type of work in hand. You'll probably find that you become accustomed to, and work best with, a particular shape of tip. Often, tips are iron-coated to preserve their life, or they may be bright-plated instead. Copper tips are seldom seen these days. Spare parts: it's nice to know that spare parts may be available, so if the element blows, you don't need to replace the entire iron. This is especially so with expensive irons. Check through some of the larger mail-order catalogues. You will occasionally see gas-powered soldering irons which use butane rather than the mains electrical supply to operate. They have a catalytic element which, once warmed up, continues to glow hot when gas passes over them. Service engineers use them for working on repairs where there may be no power available, or where a joint is tricky to reach with a normal iron, so they are really for occasional "on the spot" use for quick repairs, rather than for mainstream construction or assembly work. One example is the Maplin PG509, given a full review with photographs here. Another technique is the proprietary "Coldheat" battery powered soldering iron that we reviewed here. There are a number of reasons why this should only be used with extreme care (if at all) on electronic circuitboards. A solder gun is a pistol-shaped iron, typically running at 100W or more, and is completely unsuitable for soldering modern electronic components: they're too hot, heavy and unwieldy for micro-electronics use. Plumbing, maybe..! 4 Soldering irons are best used along with a heat-resistant bench-type holder, so that the hot iron can be safely parked in between use. Soldering stations already have this feature, otherwise a separate soldering iron stand is essential, preferably one with a holder for tipcleaning sponges. Now let's look at how to use soldering irons properly, and how to put things right when a joint goes wrong. How to solder Turning to the actual techniques of soldering, firstly it's best to secure the work somehow so that it doesn't move during soldering and affect your accuracy. In the case of a printed circuit board, various holding frames are fairly popular especially with densely populated boards: the idea is to insert all the parts on one side ("stuffing the board"), hold them in place with a special foam pad to prevent them falling out, turn the board over and then snip off the wires with cutters before making the joints. The frame saves an awful lot of turning the board over and over, especially with large boards. Other parts could be held firm in a modeller's small vice, for example. Solder joints may need to possess some degree of mechanical strength in some cases, especially with wires soldered to, say, potentiometer or switch tags, and this means that the wire should be looped through the tag and secured before solder is applied. The down side is that it is more difficult to de-solder the joint (see later) and remove the wire afterwards, if required. Otherwise, in the case of an ordinary circuit board, components' wires are bent to fit through the board, inserted flush against the board's surface, splayed outwards a little so that the part grips the board, and then soldered. In my view - opinions vary - it's generally better to snip the surplus wires leads off first, to make the joint more accessible and avoid applying a mechanical shock to the p.c.b. joint. However, in the case of semiconductors, I often tend to leave the snipping until after the joint has been made, since the excess wire will help to sink away some of the heat from the semiconductor junction. Integrated circuits can either be soldered directly into place if you are confident enough, or better, use a dual-in-line socket to prevent heat damage. The chip can then be swapped out if needed. Parts which become hot in operation (e.g. some resistors), are raised above the board slightly to allow air to circulate. Some components, especially large electrolytic capacitors, may require a mounting clip to be screwed down to the board first, otherwise the part may eventually break off due to vibration. The perfectly soldered joint will be nice and shiny looking, and will prove reliable in service. I would say that: 5  cleanliness  temperature  time  adequate solder coverage are the key factors affecting the quality of the joint. A little effort spent now in soldering the perfect joint may save you - or somebody else - a considerable amount of time in troubleshooting a defective joint in the future. The basic principles are as follows. Really Clean Firstly, and without exception, all parts - including the iron tip itself - must be clean and free from contamination. Solder just will not "take" to dirty parts! Old components or copper board can be notoriously difficult to solder, because of the layer of oxidation which builds up on the surface of the leads. This repels the molten solder and this will soon be evident because the solder will "bead" into globules, going everywhere except where you need it. Dirt is the enemy of a good quality soldered joint! Hence, it is an absolute necessity to ensure that parts are free from grease, oxidation and other contamination. In the case of old resistors or capacitors, for example, where the leads have started to oxidise, use a small hand-held file or perhaps scrape a knife blade or rub a fine emery cloth over them to reveal fresh metal underneath. Stripboard and copper printed circuit board will generally oxidise after a few months, especially if it has been fingerprinted, and the copper strips can be cleaned using an abrasive rubber block, like an aggressive eraser, to reveal fresh shiny copper underneath. Also available is a fibre-glass filament brush, which is used propelling-pencil-like to remove any surface contamination. These tend to produce tiny particles which are highly irritating to skin, so avoid accidental contact with any debris. Afterwards, a wipe with a rag soaked in cleaning solvent will remove most grease marks and fingerprints. After preparing the surfaces, avoid touching the parts afterwards if at all possible. Another side effect of having dirty surfaces is the tendency for people to want to apply more heat in an attempt to "force the solder to take". This will often do more harm than good because it may not be possible to burn off any contaminants anyway, and the component may be overheated. In the case of semiconductors, temperature is quite critical and they may be harmed by applying such excessive heat. Before using the iron to make a joint, it should be "tinned" (coated with solder) by applying a few millimetres of solder, then wiped on a damp sponge preparing it for use: you should always do this immediately with a new bit, anyway. Personally, I always reapply a very small amount of solder again, mainly to improve the thermal contact between the iron and the joint, so that the solder will flow more quickly and easily. It's sometimes better to tin larger parts as well before making the joint itself, but it isn't generally necessary with p.c.b. work. (All EPE printed circuit boards are "roller-tinned" to preserve their quality and to help with soldering.) A worthwhile product is Weller's Tip 6 Tinner & Cleaner, a small 15 gram tinlet of paste onto which you dab a hot iron - the product cleans and tins the iron ready for use. An equivalent is Adcola Tip-Save. Normal electronics grade solder is now "lead free" and typically contains Sn 97 Ag 2.5 Cu 0.5 (i.e. 97% tin, 2.5% silver and 0.5% copper). It already contains cores of "flux" which helps the molten solder to flow more easily over the joint. Flux removes oxides which arise during heating, and is seen as a brown fluid bubbling away on the joint. The use of separate acid flux paste (e.g. as used by plumbers) should NEVER be necessary in normal electronics applications because electronics-grade solder already contains the correct grade of flux! Other solders are available for specialist work, including aluminium and silver-solder. Different solder diameters are produced, too; 20-22 SWG (19-21 AWG) is 0.91-0.71mm diameter and is fine for most work. Choose 18 SWG (16 AWG) for larger joints requiring more solder. Temperature Another step to successful soldering is to ensure that the temperature of all the parts is raised to roughly the same level before applying solder. Imagine, for instance, trying to solder a resistor into place on a printed circuit board: it's far better to heat both the copper p.c.b. and the resistor lead at the same time before applying solder, so that the solder will flow much more readily over the joint. Heating one part but not the other is far less satisfactory joint, so strive to ensure that the iron is in contact with all the components first, before touching the solder to it. The melting point of most solder is in the region of 188°C (370°F) and the iron tip temperature is typically 330-350°C (626°-662°F). The latest lead-free solders typically require a higher temperature. Now is the time Next, the joint should be heated with the bit for just the right amount of time - during which a short length of solder is applied to the joint. Do not use the iron to carry molten solder over to the joint! Excessive time will damage the component and perhaps the circuit board copper foil too! Heat the joint with the tip of the iron, then continue heating whilst applying solder, then remove the iron and allow the joint to cool. This should take only a few seconds, with experience. The heating period depends on the temperature of your iron and size of the joint - and larger parts need more heat than smaller ones - but some parts (semiconductor diodes, transistors and i.c.s), are sensitive to heat and should not be heated for more than a few seconds. Novices sometimes buy a small clip-on heatshunt, which resembles a pair of aluminium tweezers. In the case of, say, a transistor, the shunt is attached to one of the leads near to the transistor's body. Any excess heat then diverts up the heat shunt instead of into the transistor junction, thereby saving the device from over-heating. Beginners find them reassuring until they've gained more experience. Solder Coverage The final key to a successful solder joint is to apply an appropriate amount of solder. Too much solder is an unnecessary waste and may cause short circuits with adjacent joints. 7 Too little and it may not support the component properly, or may not fully form a working joint. How much to apply, only really comes with practice. A few millimetres only, is enough for an "average" p.c.b. joint, (if there is such a thing). Desoldering methods A soldered joint which is improperly made will be electrically "noisy", unreliable and is likely to get worse in time. It may even not have made any electrical connection at all, or could work initially and then cause the equipment to fail at a later date! It can be hard to judge the quality of a solder joint purely by appearances, because you cannot say how the joint actually formed on the inside, but by following the guidelines there is no reason why you should not obtain perfect results. A joint which is poorly formed is often called a "dry joint". Usually it results from dirt or grease preventing the solder from melting onto the parts properly, and is often noticeable because of the tendency of the solder not to "spread" but to form beads or globules instead, perhaps partially. Alternatively, if it seems to take an inordinately long time for the solder to spread, this is another sign of possible dirt and that the joint may potentially be a dry one. There will undoubtedly come a time when you need to remove the solder from a joint: possibly to replace a faulty component or fix a dry joint. The usual way is to use a desoldering pump or vacuum pump which works like a small spring-loaded bicycle pump, only in reverse! (More demanding users using CMOS devices might need a pump which is ESD safe.) A spring-loaded plunger is released at the push of a button and the molten solder is then drawn up into the pump. It may take one or two attempts to clean up a joint this way, but a small desoldering pump is an invaluable tool especially for p.c.b. work. Sometimes, it's effective to actually add more solder and then desolder the whole lot with a pump, if the solder is particularly awkward to remove. Care is needed, though, to ensure that the boards and parts are not damaged by excessive heat; the pumps themselves have a P.T.F.E. nozzle which is heat proof but may need replacing occasionally. An excellent alternative to a pump is to use desoldering braid, including the famous American "Soder-Wick" (sic) or Adcola "TISA-Wick" which are packaged in small dispenser reels. This product is a specially treated fine copper braid which draws molten 8 solder up into the braid where it solidifies. The best way is to use the tip of the hot iron to press a short length of braid down onto the joint to be de-soldered. The iron will subsequently melt the solder, which will be drawn up into the braid. Take extreme care to ensure that you don't allow the solder to cool with the braid adhering to the work, or you run the risk of damaging p.c.b. copper tracks when you attempt to pull the braid off the joint. See my photo gallery for more details. I recommend buying a small reel of de-soldering braid, especially for larger or difficult joints which would take several attempts with a pump. It is surprisingly effective, especially on difficult joints where a desoldering pump may prove a struggle. Here's a summary of how to make the perfect solder joint. 1. All parts must be clean and free from dirt and grease. 2. Try to secure the work firmly. 3. "Tin" the iron tip with a small amount of solder. Do this immediately, with new tips being used for the first time. 4. Clean the tip of the hot soldering iron on a damp sponge. 5. Many people then add a tiny amount of fresh solder to the cleansed tip. 6. Heat all parts of the joint with the iron for under a second or so. 7. Continue heating, then apply sufficient solder only, to form an adequate joint. 8. Remove and return the iron safely to its stand. 9. It only takes two or three seconds at most, to solder the average p.c.b. joint. 10. Do not move parts until the solder has cooled. Troubleshooting Guide  Solder won't "take" - grease or dirt present - desolder and clean up the parts. Or, material may not be suitable for soldering with lead/tin solder (eg aluminium).  Joint is crystalline or grainy-looking - has been moved before being allowed to cool, or joint was not heated adequately - too small an iron/ too large a joint.  Solder joint forms a "spike" - probably overheated, burning away the flux. First Aid If you are unlucky enough to receive burns which require treatment, here's what to do :- 1. Immediately cool the affected area with cold running water for several minutes. 2. Remove any rings etc. before swelling starts. 3. Apply a sterile dressing to protect against infection. 4. Do not apply lotions, ointments etc., nor prick any blisters which form later. 5. Seek professional medical advice where necessary. 9 First a few safety precautions:  Never touch the element or tip of the soldering iron. They are very hot (about 400°C) and will give you a nasty burn.  Take great care to avoid touching the mains flex with the tip of the iron. The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately if touched by a hot iron and there is a serious risk of burns and electric shock.  Always return the soldering iron to its stand when not in use. Never put it down on your workbench, even for a moment!  Work in a well-ventilated area. The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by keeping you head to the side of, not above, your work.  Wash your hands after using solder. Solder contains lead which is a poisonous metal. If you are unlucky (or careless!) enough to burn yourself please read the First Aid section. Preparing the soldering iron:  Place the soldering iron in its stand and plug in. The iron will take a few minutes to reach its operating temperature of about 400°C.  Dampen the sponge in the stand. The best way to do this is to lift it out the stand and hold it under a cold tap for a moment, then squeeze to remove excess water. It should be damp, not dripping wet.  Wait a few minutes for the soldering iron to warm up. You can check if it is ready by trying to melt a little solder on the tip.  Wipe the tip of the iron on the damp sponge. This will clean the tip.  Melt a little solder on the tip of the iron. This is called 'tinning' and it will help the heat to flow from the iron's tip to the joint. It only needs to be done when you plug in the iron, and occasionally while soldering if you need to wipe the tip clean on the sponge. You are now ready to start soldering: 10  Hold the soldering iron like a pen, near the base of the handle. Imagine you are going to write your name! Remember to never touch the hot element or tip.  Touch the soldering iron onto the joint to be made. Make sure it touches both the component lead and the track. Hold the tip there for a few seconds and...  Feed a little solder onto the joint. It should flow smoothly onto the lead and track to form a volcano shape as shown in the diagram. Apply the solder to the joint, not the iron.  Remove the solder, then the iron, while keeping the joint still. Allow the joint a few seconds to cool before you move the circuit board.  Inspect the joint closely. It should look shiny and have a 'volcano' shape. If not, you will need to reheat it and feed in a little more solder. This time ensure that both the lead and track are heated fully before applying solder. If you are unlucky (or careless!) enough to burn yourself please read the First Aid section. Using a heat sink Some components, such as transistors, can be damaged by heat when soldering so if you are not an expert it is wise to use a heat sink clipped to the lead between the joint and the component body. You can buy a special tool, but a standard crocodile clip works just as well and is cheaper. Soldering Advice for Components It is very tempting to start soldering components onto the circuit board straight away, but please take time to identify all the parts first. You are much less likely to make a mistake if you do this! Crocodile clip Rapid Electronics 11 1. Stick all the components onto a sheet of paper using sticky tape. 2. Identify each component and write its name or value beside it. 3. Add the code (R1, R2, C1 etc.) if necessary. Many projects from books and magazines label the components with codes (R1, R2, C1, D1 etc.) and you should use the project's parts list to find these codes if they are given. 4. Resistor values can be found using the resistor colour code 5. Capacitor values can be difficult to find because there are many types with different labelling systems! Some components require special care when soldering. Many must be placed the correct way round and a few are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together with other advice which may be useful when soldering. For most projects it is best to put the components onto the board in the order given below: Components Pictures Reminders and Warnings 1 IC Holders (DIL sockets) Connect the correct way round by making sure the notch is at the correct end. Do NOT put the ICs (chips) in yet. 2 Resistors No special precautions are needed with resistors. 3 Small value capacitors (usually less than 1μF) These may be connected either way round. Take care with polystyrene capacitors because they are easily damaged by heat. 4 Electrolytic capacitors (1μF and greater) Connect the correct way round. They will be marked with a + or - near one lead. 5 Diodes Connect the correct way round. Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat. 6 LEDs Connect the correct way round. The diagram may be labelled a or + for anode and k or - 12 for cathode; yes, it really is k, not c, for cathode! The cathode is the short lead and there may be a slight flat on the body of round LEDs. 7 Transistors Connect the correct way round. Transistors have 3 'legs' (leads) so extra care is needed to ensure the connections are correct. Easily damaged by heat. 8 Wire Links between points on the circuit board. single core wire Use single core wire, this is one solid wire which is plastic-coated. If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is stiffer. 9 Battery clips, buzzers and other parts with their own wires Connect the correct way round. 10 Wires to parts off the circuit board, including switches, relays, variable resistors and loudspeakers. stranded wire You should use stranded wire which is flexible and plasticcoated. Do not use single core wire because this will break when it is repeatedly flexed. 11 ICs (chips) Connect the correct way round. Many ICs are static sensitive. Leave ICs in their antistatic packaging until you need them, then earth your hands by touching a metal water pipe or window frame before touching the ICs. Carefully insert ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb. 13 What is solder? Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200°C. Coating a surface with solder is called 'tinning' because of the tin content of solder. Lead is poisonous and you should always wash your hands after using solder. Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip. Without flux most joints would fail because metals quickly oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal surface. The best size of solder for electronics is 22swg (swg = standard wire gauge). Desoldering At some stage you will probably need to desolder a joint to remove or re-position a wire or component. There are two ways to remove the solder: 1. With a desoldering pump (solder sucker)  Set the pump by pushing the spring-loaded plunger down until it locks.  Apply both the pump nozzle and the tip of your soldering iron to the joint.  Wait a second or two for the solder to melt.  Then press the button on the pump to release the plunger and suck the molten solder into the tool.  Repeat if necessary to remove as much solder as possible. Reels of solder Rapid Electronics Using a desoldering pump (solder sucker) 14  The pump will need emptying occasionally by unscrewing the nozzle. 2. With solder remover wick (copper braid)  Apply both the end of the wick and the tip of your soldering iron to the joint.  As the solder melts most of it will flow onto the wick, away from the joint.  Remove the wick first, then the soldering iron.  Cut off and discard the end of the wick coated with solder. After removing most of the solder from the joint(s) you may be able to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself. First Aid for Burns Most burns from soldering are likely to be minor and treatment is simple:  Immediately cool the affected area under gently running cold water. Keep the burn in the cold water for at least 5 minutes (15 minutes is recommended). If ice is readily available this can be helpful too, but do not delay the initial cooling with cold water.  Do not apply any creams or ointments. The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to protect the area from dirt.  Seek medical attention if the burn covers an area bigger than your hand. To reduce the risk of burns:  Always return your soldering iron to its stand immediately after use.  Allow joints and components a minute or so to cool down before you touch them.  Never touch the element or tip of a soldering iron unless you are certain it is cold. Solder remover wick 15 SMD Soldering Purpose The purpose of this guide is to introduce SMD (Surface Mount Device) hand soldering. The guide is organized into different methods. Each method is used specifically for a group of SMD components. A simplified list is included with each method to identify which types of SMD components are for the appropriate method. SMD Hand Soldering Methods  Method 1 - Pin by pin Used for : two pin components (0805 caps & res), pitches >= 0.0315" in Small Outline Package, (T)QFP and SOT (Mini 3P).  Method 2 - Flood and suck Used for : pitches <= 0.0315" in Small Outline Package and (T)QFP  Method 3 - Solder paste Used for BGA, MLF / MLA packages; where the pins are underneath the part and inaccessible.  Desoldering SMD Special methods for desoldering without the need for special soldering iron tips. Method 1 - Pin by pin Used for : Diodes, Capacitors and Resistors in sizes like 0603, 0805, 1206, 1210, 1812, 1825, 3216, 3528, 6032, and 7343. Small Outline Packages and QFP with pitches >= 0.0315". Like SO.050" and SO.80mm (0.0315") SOT packages like SOT223, SOT23, SOT143, SOT89, Mini-5P, and Mini-6P. 0805 Capacitor example : 16 Step 1 Place a small amount of solder on one of the two pads. Aprox. 0.5mm in height. Step 2 Grab the 805 part with very fine tweezers. Bring the part overtop of the pads, slight to one side so that the part can sit flat against the PCB. Heat the pad already with solder and slide the part onto the pad so that it is centered between the pads. Remove heat. Step 3 Put a small force down on the part and reheat the one pad to guarantee that the parts is flat against the PCB. Step 4 Solder the other side of the part. The solderings should not look like "round ball" on either side of the parts. If this is the cast, there is too much solder being appied to the joint. A properly soldered joint should have a curved line from the end of the pad to the top of the part as shown in the pictures. 17 Small Outline Package - SO.050 example : Step 1 Place a small amount of solder on one of the conner pads. Aprox. 0.5mm in height. Step 2 Grab the 14 pin SOP part with very fine tweezers. Bring the part overtop of the pads, sit the part on top of the pads. Heat the pad with solder and adjust the part so that it lines up with the pads. Besure the part is flat and aligned, then remove the heat. Step 3 Now solder the rest of the pins, oneat- a-time. Use a chise tpye tip (1/32" wide). Contact the pin and pad at the same time with the conrner of the tip. Do not use the end of the tip or solder will flow from pin to pin. Start with the pin at the adjacent corner to the pin already started. 18 SOT23 example : Step 1 Place a small amount of solder on one of the three pads. Aprox. 0.5mm in height. Step 2 Grab the SOT23 part with very fine tweezers. Bring the part overtop of the pads, slight to one side so that the part can sit flat against the PCB. Heat the pad already with solder and slide the part onto the pad so that it is centered between the three pads. Remove heat. Step 3 Put a small force down on the part and reheat the one pad to guarantee that the parts is flat against the PCB. Step 4 Now solder the other two pins, one-at-atime. Use a chise tpye tip (1/32" wide). Contact the pin and pad at the same time with the conrner of the tip. Do not use the end of the tip or solder will flow from pin to pin. Method 2 - Flood and suck 19 Used for : Small Outline packages and (T)QFP with pitches <= 0.0315". Like SO.025", SO.80mm (0.0315"), SO.65mm (0.0256"), SO.50mm, SO.40mm, and SO.30mm. Small Outline Package - SO.65mm example : Step 1 Place a small amount of solder on one of the conner pads. Aprox. 0.5mm in height. Step 2 Grab the 8 pin SOP part with very fine tweezers. Bring the part overtop of the pads, sit the part on top of the pads. Heat the pad with solder and adjust the part so that it lines up with the pads. Besure the part is flat and aligned, then remove the heat. Step 3 Now flood the opposite row of pins with solder so that there is one continuous flow across the pins as shown. Continue by flooding the other row of pins. Try to keep the solder across the pins as even as possible. 20 Step 4 Using the iron, (or a heated sucker) heat one end of the pins until the solder is melted 2-3 pins in length from the end. Quickly remove the iron and using a solder sucker, suck the excess solder from between the pins. Heat the solder on the next 2-3 pins and do the same until the other end is reached. Do the same on the other side of the chip. Finally inspect the pins to check if any solder is left between them. If there is, re-apply solder between the pins and re-suck. This method works because sucking only removes the solder between the pins and not the solder between the pad and pin. (Thin) Quad Flat Package - SO.80mm example : Step 1 Place a small amount of solder on one of the conner pads. Aprox. 0.5mm in height. 21 Step 2 Grab the 32 pin TQFP part with very fine tweezers. Bring the part overtop of the pads, sit the part on top of the pads. Heat the pad with solder and adjust the part so that it lines up with the pads. Besure the part is flat and aligned on all four sides, then remove the heat. Step 3 Now flood the opposite row of pins with solder so that there is one continuous flow across the pins as shown. Continue by flooding the other three rows of pins. Try to keep the solder across the pins as even as possible. Step 4 Using the iron, (or a heated sucker) heat an end of a row until the solder is melted 2-3 pins in length from the end. Quickly remove the iron and using a solder sucker, suck the excess solder from between the pins. Heat the solder on the next 2-3 pins and do the same until the other end is reached. Do the same on the other three sides of the chip. Finally inspect the pins to check if any solder is left between them. If there is, re-apply solder between 22 the pins and re-suck. This method works because sucking only removes the solder between the pins and not the solder between the pad and pin. Method 3 - Solder paste Used for : Used for BGA, MLF / MLA packages; where the pins are underneath the part and inaccessible. Example : To use this method you will need a head gun or a PCB oven. The following instructions are for a heat gun only. Mount the circuit board in a vise that will not burn when heated. It is recommended that the BGA, MLF / MLA parts be soldered to the PCB first in order not to disturb the soldering of the other regular components. If this is not possible then tin foil can be used to shield the regular components. Step 1 Set the part on the board and line it up as it would be soldered. Take note and or mark the PCB so that you will be able to correctly place the part when heating. Step 2 Spread a thin layer of solder paste across the PCB on the pad area for the BGA, MLF / MLA part. The thickness of the solder paste should be thin enough so that the PCB and pads should be semi-visible. The amount is learned by trail and error and experience. 23 Step 3 Plac e the BG A, MLF / ML A part on the PCB and align. Use needle-nose pliers to hold the part in place while heating. Make sure the pliers are not bare metal or they will get too hot to handle when heating. Using the heat gun, apply heat to the part by holding the heat gun 8cm ( 3") away from the board. Step 4 Keep heating until the solder paste has melted into solder all the way around the part. (Should take 20 - 40 seconds) Be sure that the part is aligned and remove the heat. Blow on the part to harden the solder. Inspect around the edges of the part for solder bridges from pad to pad. If there are bridges you will need to reheat the part, remove it, suck the solder from the pads and the part, and repeat the procedure with less solder paste. Desoldering SMD De-soldering SMD components without special soldering iron tips involves creativity. In most cases the SMD component is destroyed. Try to find the proper tip / tool to de-solder before trying the following examples. 24 0805 Capacitor / Resistor de-soldering : Two pin SMD component, such as a 0805 chip capacitor or resistor, is the easiest to de-solder with a regular soldering iron tip. Simply heat one side until the solder is melted, then quickly move to the other side until the solder is melted. Keep alternating between sides. This will build up heat on each side and the part will slide off the pads in 5 - 10 seconds. Small Outline Package - SO.050 example : Step 1 Flood the each row of pins with solder so that there is one continuous flow across the pins as shown. Try to keep the solder across the pins as even as possible. Get a small screwdriver ready to insert under the part. Step 2 Heat one side and move the iron back and forth until the whole row of pins is melted. Insert the screwdriver under that side and pry up until the pins are off the PCB and out of the solder. Step 3 Suck any extra solder that is left between the pads and the part. 25 Step 4 Grip the part with needle-nose pliers. Heat the other side in the same manner and when the whole row is melted remove the part. Step 5 Suck the solder off the pads ready for the new part. BGA, MLF / MLA de-soldering : Cover the PCB in tin foil except for the BGA, MLF / MLA part and the area around it. Heat the part / PCB 8cm ( 3") away with a heat gun. Try heating both the top and bottom side of the PCB. Keep side pressure on the part with fine point needle-node pliers so it will slide off when the solder melts. Surface Mount Soldering Tutorials It's Not That Bad! More and more ICs come in surface mount packages only these days. And I can't tell you how many times I've heard someone say 'Well I can't solder that because it's SMD'. They're wrong! You can solder anything. That's right, anything from your own dorm-cellroom. 26 That's 0.5mm from pin to pin! 50 pin connector for the GM862. You too can solder this! This tutorial will show you just how to solder crazy things like this connector, leadless ICs, etc. There are a very few tools that are required and a handful that are recommended but you'll be able to solder:  SOT23  TQFP  QFN  Even BGA!  And all the others The tools you absolutely must have: 1. $50+ soldering iron 2. Solder wick 3. Solder (leaded is always easier to work with, but here at SFE we use lead-free) That's it. That's all you need. But how can this be? The process of soldering very tight pitch components or even the larger SMD 1206 components just takes practice, a good iron, and some solder wick. Here is a list of tools I recommend: 1. Wire wrap wire (for 'jumper' wire fixes) 27 2. Wire strippers (adjustable down to 30AWG) 3. Hemostatstweezers will also work) 4. Hot-air rework station ($200 will do it) 5. Monocle (I haven't used one, but others have recommended it to me) 6. Scalpel>green wire fixes) Getting chip X onto board Y First, start by getting some SMD device you'd like to solder. 0603 sized components are easy with a little practice. SOT23 packages are relatively large and are common with voltage regulators. SOIC packages are also a really good place to start as well because the pitch is large and the connections are easy to inspect. 28 Here is the board we are going to demo on. It's a very simple 3.3V Lassen iQ GPS serial to RS232 serial breakout board. We will show how to solder the MAX3232 SOIC 16 IC. A shiny tip is a happy tip. No really. ALWAYS clean your tip. Every time you pull the iron out of the holding stand, swipe it quick on the WET sponge. Get off your ass and wet the sponge before you start. If you don't the iron won't heat correctly and the tip will be toast in a day. A small solder tip is recommended but not required. The important thing about your iron is not getting some microscopic tip, but how evenly the heating is. A soldering iron that does not have a temperature control is not acceptable. That $10 iron that you got in your freshman engineering kit is completely worthless. However, you do not need to spend more than ~$80 for a good iron these days. I touched a $500 Metcal once, but they're really overkill for 99% of soldering. Get a good, variable temperature iron from anyone who will also sell you replacement tips. Tips wear out, and you'll be really mad if you've got a perfectly good iron but no where to get a $10 replacement tip. 29 There is no magic here. Add solder to the first pad on the footprint making it dome a bit. 30 Now take your package with hemostats in your off-hand. Heat the domed pad with the soldering iron, liquefying the solder on that one pad. 31 Slide the component into place and you heat the domed pad. You'll need to orient the package so that the other pins line up with their respective pads. 32 Here's my first attempt at soldering. I haven't soldered in about a year so I'm a bit rusty. I accidentally domed two pads. When I tacked the chip down, I didn't seat it all the way. Make sure the IC and as flat against the PCB as possible. This will help prevent open disconnects (nearly as bad as a jumper and more difficult to detect). 33 This is the second attempt, IC is flat against the PCB, but now you see the theta is tweaked a bit. Could you solder the IC successfully with this placement? Yes, of course. But as the packages get larger and the pin counts go up, your alignment has to improve as well. Do the best you can with 2 to 3 heat-reheat alignments. 34 Nice and straight. Once the package is aligned, remove the soldering iron from the pad holding the component still (applying a little downward pressure helps). If the pad solidifies and the package alignment is wonky, just re-heat the pad, re-align, hold still, and remove the iron. The initial heat-slide-align process takes a fraction of a second with a little practice. Do note: heating and reheating pads stresses them. It's totally normal for a beginner to 'lift' a pad on your first or second soldering project. 'Lifting' a pad is bad thing. It occurs because the exposed metal surface pulls away from the FR4 PCB material underneath (also called delaminating). Basically the pad and trace are toast, but you can always green wire from the pin to a local via or same-net pin. More on that later. 35 Okay, so once you've got the component soldered to the single pad and aligned, you can then solder to all the other pins. Start on the opposite side of the package away from your anchoring pad. If you start soldering from the anchor pin, you run the risk of reheating the pad and the component will slide around or stick to your iron tip. Tip: I usually like to have a small puddle of solder on the tip before I start soldering so that the heat transfers easily from the point of the tip to the pin/pad you are soldering to. 36 Once you've added solder to a few pins, you'll probably notice the solder can fill in between pins. This is ok. Solder that is connecting two (or more) pins together is called a jumper. Most of the time, this is bad and can cause problems. To remove solder between pins, you can use solder wick. Solder wick is composed of small copper strands braided together with some chemical additives that have been formulated and manufactured in such a way to attract the solder. Basically, you're playing with surface tension. With a little practice you can take a ball of solder on the end of your iron and run up and down an IC without ever creating a jumper - using only the surface tension of the solder ball and the incoming solder/flux to move things where they really should be. 37 Since this is nearly impossible for, well, everyone, companies have created solder wick. We like size #2. We buy it in 50' rolls but we also use it like it's Kleenex so 25' should be sufficient for multiple small projects of your own. 38 If you've never played with solder wick before, take the end of your iron and add some solder to the tip - get a good blob. Now take the tip and touch it to the solder wick. After a few seconds, the solder wick will heat up and the solder will migrate from the tip to the wick, spreading quickly - hence 'wicking' away the solder. Solder wick can't be re-used to my knowledge. Once the wick turns silver, you cut off the offending bit and throw it away. Well, try anyway. I usually cut off a 1" hardened piece that goes skittering off behind my desk or onto the carpet. Once you start using solder wick, you'll find bits hidden all around for years to come... But you've got to have it! 39 Now let's see what wick can do for us. If you're Mr. Fancy Pants and don't already have a jumper on your IC, make one - jumper two pins together. For the humans in the group that already have a few jumpers, take the end of wick in your bad hand. You'll want to hold 2-3 inches back from the operation because copper loves to transmit heat! I like to use clean, virgin wick so cut off anything that's already been used. Clean your iron tip and add just a smidgen of solder to the end of your tip (this will aid in heat transfer between the parts). 40 Place the wick length-wise over the two jumpered pins and push the wick down with the side of the iron-tip. Quick note: the very tip of the iron (such as the last 1/10th of the iron shown above) is not as useful as the length of the shiny area. Whenever possible, use the side of the tip rather than the point. You'll find that it is much easier to use and transmit heat with. 41 After a split second, the wick should come up to temperature and the solder on the iron and the solder in the jumper should wick into the copper braid! Now, keeping the iron touching the wick, move the wick away from the part. This entire process should take 1, maybe 2 seconds. Don't get crazy with the heating and re-heating or else you'll stress the pad and the IC. If you're just starting out, you'll probably pull the iron away first. Guess what happens? The wick solders itself to the pins. Just be cool. You've got a very strong metal to metal weld. If you go pulling on the wick you'll tear all sorts of things apart. Instead of pulling like a mad-man, add a bit of solder to your iron tip, apply the tip to the wick, and you'll see everything become molten again. Now remove the iron and wick together and you'll be ok! But wait! When I wick away solder, won't that remove solder that connects the pin to the pad? Effectively removing the good connection? No actually. Back to the surface tension thing, solder wick is not strong enough to sneak solder out from under a pin and pad, only from solder that is floating without a pad to adhere to. This wicking process removes only solder jumpers or bad solder. Good solder connections are left in place. Practice practice practice. It's not hard, it just gets easier with time. Some fun tricks: 1) If you've got a jumper or part with solder hiding in a hard place to reach, add more 42 solder! Adding solder to a jumper causes more flux to be added which helps heat flow. If you've got a bit of solder in a hard to reach spot, adding molten solder can be the microscopic hand that sneaks in, heats up the problem bit, and then you've got a much larger bit that can be wicked away. 2) Smash and grab. If you've got a large number of pins to solder on a tight pitch SMD part (think 50-pin molex connector for the GM862), don't fret. Follow the same steps of adding a dome to the anchor pad, lining up and tacking the anchor pin. Now instead of trying to solder each pin, add solder and heat to groups of pins. Don't worry about jumpers, concentrate on getting proper solder on each pin/pad interface. If you don't properly heat each junction, cold joints and intermittent connections may occur later! 43 Once you've got the entire thing sufficiently jumpered, you go back with wick and carefully wick the extra solder away. 44 No microscope, no special tools required! That's it! No magic tricks. Just a good iron, solder wick, and some practice. But what do you do when things get really screwed up? Continue on SMD Soldering Guide Part II