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So you think you can SOLDER? by Nicholas Vinen It’s a critical skill for electronics professionals and hobbyists but many of us have minimal or no formal training in soldering. To find out what we could learn, I attended an IPC soldering training and certification course which is suitable for beginners through to experienced professionals. I learned more than I expected about soldering, rework and PCB repair and there were some surprises too. I f you’re going to build or repair any electronic gear and expect it to last (especially in abusive environments such as marine or automotive), you will need good soldering skills. Bad solder joints are a major cause of failures in both commercial equipment and kits. We’ve met kit constructors who have gone to the trouble of building a PCB, spent time trouble-shooting it and eventually gave up when the problem was simply a few incomplete or unreliable joints. To make matters worse, these days many new ICs come only in surfacemount packages; in some cases your only choice is a fine-pitch or even leadless IC. This means that some projects inevitably require more advanced soldering skills. Many potential constructors feel daunted taking these on but with a little practice and the right tools, it isn’t too difficult. This learning curve is so much less steep if you have guidance from an experienced technician to learn the tricks which make it easy to solder these more difficult devices. These are exactly the sort of skills you will We spent much of our time at the well-stocked workbenches, practising our technique using the supplied PCBs, parts and consumables. However we also watched some videos, slide shows, live demonstrations and had numerous discussions about soldering theory and techniques. IPC Certified Trainer Andrew Brown guided us through the course, checked our work and gave constructive feedback based on the results. 22  Silicon Chip siliconchip.com.au Day three and with our PCBs complete and working, we practiced terminating wire onto various kinds of PCB terminals. These wires were then soldered to the board as a way to keep them all together. More experienced attendees who finished tasks early were able to try different techniques or ask questions. One unusual tool seen here is a timberhandled hog-bristle brush, used for cleaning PCBs and parts due to the fact that it doesn’t generate static electricity. pick up attending a soldering training course such as the one described here. I was invited to attend a 3-day course called “IPC-7711/7721 Rework/ Repair Modification”. IPC is an international organisation and their name originally stood for the “Institute for Printed Circuits”. They now go by the name “Association Connecting Electronics Industries” but still use the widely-recognised initials IPC. The IPC produces global standards for PCB design, manufacturing and electronics assembly, including soldering. This training was provided by an IPC Certified Trainer from Chemtools Pty Ltd, at their office in St Marys, western Sydney. This particular course included removing and replacing through-hole, surface-mount components on a PCB, pad and track repair, PCB laminate repair, wire splicing and conformal coating. However, the exact mix of subjects varies a little, depending on the requirements of the attendees. I learned a lot at this course but it was also very enjoyable. The group was small, with a total of nine attendees which is typical. This gives a lot of opportunity to ask questions. It also means personal attention and feedback from the trainer. siliconchip.com.au The other eight attendees ranged from a complete beginner through to experienced service and manufacturing personnel (yes, there are still electronics manufacturers in Australia!). By the end of the course, the beginner had successfully soldered a wide variety of through-hole and surfacemount devices and went away a lot more capable and confident than just three days earlier. Some surprises He obviously got a lot out of the course but so did many of the more experienced members of the group, myself included. One of the aspects I especially liked was the opportunity to try various different techniques for doing the same job. For example, one part of the course involved soldering a very fine pitched (0.4mm lead spacing) Thin Quad Flat Pack (TQFP) IC. The instructor explained three different methods to solder this part, demonstrated one and stated that we could use whichever we wanted. I elected to use a method which I had not tried before, which involved placing a thin layer of solder on the pads, locating the IC accurately over them, applying flux and then re-heating the pads (and component leads) with a standard iron so the solder ‘reflows’ onto the device leads. This is a similar approach to one of the most common commercial soldering methods (infrared reflow) but without needing any special gear. It was gratifying that this not only worked but as the instructor promised, made a series of near-perfect joints with a minimal amount of solder. He also gave us the option of using solder paste and a hot air gun (ie, the aforementioned reflow technique) or using a “mini-wave” type soldering iron tip. So even though I have successfully soldered many similar ICs in the past, I came away from the course with some new tricks. I also got the opportunity to use a “Mantis” 3D microscope for the first time, which is a great piece of gear for fine work and inspection if you can afford it. We were allowed to use it as necessary for placing components, checking placement and inspecting joints. Lead-free soldering The IPC-7711/7721 training course is not specific to any particular type of solder alloy or brand/model of tools. It is a general soldering training course and the knowledge gained by the participants can be used with virtually April 2014  23 A demonstration of reflowing BGA package chips on an XBox motherboard using an infrared heater rework system. This has a preheater under the PCB and the main heater on top, which is aimed at the area to reflow. A thermistor on the end of a stiff wire allows the user to monitor the temperature. The preheat is important since without it there would be a high likelihood of PCB damage (the board sagged visibly during reflow). This was not part of the course as such but we were all interested in seeing how it’s done so the trainer obliged. any equipment. But having said that, the Chemtools IPC training courses use lead-free products when possible and it was an eye-opening experience to say the least. While I have reworked and repaired some commercially-made boards that used lead-free solder, it wasn’t much fun because these boards typically use SAC305 lead-free solder (96.5% tin, 3% silver and 0.5% copper). It melts at a relatively high temperature (~220°C), is non-eutectic and forms dull, crystalline-looking solder joints no matter what you do. That makes solder joint inspection much more difficult and hence requires good technique to give consistent results. Before going any further, we should explain what “eutectic” means. Solder comprising 63% tin and 37% lead (63/37) is eutectic, which means that it transitions between its solid and liquid states at a single temperature, 183°C. By comparison, 60/40 solder is fully liquid (liquidus) above about 190°C and solid (solidus) below 183°C. Between these temperatures it is in a semi-solid or “plastic” state and if the joint is disturbed while between 24  Silicon Chip these temperatures during cooling, it will form a poor joint with cracks and other problems. Eutectic alloys do not have this in-between state and so are easier to work with. By comparison, SAC305 lead-free solder isn’t too bad, with a plastic range of just 217-220°C but this is still not ideal. Note that this is substantially higher than the 183°C melting point of 63/37. But it’s the dull, crystalline appearance of the solidified joints that is its worst aspect and it’s quite expensive too, due to the relatively high silver content. At the IPC training course we exclusively used a lead-free solder alloy called SN100C, which was developed by Nihon Superior Co of Japan but is also manufactured by AIM Solder. This comprises 99.3% tin, 0.7% copper plus trace amounts of nickel and germanium. It is eutectic with a melting point of 227°C. Besides the higher melting point, working with SN100C is not dissimilar to working with traditional tin-lead solders. It pays to ensure that the PCB is clean (ie, no oxide contamination) and to use a little extra flux and heat the joints for slightly longer, but it flows smoothly and otherwise behaves the way we are used to with tin/lead solders. So with good technique, it gives excellent results every time, with the shiny-looking fillets we want to see. In fact, in some tests (such as mechanical strength at low temperatures), SN100C is superior to tin/lead solder. And while we have not used this solder in a commercial environment, with reflow or wave soldering, we suspect it will be better there too, in terms of both reliability and ease of inspection. One of the bugbears of lead-free solder is “tin whiskers”. Without going into a lot of detail, tin whiskers are hair-like outgrowths which occur spontaneously and can cause short circuits while “tin pest” is where tin changes its atomic structure at low temperatures and disintegrates. Testing has shown that tin whiskers do occur with SN100C but to a much lesser extent than with SAC305 (and generally do not become long enough to cause problems). Tin pest does not occur with either alloy. To summarise, lead-free soldering is not difficult with the right solder alloy siliconchip.com.au and correct technique. There’s really no disadvantage other than the slightly higher cost of the solder itself (tin is more expensive than lead). If you want to try it for yourself, Chemtools offer specific lead-free training courses, including shorter courses (one day or half day); more details on this later. For more information on SN100C, visit www.aimsolder.com/products/ sn100c/sn100c Chemtools products As stated in the text, the IPC-7711/7721 course I took is not specific to any particular equipment, tools or products and is a general soldering skills course. However, as you may have guessed from its name, Chemtools’ primary business is manufacturing and selling chemical products, including solder, flux, cleaning solution, lubricants and so on. Many of the products supplied for the soldering course are their own formulations. That includes a syringe “AIM Australia” brand (manufactured by Chemtools) flux paste and a spray can of Kleanium Deflux-It G2 Flux Remover. I was impressed Thermaltronics As explained earlier, the training course was not about learning to use any particular equipment. However another notable experience was using the provided soldering irons which were Thermaltronics TMT-9000S stations, similar to the TMT-2000S reviewed elsewhere in this issue. For full details, see that review but I will say here that I had previously considered buying one of these irons but had dithered over deciding on a particular model. My experience using them during the course convinced me that I definitely want one, especially now that I am considering switching to lead-free solder as they are particularly suited for that task. Further experiences While not actually on the curriculum, I was curious about working with BGA (ball grid array) package ICs as I had never done it before. They are tricky because all the solder joints are under the IC package itself so they must be reflow soldered. BGAs are widely used in commercial devices because they offer the highest connection density, with some BGAs having upwards of 1000 pads. BGAs are supplied with small solder balls pre-attached to each land on the underside. When the IC is placed on the board, these balls sit on top of corresponding pads and when heated, reflow and form the solder joints. While tricky to work with, they are not out of reach of hobbyists; they can be soldered in a toaster oven, for example. Since several of us were interested in how to reflow and remove BGAs and we had finished all the required parts of the training course, we were treated to a demonstration of both, using an infrared solder reflow device. The part of the course where we siliconchip.com.au with the quality of both products. Their no-clean flux gel has a long residence time, is tacky enough to be used to temporarily hold components in place and it sticks around during soldering to provide good wetting, especially during drag soldering. It doesn’t have a particularly strong odour, either; some fluxes can produce quite acrid fumes. I especially liked the Flux Remover. I have never been satisfied with isopropyl alcohol or methylated spirits in the past because they tend to leave behind a white residue and much scrubbing and repeated applications are required; even then it’s virtually impossible to get the board completely clean. Not so with the Kleanium G2 which completely removes flux residue (even when it has burned), leaving a sparkling clean board. It’s a slow-drying formulation so it stays on the board for long enough to really attack any contaminants and leaves you with enough time to blot it (and anything it has dissolved) off before it evaporates. A clean board doesn’t just look nice, you need it to be clean to properly inspect solder joints; flux residue can easily mask faults or give the appearance of a solder bridge where there is none. It even smells nice and has a low toxicity, important for a product which you may use on a regular basis. There are in fact a whole range of Kleanium products (see photo) to suit various different situations, such as when faster drying is required in production environments or for when a more aggressive solvent is required. Like all the Chemtools products, the Kleanium range is made in Australia. Most of these products can be purchased from element14 (G2 Flux Remover part code 236636402, AIM Australia flux paste part code 182777202). The SN100C lead-free solder mentioned in the text can be purchased from RMS Parts in wire or paste form. See the following link for details: http://rmsparts. com.au/productsearch.ews?stocksearch.ewdsearchterm=sn100c SN100C solder is manufactured by either Nihon Superior Co of Japan or AIM Solder, including AIM Australia (a brand of Chemtools). April 2014  25 learned how to strip and tin wire and make connections to various kinds of terminals was also quite interesting as I had never used a turret, hook or cup terminal before and I learned better methods of stripping and tinning wire than I had been using previously. It may seem like a simple task but there are some serious pitfalls which can cause premature failure of a wire connection. It was also interesting to get a chance to apply a conformal coating to a PCB. While there is nothing especially difficult about this, I had not done so before, partly because I didn’t know what to do to remove that coating later should it be necessary to perform repairs. I got some helpful hints on what’s required for removal and on the benefits of conformal coating, such as much better corrosion resistance in applications where the PCB can be exposed to moisture and condensation. Other courses I would definitely recommend the IPC-7711/7721 course to anybody who wants to learn how to solder or improve their existing skills as it covered a wide range of topics including many important techniques. But you may not necessarily have the time to take a 3-day course or feel that the cost is justified. Chemtools also offer a number of other IPC training courses including one-day courses which readers may wish to attend. Note that many of these (including the one I attended) consist of a core curriculum and optional modules which teach additional skills and knowledge. In general, I would recommend including as many modules as possible. In addition to IPC-7711/7721, the available courses include: • Fundamentals of Soldering: 1-day course includes soldering SMD & through-hole components, cleaning, inspection, equipment maintenance and lead-free soldering. Consumables and tools provided. • Introduction to ESD (Electrostatic Discharge): a 2-hour course covering ESD and ESD mitigation techniques and tools. • Advanced SMT & Through-Hole Rework/Repair course: a 1-day course with the option of a second day for hands-on PCB repair training. Includes soldering fine-pitched 26  Silicon Chip This is the practice board I assembled as part of the training course. As you can see, it has a number of different types of components including various different kinds of surface-mount parts with varying pitches and lead types. We used a variety of different methods to solder these components and inspected the joints to ensure they were formed correctly. We also covered it with a conformal coating (which glows under UV light, so you can check that it is fully covered). This coating has a shiny appearance and protects the board and components from dirt, dust and moisture. • • • • • packages using a hand-held iron, hot-air wand or infrared equipment, through-hole component removal using vacuum desoldering tools, cleaning, equipment maintenance and lead-free soldering. Lead-free soldering: 1-day course, covering specific requirements of using lead-free solder as well as general soldering skills. Production Line Soldering: 1-day or 2 x ½ day course. Acceptability of Electronic Assemblies (IPC-A-610E): A 3-day course covering skills required to accurately recognise faults in electronic assembly (eg, poor solder joints). Requirements for Soldered Electrical and Electronic Assemblies (IPC-J-STD 001E): A course covering the processes and procedures for reliable soldering and inspection of through-hole, SMD components, wires and terminals. Requirements and Acceptance for Cable and Wire Harness Assemblies (IPC/WHMA-620B): Covers crimp termination, insulation displacement connectors, soldered terminations, moulding, potting, splicing, bundling, marking, labelling, solderless wire wrap connections and more. Attendees who complete IPC courses, show satisfactory performance and pass the test are qualified as Certified IPC Specialists. This certification is valid for two years (with the possibility of a 90-day extension to allow for re-certification). Chemtools travel around Australia, offering courses in major cities at various times. If you in or near a major Australian city and are interested in attending a course, call them at 1300 738 250 or (02) 9623 3670. Also, check their website: www.ipctraining.com.au Courses are scheduled when there are enough participants to make a class, so they may be able to offer you a place in a course that has already been scheduled or alternatively, you can wait SC until one becomes available. siliconchip.com.au