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Fig. 1 - Integrated Circuit Without Cover
Fig. 2 - "Purple plague" Failure
An integrated circuit can be thought of as a miniature circuit board, as shown in Fig. 1 above. Gold wires (2) running from the lead frame (1) are bonded to aluminum pads (3) on the circuitry.
The I.C. in the picture was soldered with a 700°F/371°C iron and the bond (3) was cross–sectioned. The electron microscope scan of that cross–sectioned bond is shown in Fig. 2. The gold bond (A) has reacted with the aluminum pad (D) to form an intermetallic (B). Because of its color, the intermetallic is known as "purple plague."
The intermetallic has significantly greater electrical resistance than either gold or aluminum, so thicker intermetallics mean degraded electrical properties for the component. Depending on the sensitivity of the component, the increased resistance created by a thicker intermetallic can cause system failure.
Adding to the degradation, the gold/aluminum intermetallic occupies less space than the gold and aluminum individually, so gaps ("Kirkendall voids") occur as the intermetallic thickness increases. Eventually, breaks occur at the edges of the bond as shown in Fig. 2 and the component fails.
Intermetallic growth occurs even at room temperature and all electronic components will fail eventually. But the rate of intermetallic growth at room temperature is so slow that many decades will pass before a component fails. Heating the component to soldering iron temperature for just a few seconds can cause, on the other hand, can cause failures at test or shortly after the product reaches the customer. The reason is the exponential growth of intermetallic as temperature increases.
The Arrhenius equation says the rate of chemical reactions roughly doubles with every 10°C increase in temperature. The thermal aging inflicted by a soldering iron at 350°C-400°C — that is, roughly 660°F to 750°F — can, therefore, be profound. Under pure Arrhenius conditions, The intermetallic formation at 350°C would occur at 8,589,934,592 (i.e. 8.59 BILLION) times the rate at formation at 25°C. Even if the component has an operating temperature of 50°C, the difference in the rate of intermetallic formation at soldering iron temperature would be 1,073,741,824 (i.e., slightly more than 1 BILLION) times greater than at room temperature.
The actual rate does not actually increase exponentially, however, because intermetallic formation requires contact between unreacted gold and aluminum. As the intermetallic layer increases, migration of fresh gold and aluminum through that intermetallic becomes more difficult and the rate at which additional intermetallic forms slows. But intermetallic still forms millions of times faster at soldering temperatures even taking account of the intermetallic barrier between the gold and aluminum.
The danger of overheating components during hand soldering have been well known since the earliest days of solid state components. Consequently, when solid state components first appeared, work instructions required attaching metal clamps ("heat sinks") to the lead next to the component body. The clamp absorbed the heat before it could reach the body, protecting the component. Requirements for the use of heat sinks still exist in industry standards but are ignored because modern components are so tiny that attaching a clamp is impossible.
If heat sinks can't be used, what can be done to prevent heat damage? Every soldering course except Science of Soldering© falls back on two faulty procedures: solder "quickly" and use a low temperature iron.
Telling operators to "solder quickly" raises the question "how quick is quick"? Typically, the trainers define "quickly" as 3 seconds or less. But catastrophic damage can be inflicted on an I.C. in much less than 3 seconds. (On the other hand, 3 seconds may not be adequate when working with larger components or thick circuit boards.) There is nothing reliable about soldering "quickly."
The instruction to set the iron at a low temperature also makes no sense. The iron must be set to the temperature required to solder the components with the highest thermal mass. So a temperature below 315°C (600°F) is generally not practical. In the best case, one second exposure to the lower temperature iron will "only" age a component 536,870,912 times as quickly as aging at room temperature.
Whether soldering "quickly" or at "low" temperature, the damage to components can be disastrous. Components subjected to such soldering conditions may not fail at test but will not last as long as the customer expects..
Of course, there is enormous variation in the temperature profile from one manually soldered connection to another. So not every component soldered by hand will fail at test. Some may live long, productive lives. But many will not. The question, then, is how many failures are "acceptable?"
Components can be soldered with 370°C (700°F) or hotter irons without seriously damaging the components. But it can't be done using the methods which are taught in other soldering training.
We devised a simple yet scientific and absolutely reliable way to solder components using that 370°C/700°F or hotter soldering iron without subjecting the component to temperature above 260°C/500°F. In other words, our hand soldering technique prevents components reaching temperatures greater than those they would encounter in machine soldering. There is no special equipment required; it works just as well with a $100 soldering iron as with a $1,000 iron. And it is just as fast as using the traditional techniques found in all other solder training. You will be astonished by the simplicity and effectiveness of our heat control technique.
The U.S. Navy commissioned laboratory analysis that verified the effectiveness of our method for prevention of heat damage. If you would like a copy of the report, please use this form.
Our scientific heat control technique is taught in our Science of Soldering© course — and nowhere else.
When someone had the idea of bringing in an expert of soldering we all thought the idea was crazy, but now that we had the expert in and trained our employees we know that it was a great idea! We have had some failures in the past that we now know were related to improper solder joints. The class uncovers multiple variables that are critical in creating a proper intermetallic bond between the two materials you are trying to solder. The training was very informative to our production team as well as some of our quality and engineering personnel. I highly recommend Science of Soldering©.
Ritz Instrument Transformers, Inc.
Lavonia, Georgia 30553
The theoretical education in day one followed by a full day of both "good" and "bad" hands-on in day two is near priceless.
Anthony "Tony" Nichols
Motivo Engineering LLC
Gardena CA 90248
There is a difference between thinking you know how to solder and knowing how to solder. Jim Smith from Electronics Manufacturing Sciences took the time to train our production staff and our engineering team in proper soldering techniques. We are applying his training techniques to our policies and procedures and quickly took his advice in obtaining the proper flux, solder and other recommended equipment. His training was professional, quick, thorough and easily followed, even for us engineers. We would strongly recommend Jim and EMS to any company that is need of good sound soldering training that is based off of true scientific principals.
Senior Process Engineer
Spokane Valley, WA
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The Science of Solder training was very valuable for both hand and machine soldering techniques and was applicable to process controls as well. Especially rewarding, was how Jim Smith explains the “why” behind the techniques, so engineers and technicians understand the logic behind the assembly processes they are implementing and executing on the production line.
The training class was incredibly beneficial to the entire RF Code Team and I would recommend it to anyone.
Director of Manufacturing & Operations
RF Code, Inc.
When we chose EMS for our company wide training, we did so based on some publications we read by Jim Smith and the purpose-driven solder training that focuses on comprehending soldering. It seemed that our management team’s observations and desires to reduce wastes and create efficiencies were in line with the training that EMS provides. We are happy to say we were correct.
The presentation and relevance to our needs were spot on for our company. Jim was utterly professional in giving the best service possible before, during and after.
The Science of Soldering© “recipe” for correct, science based application is simple and the methods of teaching were enjoyable and welcomed by our staff. At Commutron Industries Ltd. it is our desire to provide our customers with the best product and service possible. We believe this training and the resources provided have properly supported this.
Commutron Industries Ltd.
Elbow, Saskatchewan Canada S0H 1J0