3/18/2024 0 Comments BiSn solder reflow profilethe profiling process remains primarily as an art. LEDs can be expensive, so special attention must be given to them. Too much heat can cause changes in the LED’s luminosity, thereby changing the final product. Some suggestions for reducing voiding in LED assembly is increased temperatures, which can be harmful to LEDs. Exactly what to change is based on the PCB density and components, finding a balance to fix one area without impacting others. These are the key areas of the thermal profile that can be changed to reduce voiding.Įven when focusing on the thermal profile there are yet more challenges. With respect to PCB reflow we should focus on Peak Temperature, TAL (Time Above Liquidus), Ramp Rate and Soak Time. Even if you’re going to experiment, you can see the results and make decisions quickly, so more uptime, and greater cost savings.Ībove is a chart of factors that impact voiding. Having gone through all the above potential solutions what’s left? In short, the thermal profile! And the best news about this is that it’s an immediate fix. Typically, we see factories invest in one of these ovens for specific products with void-susceptible assemblies. This is an expensive solution and may be hard to justify. Placement is also a key element in the voiding problem and an important place to look for problems.Īnother solution may be a new type of reflow oven, specifically a vacuum reflow or ultrasonic reflow oven. Trial and error seldom feel like a good solution. However, trying multiple stencils is costly and time consuming too. I have seen some incredibly creative stencil apertures to adjust the amount and spacing and amount of the paste deposition. Thus, changing materials may not be ideal, or even a possible, solution. Many companies don’t want to have multiple solder pastes and often a low-voiding paste is not the correct solution for all assemblies. Add to that, while this material may solve the voiding issue for some components, it may cause problems elsewhere on the circuit board. Often a contract manufacturer is given specific materials to use when assembling a board, so they can’t just change the paste without a new qualification process, which let’s face it, is costly and time consuming. However, making a change to a new solder paste is not a ‘drop in’ solution nor is it always the correct solution. One of the biggest advancements has been changes to solder paste chemistry. Potential Solutions to Reduce PCB Voiding Voiding is attributed to the flux outgassing within the solder joints when the solder is at a molten state. That is why voiding is such an important issue. We deal with the problem of voiding during manufacturing yet it’s the final effect on a product that is the key, sometimes that gets lost. Enclosed voids can cause for displacement of electrical and thermal paths as well as local concentration of power and heat.” Markus Walter, Seho ‘Whether for power electronics, electronic aviation systems, medical equipment or electronic systems for the automotive industry, solder joint voids represent a significant problem. Typically, the process window is focused around the solder paste, but often some components cannot accept the temperature tolerances of many lead-free solders. The next challenge is the reflow process window. Added to that, the mixture of circuit board components from those which cannot be seen with the naked eye to tantalum capacitors, BGAs, QFNs, plastic connectors, shields and much more. They vary from small PCB assemblies with miniaturization of parts and often a BGA to very large, heavy double-sided PCB assemblies with ground planes, heat sinks, and densely populated. Some assemblies seem to ignore any DfM (Design for Manufacturability) rules. In addition, the change in PCB (printed circuit board) assemblies is incredible. With miniaturization and many BTCs we continue to struggle to find the true causes and the ideal solutions. It continues to be a problem for lead-free assemblies, but the problem has become even more complex. Voiding has been a challenge for quite some time, primarily with BGAs, ever since the shift to lead-free soldering was discussed in the United States. Additionally, we will explore the tools that you may already have, those that are available to you right now, and how to improve your knowledge base regarding thermal profiling issues. We will look at the challenges and some solutions, primarily solutions that focus on thermal profiling. This includes what voiding is, the causes and its effect on components. In this whitepaper we discuss several aspects of the challenges of PCB voiding with bottom terminated components (BTCs). Potential Solutions to Reduce PCB Voiding.
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