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64 DESIGN007 MAGAZINE I SEPTEMBER 2020 The Life of a PCB If there's one thing in life that really feels the pressure of being in the hot seat, it's the PCBs that we design. After putting up with the trauma of having copper added and then etched away through exposure to ultraviolet light and various chemical baths, you would think that the PCB would deserve a little break. Instead, the board goes from the frying pan into the fire, so to speak, as the different layers get laminated together. This involves a great deal of heat and pressure, as the epoxy in the prepreg is melted to fuse the PCB lay- ers together. Next comes drilling and plating, which is also no picnic, and by this point, the heat and pressure should finally be over for this little guy, right? But now the board needs to be assembled. Our plucky hero has gone through all kinds of processes to complete its fabrication, includ- ing some intense scrutiny by both automated equipment and human inspection. Now, it's back into the oven again—literally—for PCB assembly. Once the board has had its compo- nents pasted down onto it, it will be subjected to temperatures in the solder reflow oven that can get up to 255°C. That is almost 500°F for those of you who are thinking that perhaps it really isn't so bad. Let me just say this; there isn't a sunblock in the world with an SPF-value high enough to help with this kind of heat. Not every PCB that is manufactured will go through the solder reflow oven—you're right. But if they don't go through reflow, they're most likely go through wave solder instead. If you're thinking that going through a wave sounds a little more pleasant than going through an oven, think again. We're talking about a molten wave of solder, which can get up to 270°C if lead-free solders are used. How would you like to dip your toes into that kind of a wave? Thermal Management for PCB Designers: Staying Out of the Fire Tim's Takeaways Feature Column by Tim Haag, FIRST PAGE SAGE

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