Now that more of us are taking advantage of the cut strips in the parts bin that we just knew “we might use someday”, it’s a good good idea to put out a reminder to look for bent pins, missing BGA balls and oxidized connections before considering them useable.
I still have quite a few old 7400 series logic chips in dual inline pin (DIP) form that I bought a few decades ago. Every now and then, I dig one out to check out some circuit idea I’ve got. They still seem to work all these years years later, despite my not taking any special care in storage. Some are stuck into decaying anti-static foam or have bad oxidation on the pins. All are sitting in boxes or mini-parts drawer sets without any moisture protection. I guess they do get a little shielding from light, but basically, they’re just sitting there. They’ve been stored, at various times, in an attic, basement, the garage or the house.
That may seem like good evidence refuting a shelf like for parts. And today’s parts are even more robust to start with. But don’t take the risks for granted. When the component’s assembly will be by pick and place robot and a multi stage reflow oven, oxidation, moisture and bent pins can be the difference between a good or a bad solder joint. Oxidation can prevent a good electrical or mechanical solder connection. Missing BGA balls or bent pins can prevent the part from fitting. Moisture absorbed over time can make the chip pop open like a kernel of popcorn in the reflow oven.
If you want to use old spare parts for a prototype, be sure to inspect them before packing them into your assembly kit. And, if they’re moisture sensitive parts or have been stored in high-humidity areas, ask your manufacturer to bake them before assembly. The same goes for blank PCBs. Overly moist PCBs can delaminate during reflow. Some PCB finishes such as immersion sliver and OSP may tarnish or degrade over time too. Static sensitive parts that have not been stored in proper antistatic packaging may not be suitable for use – unless you have a way to reliably test.
Once you have your parts, old and new (or are going to have us purchase them for you), head over to Screaming Circuits and get a quote.
Duane Benson
Three bent pins
Three bent pins
I think there’s a rhyme in there somewhere. Maybe