Proper PCB Storage — The Top 3 Hazards

It’s late. Do you know where your printed circuit boards are? Let me rephrase that: Can unused PCBs be stored for future use?

Yes, they can – if stored properly. Keep them wrapped up, or sealed in a bag. Anti-static isn’t necessary in this case, but it won’t hurt. Keep them in a cool, dark place. Keep them clean. Do your best to avoid dropping them on the floor and stepping on them.

The board in this photo was left out on a desk for a while, and then shoved into a desk drawer. The environment took its toll on the immersion sliver finish, making it very much unusable.

PCBstorage

What can go wrong:

1. Fingerprints. The oils on your finger can etch fingerprints into ENIG or immersion silver board surfaces. If you plan on committing a crime go ahead and do this so we can catch you. If you aren’t going to start a life of crime be careful to not get your fingerprints on the board surface. Handle on the edges, or at least, don’t touch any exposed metal.

2. Moisture. Moisture is good for your skin but not for your PCBs. Over time, PCBs can absorb moisture, especially in a humid location, or the ocean. If thrown into a reflow oven they then might laminate. Store boards in a dry environment. If stored for a long time, you may want to pre-bake them prior to use.

3. Atmosphere. Sometimes dirty air can contribute to tarnish or corrosion on the exposed land pads. Dust can settle onto the boards as well. Tarnish and dust can usually be cleaned off, but corrosion can’t. Wrap up your boards for long-term storage.

Treat your boards well and you can likely use them at a later date. Don’t treat them well and you may need to replace them, wasting a bunch of money. Often, the damage isn’t as clear as in the above photo, but could still lead to poor solderability.

Duane Benson
Don’t surf on your silver

http://blog.screamingcircuits.com/

Electronics Shelf Life

Do parts and PCBs have a shelf life? Well, yes and no. I have some 7400 series logic chips in DIP form that I bought back in 1980. Every now and then, I pull one out and put it into a proto board to test some circuit idea I’ve got. They still work thirty years later. I haven’t taken any special care in storage either. Some are stuck into anti-static foam. Some are not. All are sitting in a mini-parts bin without any moisture protection. I guess they do get a little shielding from light, but basically, they’re just hanging out. They’ve been, at various times, in the attic, in the basement, in the garage or in the house.

That may seem like good evidence refuting a shelf like for parts. And today’s parts are even more robustly Bent pins in strip designed to start with. Still though, if I use any of those parts, it’s generally in a proto board or a socket. Sometimes I have to straighten the leads a bit. A lot of things don’t matter so much at low temperatures, low speeds, low volumes and large geometries.

It’s different when you have fine pitch parts being picked up and placed by a robot and then run through a 10-zone reflow oven. Oxidation that doesn’t matter for a socketed prototype can interfere with the solder adhesion. Bent pins or missing BGA balls can prevent the part from fitting. Moisture absorbed over time can make the chip act like a popcorn kernel when in the reflow oven.

That’s not to say that you can’t use old parts for a prototype these days. Just give them a good inspection before sending them off for assembly. And, if they’re moisture sensitive parts or have been stored in high-humidity areas, consider having your assembly house bake them before assembly. The same goes for raw PCBs too. Overly moist PCBs can delaminate during reflow. Some PCB finishes such as immersion sliver and OSP can tarnish or degrade over time too.

Duane Benson
Archaeologists, we are not

http://blog.screamingcircuits.com/