Estimated reading time: 4 minutes

Proper PCB Storage: Top Three Hazards

The first electronics devices I worked on didn’t have printed circuit boards. These were old, tube-based radios that I bought at garage sales or found in my dad’s junk drawers down in the basement. Individual resistors, capacitors, wires, and other components were soldered on to lugs that were connected, protected by insulating washers, to a steel or aluminum chassis.

That worked well back then, but, obviously, it won’t work with the current swarm of tiny surface-mount devices—although, some people get a lot done with the “dead bug” technique for hobby and prototype work. With dead-bugging, the IC chips and other parts are glued upside down to some surface and point-to-point wired together with small gauge wire; it’s similar to the old radio technique, but with fewer Fahnestock clips. Today, most commercial electronics are PCB-based. There may be a few devices out there that are point-to-point wired, but I can’t think of any. In many cases, wires between PCBs are even going away and being replaced by flexible PCBs.

Overall, our modern world could not exist without PCBs; they are everywhere, but they aren’t items to be taken for granted. Like most technology, PCBs need proper handling and storage. PCBs don’t last forever and are even more vulnerable before the parts are soldered on. The solderable metal surface is very thin and subject to a number of potential problems, especially if not stored properly. Once the parts are on, the solder covers the thin metal layer, protecting and strengthening it. If even more protection is needed due to hostile environmental conditions, your manufacturer can apply a conformal coat to protect the exposed metal and parts.

Before use, though, it’s all about proper handling and storage. Boards are best used right away, but they can be used later if handled and stored properly. Keep them wrapped up or sealed in a bag in a cool, dark place. Anti-static isn't necessary in this case, but it won't hurt. Do your best to keep them clean, and avoid dropping them on the floor and stepping on them. For example, the board in Figure 1 was out on a desk for a while and then shoved on to a shelf. It is as close to a worst-case example of what can happen when a PCB isn’t cared for properly. The environment took its toll on the immersion silver finish, making it very much unusable.

Figure 1: Old BeagleBoard close-up.

Top Three Hazards

Many problems we run into here at Screaming Circuits are much more subtle. Here’s a list of what can go wrong when boards aren’t treated well:

1. Fingerprints

The oils on your finger can etch your fingerprints into electroless nickel immersion gold (ENIG) or immersion silver PCB surfaces. If you plan on committing a crime, go ahead and do this so that we can catch you. If you aren't going to start a life of crime, be careful not to get your fingerprints on the board surface. Handle on the edges, or at least, don't touch any exposed metal, this is less of an issue with hot air surface leveled (HASL) boards than with immersion silver or ENIG, but it can still cause some solderability problems.

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, then might delaminate, especially at lead-free temperatures. Do your best to store boards in a dry environment. Some boards come from the fabrication shop in packaging that will keep moisture out, but some don’t. It’s difficult to predict if this will be a problem for you because it’s heavily dependent on your environment. If stored for a long time, you may want to pre-bake or have your assembly house do so before use.

3. Atmosphere

Sometimes, dirty air can contribute to tarnishing 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. Ideally, seal them in moisture resistant packaging with a moisture absorbing packet.

Treat Your Boards Well

If you treat your boards well, you can likely use them at a later date, but if you don’t, you may need to replace them, wasting a bunch of money. Often, the damage isn't as clear as in Figure 1, but could still lead to poor solderability. The finer the trace and space and component pin pitch, the bigger a concern proper storage and handling becomes. You can get away with a lot of sloppy behavior with big through-hole parts that would simply not work for a board holding small BGAs or QFNs.

To combat damage, use your boards right away, or:

1. Keep the boards in the original packaging or seal them in moisture-resistant packaging
2. Store boards in a cool, dark place
3. Handle PCBs by the edges
4. If PCBs have been out of the package for a while, ask your assembly house about pre-baking them

Conclusion

PCBs don’t always get the respect they deserve, but they are the foundation of our electronics devices. Don’t take PCBs for granted; follow these recommendations, and you should have good results with your PCBs.