Replacement LED?

How were the new caps stored? If it is where they can adsorb moisture, you can damage them with an iron that is too hot.

Not at all. That was very interesting. Thanks Jeff and everyone.

Well, I must admit that I didn't take any special precautions. Methinks that the relative humidity in my office runs between 40% and

60% but is not monitored or recorded. Occasionally, it gets low enough to where static electricity becomes a problem, or high enough to where I'm rather uncomfortable, but those are rare. The caps a mix of cut tape and loose bags stored in Ziploc bags (mostly pink anti-static) and in paper coin envelopes. Nothing in hard plastic or metal drawers that might chip or crack them. Although I know that these caps make tolerable hydrometers (and microphones), I don't think they can absorb enough moisture from the air to where a steam explosion would be a problem.

I did some digging to see if humidity might be a problem in storage conditions. There were plenty of notes on how a cracked capacitor might allow water to enter the dielectric. Soft (solder) termination is the recommended fix. Some suggests pre-heating the capacitors before soldering to drive off any moisture. One demands that the caps be used within 12 months. I didn't see humidity as being a problem until AFTER the capacitors had cracked. It would take some time for the moisture to alter the capacitor characteristics. With my hand soldering technique, I managed to instantly produce shorted capacitors, which methinks was more likely due to uneven thermal expansion, than to moisture incursion.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I haven't had any problems with cracking but I used to have problems with end caps falling off. I haven't seen the issue for some time, though perhaps it was a problem with the manufacturer. Our purchasing group prefers Murata, so that's what I use (GRM series).

For the normal cold tweezers, I agree. For the hot ones, I think it's mainl y the surface tension of the molten solder that's the issue.

When debugging boards, it's often useful to be able to pull off some part t o measure it or see what the circuit does without it. It's way quicker to p ut the original part back than find a new one and replace it. I agree that you don't want to do that when reworking a production board.

Cheers

Phil Hobbs

We pre baked some boards and other components before assembly and reflow. That eliminated cracked multilayer SMD capacitors, tombstoning of two lead components and losing end caps. That was in N Central Florida which has plenty of humidity problems. The so called HVAC 'engineers' were clueless about how to control the humidity, so we had to resort to baking. LSI SMD ICs were backed and heat sealed into antistatic bags with moisture adsorbing packets.

Sure, baking humidity sensitive parts is common before pick-n-place. It's a bit less common when hand (de)soldering, though. ;-)

We had a high failure rate on hand soldered FIR chips, before we started baking them. The bottom of the packaging was the thinnest, and it would bow out as it released steam during hand soldering. No one in EE or ME believed me, until I finally got them to try it for themselves.

Grin, one of Mueller's theorems is; If it happens it must be possible.

George H.

Sure. If a component can absorb water in its packaging, there's no reason to assume that it won't after it's placed.

AKA: Murphy was an optimist. He was sure things would go wrong! :)

Are you still using small NTSC color monitors? I just bought a couple of these to use with security cameras. They are supposed to be about

4.3" screens. They run on 12 VDC and cost under $18, each.