Declan Moriarty wrote:
> On Fri, Nov 14, 2003 at 09:54:18PM -0800, Fred Townsend enlightened us > thusly > > This is a very old problem. You have what is known in the trade as wet > > boards. In other words, there is moisture trapped in the PCB > > laminate. This is typical of poorly manufactured boards. Do you have > > plated through holes? If so the plating quality is suspect too. > > > > The simple solution is to bake your boards before soldering. Use an > > oven set somewhere between 105 to 120C for 4 hours. Any hotter and you > > will damage the resin coat. > > Thank you all for the helpful advice. I obviously mislead people AGAIN, > as it was a Sharp TV (Brazilian?) and I didn't manufacture it. I did > mention something about sticking my head into a TV with a beam limiting > fault; This got snipped early on and people convinvced themselves I was > manufacturing Brazilian Monitors. > > The advice on heating the circuit board was about five years too late > for Sharp, but very welcome, since it answered the questions that raised > themselves in my mind. The board was not plated through, FWIW. > Interestingly, if plating through was intact and I really heated the > joints like that, I'd destroy the via, wouldn't I? I read somewhere > about water expanding to 1600 times it's own volume as it turns to > steam. It would be fun to watch - with goggles on! > The plated through hole (PTH) process is a wet process. Hole quality is very important in order to minimize wicking of moisture in the PTH process. Even in the best of processes a small amount of moisture is trapped after plating. If the laminate is FR4, the moisture is forever encapsulated unless there is a fissure or void in which case the moisture vents during the solder process. This is why a solderability test is considered a good measure of PTH quality. If a paper or phenolic laminate is used the moisture from the PTH process will defuse through the laminate. This will cause long term corrosion and galvanic noise problems, particularly in climates like rain forests and London Fog. This is why these laminates are seldom used for PTH. If the board does not have PTH the requirement for high quality holes is diminished. Some manufactures take at vantage of this to use their drills at the wrong speed and beyond their normal lifetime. These "cheaper" boards are often more expensive to assemble. This is one of the reasons PTH boards in the US are the standard, even for single sided boards. Fred Townsend > > The fact that I haven't met that in Ireland (a damp country) testifies > to the quality of Irish pcbs, doesn't it? > -- > > With best Regards, > > Declan Moriarty. > -- > Author: Declan Moriarty > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). -- Author: Fred Townsend INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
