John, Continuing the saga of meniscus in the PTH: Entrapment of flux and other process chemicals but I would anticipate it to be rather remote. The major process variable would be the effectiveness of the cleaning process itself. Entrapment was, and still is a problem with tenting of larger(>20 mils) PTHs with solder mask, since most mask materials cracked during reflow and at least partially sealed prior to cleaning. I do not see the equivalent possibility here since the meniscus doesn't form a seal to the PTH. Again, there are many process variables that should be considered before making a "never happen" statement. TCE of entrapped process chemicals should not present a problem either since they are not constrained or rigid. In any case we have major variables to deal with that are case by case and process peculiar, but I have no experience with product failure due to degradation of the PWB PTHs for process chemical entrapment related to meniscus intrusion. As we discussed previously, the two schools of thought were so called "Hi Rel" which regulated against the anomaly and commercial (not necessarily Lo Rel) which really didn't see a problem. The difference being, for the most part that the Hi Rel parts had to survive environments which were commonly hazardous to the performance of the product. In those cases it was easier to address the potential through process prevention requirements than to deal with product failure that threatened National Security or loss of life. Best regards Mel Parrish MTTC Inc. At 12:57 PM 11/14/96 +0000, you wrote: snip >Yes, I can certainly see that the meniscus would prohibit wetting. And especially, in the worst of all situations - meniscus in the solder joint when in a single sided board application - the premature failure over time and temperature extremes seems quite likely. What I'm also concerned about, though, - and this is the predominate debate point, here - involves potentially compromised PTH's, when the meniscus in the holes is allowed. Won't the partial blockage of the hole create a potential entrapment of flux gases or residues? And, if that is so, it seems like at least two problems may result: 1 ) a diminished area of wetting inside the PTH (and therefore a weaker mechanical junction of less current carrying capability) and 2) the potential for a breakdown of that hole plating due to either corrosion or expansion and contraction of the trapped materials (or would it be due to the relative differences in TCEs of the plated hole and the trapped materials?). A third possiblity might include the breakdown due to increased heat generated at these highly resistive pockets. > >snip We can be reached at: e-mail: [log in to unmask] Manufacturing Technology Training Center (MTTC), Inc 543 Graaf Street Phone 619 446-5571 Ridgecrest CA 93555 Fax 619 446-4337 Web Page: http://www1.ridgecrest.ca.us/~mttc/mttc.htm Bulletin Board: 619 446-4087 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************