Hi Paul, Years ago, the military high reliability soldering standards required PTHs to be filled with a solder plug (wave soldered only, 25% recession acceptable) or wire (swaged stud or clinched "C" or "Z" form) soldered in the holes of type of 2 and 3 printed wiring boards. After extensive testing and evaluation (data was also presented to the military folks by industry), it was determined that the via holes could be left unsoldered without compromising reliability of the interconnection. The one drawback is partial fill of these via holes, when subjected to stress and strain, the forces imparted on the PTH structure are not equally distributed. As such, this can cause the PTH to fail prematurely. As such, it is better to either fully fill the hole or leave the hold unfilled. With respect to tenting of vias, I look at the following factors: gasketing during in-circuit testing minimize the amount of exposed conductive circuitry - shorting potential - cleaning challenges In light of the above, it all depends on your end item application and environment. If you're worried about the reliability of your holes with respect to wall thickness, I would specify what you want to your supplier and then verify. As Moonman says, "specify, verify and never trust". The only time that I would leave PTHs uncovered would be for test purposes, but I would normally specify pads/targets for test points. Steve Sauer Mfg Engineer Northrop Grumman, Xetron -----Original Message----- I am interested in hearing others views in regard to allowing the wave soldering process to fill the vias with solder or tenting the vias with soldermask and how this relates to reliability. I am seeing more and more designs with the vias covered. Wouldn't allowing the vias to fill with solder increase the reliability of the PCA? Or is this a matter of covering for the "sins" of the bare board manufacturer's plating process? Expecting .001" but getting .0007-.0008" copper plating. Should via's be left uncovered? --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------