As a PCB user we specify LPI, then HASL, followed by a secondary "plugging" operation from the second/bottom/solder side of the PCB using a screen printable solder mask. The plug aperture is large enough to adhere to the LPI around the via perimeter. This does add cost since it is an additional process, but it avoids the issues of entrapped flux. We specify this process whenever we have components on the second/bottom/solder side of the PCB and whenever via to via spacings need to be reduced. It makes the wave soldering process much more forgiving and permits vacuum pull down for testing on double-reflow assemblies. Dick Krug, Racal-Datacom, Sunrise, Florida [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FAB: soldermask plugged vias Author: [log in to unmask] at ftl03 Date: 7/23/96 1:15 PM Just curious: We often have customers requesting that the (LPI) soldermask be screened/floodcoated to plug vias with soldermask. I understand the reasons behind the design; however, I'm concerned about potential contaminates being trapped in the via, especially from the HAL or assembly process. This soldermask process can produce vias that are partially to fully plugged from one (or both) sides of the PCB. This can cause inadequate rinsing and cleaning of the vias during the HAL or assembly process. Any other ideas or concerns? Has anyone looked at this issue in detail? (This soldermask process can also produce exposed copper in the via, which has been discussed on this forum. I believe the OSP surface finish would be a much safer choice with this via/soldermask design). Thanks, Dave Boggs Merix Corporation E-mail: [log in to unmask] *************************************************************************** * 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. * *************************************************************************** *************************************************************************** * 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. * ***************************************************************************