Kevin, Using LPI in an attempt to tent vias does lead to exposed copper which could be an issue in some extreme environments. The bigger concern with this process in my opinion is entrapment of any chemistries that the board is exposed to after the LPI has been applied. When LPI is applied, typically on the first side the vias will be tented (sealed off) but on the second side a percentage will either be open or have a pin hole in the tent. The ones with the pin holes can suck in liquids (fluxes, cleaners, etc.) that can not be removed by subsequent cleaning processes. These chemicals are now trapped in a copper lined cup, that at some point can corrode into an open via. While there are several alternatives that use addition processing steps and add to your costs, a single application of LPI on each side will result in the potential for chemical entrapment. On Au/Ni boards, the only difference would be the added layer of nickel over the copper. Norm Dill Harris RF Communciations [log in to unmask] _________________________________ Subject: Re[2]: Soldermask Tented Vias Author: [log in to unmask] at corp Date: 6/19/96 3:53 PM Rodger - I vote for your suggestion! If you look at an assembly with solder mask closely, one will find that the sidewalls of many surface features are bare copper. I think that the electronics industry in general has quite a bit of exposed copper functioning in the field with few problems. The exposed copper issues I have been working seems to be a "culture" issue (military product primarily) - the standard question has been "won't it corrode if the copper is exposed?. There will be design and use environment specific cases where bare copper will be a problem but overall there are gains to be realized. Using bare copper would mean that the printed wiring board would see one less thermal excursion (no HASL or Refuse operation) which can only be a good thing from a reliability standpoint. Lee Parker of AT&T gave me a paper on the corrosion of exposed copper in several environments over a 30 year period - if I can find that paper I'll post it here on TechNet. Well TechNet - anyone else in support of bare copper? Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: Soldermask Tented Vias Author: [log in to unmask] at ccmgw1 Date: 6/19/96 10:05 AM I don't know much about your soldermask issue, but I would like to see some discussion of the exposed copper issue. We have felt for a long time that any exposed copper was unacceptable but with the industry switching over to OSP more and more, we have to accept a limited amount of copper exposure (when SMT pads don't get paste). If you are making SMT-only boards which don't flow across a wave solder then the amount of exposed copper goes up tremendously. I recently talked to people at a company which is very prominent in the electronics industry and has been allowing a large amount of exposed copper on their PCB assemblies (look inside your PC and see how much exposed copper you can find). They have done a significant amount of temperature and life testing and have seen no problems due to exposed copper. If this is true, isn't it time to stop worrying about exposed copper and start making boards and assemblies cheaper? Regards, Roger Held Hitachi Computer Products (America), Inc. ______________________________ Reply Separator _________________________________ Subject: Soldermask Tented Vias Author: [log in to unmask] at Internet-HICAM-OK Date: 6/19/96 8:48 AM Good Morning, We usually require soldermask over bare copper and tented vias (less than .020"). This typically means that the soldermask is dry film. If a tented via is not required and liquid soldermask is used, it appears that the soldermask is suspect to flake off near the via knee, leaving a small amount of exposed copper. Is liquid solder mask over bare copper compliant with vias when the plating is eletroless nickel - immersion gold? Does the plating type matter? Is the suspect of exposed copper a non-issue? Thank you in advance of any comments. Kevin Thorson Lockhead Martin Eagan, Mn