======== Original Message ======== Sender: [log in to unmask] Received: from simon.ipc.org (IPC.ORG [168.113.24.64]) by arl-img-7.compuserve.com (8.6.10/5.950515) id IAA00673; Wed, 3 Apr 1996 08:14:54 -0500 Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI) id HAA29355; Wed, 3 Apr 1996 07:14:47 -0800 Resent-Date: Wed, 3 Apr 1996 07:14:47 -0800 Received: by ipc.org (Smail3.1.28.1 #2) id m0u4S0K-00006mC; Wed, 3 Apr 96 06:49 CST Resent-Sender: [log in to unmask] Old-Return-Path: <[log in to unmask]> From: "Dill, Norm J" <[log in to unmask]> To: "'IPC Technet Input'" <[log in to unmask]> Subject: FAB: Tenting Au/Ni vias with LPI? Date: Wed, 03 Apr 96 07:44:00 EST Message-ID: <[log in to unmask]> Encoding: 12 TEXT X-Mailer: Microsoft Mail V3.0 Resent-Message-ID: <"jnwkP2.0.P7F.ZFdOn"@ipc> Resent-From: [log in to unmask] X-Mailing-List: <[log in to unmask]> archive/latest/3278 X-Loop: [log in to unmask] Precedence: list Resent-Sender: [log in to unmask] Typically when LPI is used to tent vias, one side of the board will seal and the other may have pin holes or openings in the mask that covers the via. This creates a copper lined cup capable of trapping any subsequent chemistry liquids that it may be exposed to (fluxes, cleaners, etc.). Is this concern reduced when nickel/gold are plated over the entire copper board? Please share your via tenting experiences. Thanks. Norm Dill RF Communications [log in to unmask] ======== Fwd by: Tony King / N ======== I hear this concern sometimes from customers or designers, yet as a board manufacturer have never seen a failure in a printed circuit board attributed to copper attack in a hole partially filled with mask. Further indication of entrapped solutions in the hole should be detected at ionic cotamination testing, yet again has not been seen. There are several options to consider when designing product for plugging holes with mask, in reference to the solder mask artwork design, a hole should be plugged (exposed to light) from both sides of the hole or neither side (not plugged). The LPI process outcome is very unpredictable when exposing a mask filled hole from one side only at image.(dependent on the amount of mask in the holes, the degree of developing, light intensity etc.) If the design requires the holes to be plugged completely, this can be done prior to (or after) primary lpi coat using a screened dot pattern. The dot pattern plugging operation can also be performed after HAL to allow solder coating of the copper prior to plugging if corrosion is a concern. Some customers absolutely require holes to be plugged from one side while leaving the other side open for testing reasons. This dot pattern screening operation must be done after HAL to insure the partially plugged hole is adequately cleaned after soler coat. Though I have not seen copper fail, I would expect nickel/gold to present better protection against possible corrosion, though the gold would be too porous if immersion coated, electroplated gold would be better. Tony King Elexsys International Inc 603-886-0066 [log in to unmask]