Ioan, If the pads are solderable after wave soldering then you probably don't have a "solderability" problem. If you were seeing partial wetting or de-wetting on the pads you might have a "solderability" problem. If you are experiencing non-wetting" on random pads then you probably have a "soldering" problem. If you see random or isolated pads that don't take solder during wave soldering but do take solder after wave soldering then I'd suggest that the pad isn't touched by molten solder during the wave soldering process. If it was it should have wet. Examine the pads that don't wet and pay particular attention to their geometry and dimensions. Also check the solder mask thickness and size of the solder mask well surrounding the non-wet features. Our experience is that random non-soldered pads are usually caused by what we refer to as the "solder mask well effect". We have a thick in-house solder mask for high voltage circuit packs and found that when the solder mask was 3 to 4 mils thick we always got many random non-soldered pads. When we control the solder mask thickness to 1.5 to 2.5 mils thick we eliminate not all but the majority of the non-soldered pads. When we use a typical LPI solder mask with a thickness of 0.8 to 1.2 mils we see random non-soldered pads very infrequently, that is if our wave soldering processes are in-control. We never see non-soldered pads on the bottom side if the features are vias. If they are test pads or component sites that don't contain a via we find that the flux we apply ( and we do use X-33-04 in one factory) collects in the well between the solder mask and the pad. When it is heated and volatilizes a bubble covers the pad and blocks solder from touching the pad. When this happens solder doesn't wet the pad. Vibrating the board or the wave during wave soldering helps "push around" these bubbles allowing solder to touch the pad. Try using a chip wave along with a laminar wave or if you already have a chip wave try increasing its pressure or oscillation. Regards, George George M. Wenger DMTS Bell Laboratories Princeton, Supply Cain Network Engineering Research Center FMA / AQA / RCA Lab (609) 639-2769 (Office); 3210 (Lab); 2346 (Fax) [log in to unmask] -----Original Message----- From: Tempea, Ioan [mailto:[log in to unmask]] Sent: Wednesday, April 04, 2001 1:43 PM To: [log in to unmask] Subject: [TN] Random absence of soder joints Hi, some time ago, Mike Bailey brought up a situation of random non-wetting on the secondary side. Well, I run into a somewhat similar problem right now. After wave soldering, I see SMT passives that are on the solder side exhibiting either non-wetting at all, or one side soldered while the other one looks just like before the wave, no sign of wetting. Even on the pads without components, the situation is the same, some pads have absolutely no trace of solder, while the adjacent ones collect solder without any problem. Not related to shading, since bad spots are even far from any component. Not related to glue contamination either, since I have trouble even with pads without components. To make it even more complicated, there is no problem to hand solder the non-wetted pads, after the wave. I refreshed the flux, ran the assemblies on two totally different machines (different preheating, fluxing), with the same poor result The process is: glue & insertion + reflow at 120C for the bottom side, only passives populated paste & insertion, reflow for the top wave with no-clean X33 flux from Multicore and regular eutectic solder board is HASL I know this is a mild flux, but it does a great job for us on much more demanding assemblies. I will try a stronger one, but cleanliness is a big issue. Now, I would like to know if Mike found something and if he could fix anything. Besides that, any hint that Technet could give would be largely appreciated. Thank you, Ioan ---------------------------------------------------------------------------- ----- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------