Typically, the volume of solder on a component lead is not sufficient in all cases to provide a large enough solder fillet. Was your board coated with solder (hasl)? This would make a difference. there may have been enough solder (hasl) on the board to provide for solder volume (thought not typically well controlled for consistency pad to pad and across the pad). Fine pitch components are more sensitive to solder volume. Too much will cause shorting. A SnPb plated board with well controlled SnPb thickness and having all known and controlled lead solder coatings may allow the assembly supplier to obtain good solder joints without additional solder volume in the form of "paste". Most common approach is indeed to apply additional solder ( a mix of small balls/beads of solder suspended in flux) through a screen prior to component placement. In the end though, the real question is: Did your board meet the requirements of IPC-610? Do you have a component lead pull requirement and did you pass it? Did you have access opens at functional test? Were the products reliable in testing? Changes in component suppliers may affect your assembly supplier's set-up (with variations in component lead solder levels). Jim Herard KBL, Product Quality Engineering IBM Microelectronics Endicott t/l 857-7026 ---------------------- Forwarded by Jim Herard/Endicott/IBM on 08-12-97 08:01 PM --------------------------- [log in to unmask] 08-12-97 06:18 PM Please respond to [log in to unmask] @ internet To: [log in to unmask] @ internet cc: Subject: [TECHNET] ASSEM: flux alone or flux with solder Hi Technet My company recently had a PWB assembled. It had about 75 SMT IC's some with 0.5mm lead pitch. The assembly house said they silk screened on flux only and allowed what solder was on the PWB pads and the leads themselves to effect the connection. Is this usual?? I thought that a slurry of flux and granulated solder particles was applied to the board prior to placement and heating. They used a hot air heating system and we had many cold solder joints especially in the PLCC sockets. In about two weeks we're having more boards assembled. I welcome advise on how/what to specify to the assembly house. Thanks in advance - Ray Klein [log in to unmask]