MR MARK A WARYCKA wrote:
> 
> Good Day,
> 
>          This is a request for some assistance on a wavesoldering
> problem that we are currently experiencing on some mixed technology
> boards that we process. The boards have surface mount top and bottom
> and when the process is set to wave the bottom side with no defects
> we are experiencing a problem with some top side surface mount IC's
> de-soldering! I have tried using soldering pallets set at
> approximately  a 30 degree angle with some success but it slows down
> the processing time and the top side components still come loose.
> Initial profiling indicates that the top side of the board is showing
> temperatures below the eutectic point of the solder paste being used.
> When the boards are processed without the pallets the defect rate
> increases dramatically but the incidence of topside component des-
> soldering decreases! The wavesolder machine is a T/D Nu-Era with
> dancer wave and the flux being used is Kester 2331-ZX. Topside
> preheat temperatures just prior to wave entry are around 185 degrees
> F.
> 
>       Another question is in regard to voids and blowholes occurring
> on a PTH board that is auto-inserted. Just can't seem to get rid of
> them. The boards are inspected at incoming for voids in the plated
> thru holes. Profiling indicates that all process parameters are
> correct. Any ideas?
>               From: Mark A. Warycka
>                        Process Engineering Manager
>                        Electronic Systems, Inc.
>                        Sioux Falls, SD
> 
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Mark, blowholes and voids in PTH boards are due to two main reasons:

	1. PCB laminate moisture
	2. Poor quality copper plating in barrel 
           ( rough drilling, thin copper, pin holes, plating voids etc)
Two factors when present together can affect blowholing and solder voids 
in PTH joint. Examine your as received boards for plating defects in 
barrel and try drying your PCBs before soldering.

As regards your reflow of SMT component on top surface during wave 
solder, I have a question. Are there vias in the SMT pads? Many times the 
wave will reflow the solder in the pad via and suck the sodler out of SMT 
joint on top.
-- 
Pratap Singh
Tel./Fax: 512-255-6820
e-mail: [log in to unmask]

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