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From: "Tom Rapp" <[log in to unmask]>
Organization: Comptronix Corporation; Guntersville, AL
To: [log in to unmask]
Date: Tue, 10 Dec 1996 10:03:25 -0600
Subject: (ASSEM) Wave soldering SOT-23
Priority: urgent
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Good Morning Tom,

I have seen many successfull sot wave soldering operations using 
assorted fluxes (water soluble and rosin) and pad geometries, however, 
nearly all cases were utilizing "dual wave" soldering machines.

The pricipal here is to solder the pcb first with a turbulent wave 
biased towards the exit end of the machine, producing less than optimum 
results (bridges) yet overcoming the "shadowing" effect of the 
component. This is followed by the more conventional asymetrical wave 
with high forward velocity, and flat exit portion, matching the 
velocity of the wave to pcb. 

Corrective action might be to retrofit a dual wave to your existing 
system (we do that sort of thing, by the way) or upgrading to a new 
machine.

Another culprit could be the volatile carriers of your flux are not 
being evaporated during the preheat process. This would be very evident 
by excessive sizzling and popping as the pcb hits the wave.

Corrective action might be to evaluate proper topside temp (200-225 F) 
just prior to entering the wave. If you are using a water based flux, 
you might want to evaluate alchohol based formulas which are much 
easier to drive off the volatiles.

Regards,

Ed Popielarski
QTA Machine
[log in to unmask]
(714) 364-6614
 

We are having problems wave soldering SOT's located on the bottom 
side of the boards. The SOT's have insufficient or no solder after 
waving. I have several questions reagarding this problem.
1. Is there a recommended wave profile?
2. Is there a recommended pad geometry for SOT's?
3. Is there a recommened flux?
4. Does anyone have any reports or technical articles on this issue?
Thank You,
Tom Rapp
QE
[log in to unmask]
205-582-1800 Ext 1240

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