On 10 December, Tom asked, and Ed answered:
     
     
>> 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
     
     
     Tom,
     
        What Ed said is good, although I might tend to go just a "smidgen" 
     higher in my board temperature prior to wave...something more like 230-250 
     degrees F....(works out to between 110-120 degrees C.). Another thing, it 
     helps a lot if the components are oriented correctly to the wave. Gimme' a 
     second here ta' boot-up my "Asciicad"...
     
     Like this:
     
                             PCB                       Wave
                  _________________________            %%%%
                 |                         |           %%%%
                 |        ___||___         |           %%%%
                 |       | SOT23  |        |           %%%%
                 |       |________|        |           %%%%
                 |        ||    ||         |           %%%%
                 |_________________________|           %%%%
                                                       %%%%
                   Direction of Travel------>
     
     
     
     
     
     Now for the pad geometry, and it's right outta' the IPC 782 manual in 
     subsection 8.6...is below:
     
      
           ______________________  _________
          /|\    /|\              |         |
           |      |               |         |
           |      Y               |    +----|-------------
           |      |               |         |           /|\
           |     \|/_____________ |_________|            |
           |     /|\                                     |
           |      |                                      |
           Z      G                    +                 C
           |      |                    |                 |
           |     \|/____ _________     |     _________   |
           |     /|\    |         |    |    |         |  |
           |      |     |         |    |    |         | \|/
           |      Y     |    +    |    |    |    +----|---
           |      |     |         |    |    |    |    |
          \|/____\|/____|_________|    |    |____|____|
                        |         |    |         |
                        |<---X--->|    |<---E--->|
     
     
         "Z"(mm)         "G"(mm)         "X"(mm)        "Y"(mm)  "C"(mm) "E"(mm)
      MIN.     MAX.   MIN.     MAX.   MIN.     MAX.       REF.     REF.    REF.
      3.40    3.60*   .80      1.00   .80      1.00       1.40     2.20    .95
     
     *NOTE: If a more robust pattern is desired for wave soldering, add .2mm to 
     the "Z" dimension.
     
     
     
     
     As for flux, what I've used is either Kester's 2331-ZX Organic Water 
     Soluble, or Alpha Metals WS370F...they both work good, although you have to 
     add thinner a little more with the Alpha to keep the specific gravity where 
     ya' want it...
     
     
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