Karla,

I have the same problem before.  My Pcb dimension is 16 X 18 inches.  On the
bottom side,  it contains 2241 SOT23 in combination with 1000 other 1206
components.  The solution is Double reflow and Selective wave process.  I
have been implemented this process for approximately a year already.
 Previous yield for this assy was 0 - 10 %  and currently the yield is
85%(excluding other defects it is about 95%).  Here is the process:

  1.  Bottom side paste print.  If the board requires ICT, then you need to
plug all
       open vias.
  2.  Epoxy and paste only those components that will exposed to wave.  If
you can
       redesign your PCB layout, then you should allow enough clearance so no

       component  is exposed to wave solder.
  3.   Placement
  4.   Reflow the bottom side, not curing.
  5.   Paste print top side.  Be careful when using support pin
  6.   Placement
  7.   Reflow top side.  Make sure the PCB is sitting in the support frame.
 Do not let
        the board rests on the mesh conveyor.  Don't worry about the heat on
the
        bottom side of the board.

Up to this moment, I have all my assemblies change to this process.  I'll
hope this help.  Let me know the result.

Tuan

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