Dear Jerry,
As a reflow manufacturer of course I want to brag but I also do not blame
you for your hesitation. The weight of most BGA's outwieghts the surface
tension of the solder paste. However, as Mr. Klasek pointed out, reflow CAN
be avoided on the bottom side of the board. I am sure that you have heard
before that once solder has been reflowed once the melting point of that
solder increases to a higher temperature. This is where I have to differ
with Mr. Klasek, we have not found chillers to be necessary. After reflowing
the BGA's on the top side and inverting the board, we run the assembly
through an ETS CUREFLOW that has both top and bottom convection heating. We
use a profile that uses standard temperatures on all 6 top zones (165C,
175C, 160C, 160C, 185C, 245C) and then set all bottom zones to ambient
temperature (or room temperature). This creates differential heating on the
assembly by heating the top side of the board and cooling the bottom side
of the assembly. This creates a big enough temperature delta to keep the
bottom side components from reflowing a second time.
Of course this method requires two passes through the reflow oven whereas if
all the BGA's where on the top of the board you might be able to solder both
sides with a single pass through reflow.
If you would like to discuss this further I can be contacted at [log in to unmask]
Sincerely,
Brian Stumm
>Hello, TechNet....
>
>Soldering (inline convection furnace) BGA's on both sides of a board is
>beyond my own experience, but it seems to violate a principle (at least an
>imaginary one) related to the controlled collapse, or perhaps liquids under
>tension.
>
>For a board design using 3 commercial BGA packages (PBGA 256, eutectic
>balls on 1.27 mm pitch), am I obstinately blocking the path of progress by
>requesting that this package style be confined to only one surface of a new
>board design?
>
>If you are doing this today and it is a piece of cake, go ahead and brag;
>but I would prefer to hear that caution is well advised, i.e. tales of
>misery, shame and corporate disaster resulting from such mistakes. ;-)
>
>
>cheers,
>
>
>
>
>Jerry Cupples
>Interphase Corporation
>Dallas, TX USA
>http://www.iphase.com
>
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