In a message dated 05/03/2000 8:00:20 PM Central Daylight Time,
[log in to unmask] writes:

> Hi All
>
>  I was hoping I could draw on your experiences
>
>  We have a customer who is convinced that the BGA to be soldered to his
board
>  should be processed without any paste deposit, just gel flux and rely on
the
>  solder ball providing enough solder to form a reliable joint.
>
>  The process would be Paste print, Gel Flux dispense, part placement then
>  reflow.
>
>  We have successfully reworked BGAs using just Gel flux and a Sniper rework
>  station, but I have never processed a BGA through a reflow process using
>  just a gel flux.
>
>  Any comments on potential non-conformances, experiences using such a
>  process?
>
>  Any help would be appreciated
>
>  Clayton Gardner
>  Engineering Manager
>  AEMS
>  11-13 Fiveways Blvd
>  Keysborough VIC 3173
>  AUSTRALIA

 Hi Clayton!

Does he give any reasons for this? I've seen some posts regarding this,
mostly asking the same question that you are asking. But have not read any
reasons that rule one way over the other.

From my experience, I've always used paste...when doing BGA or MicroBGA. To
me it seems to be a more robust process...I could be wrong.

I like the fact that you have fresh soldering material to complete the joint,
instead of relying only on the balls to give you the joint you need.

Also the paste gives you the self-centering characteristics that I'm not sure
a flux will provide. As long as the balls are in the paste, surface tension
of the molten solder during reflow will align everything. I don't know if
flux will do the same thing...I'm suspecting it will not.

Using flux only, from what I know, is done when reballing BGA's, not for
assembly on the PCB....

I expect that there will be differing opinions...

-Steve Gregory-

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