Stephen,

My concern with your customer request would deal with
resultant solder joint volume. If the component
vendor's paste volume can be met with out adding any
solder paste then this should be OK.

For CSP's in a repair environment relying on flux only
works well for us.

Hope this helps,

Tony Di Mauro
Quality/BGA Process Engineer
Circuit Technlogy Center
Haverhill MA

--- "Stephen R. Gregory" <[log in to unmask]> wrote:
> 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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