Remember though that the paste from the ball is only relevant if the balls
are of 63/37 construction.  Many balls are 90/10 and will not flow with a
standard profile.

BS



                    Guy Ramsey
                    <gramsey@ACIUS       To:     [log in to unmask]
                    A.ORG>               cc:
                    Sent by:             Subject:     Re: [TN] BGA Production
                    TechNet
                    <[log in to unmask]
                    RG>


                    06/04/2004
                    01:28 PM
                    Please respond
                    to "TechNet
                    E-Mail
                    Forum.";
                    Please respond
                    to Guy Ramsey






You need enough paste to provide good fluxing action. The quantity of added
solder is small compared to the volume of solder in the ball. It is not
relevant if you are working to Class 1.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dacia Super
> Sent: Friday, June 04, 2004 1:21 PM
> To: [log in to unmask]
> Subject: [TN] BGA Production
>
> All -
>
> I am in the process of trying to get a feel for what the
> industry standard (or even personal gut feels are) regarding
> the production of assemblies that require BGA parts.
>
> For example, within our organization, we have recently had
> some interesting debates related to the old school philosophy
> that more paste is always better in production versus the
> opposite philosophy of less is better because it drives
> tighter placement tolerances and a better solder joint with
> the BGA ball.
>
> So, at this point, I am trying to figure out the best
> direction in which to drive our manufacturing processes.
> Seeing that I am certainly in the infant stage of BGA
> knowledge, I figured that I would pose the following
> questions to the 'Net:
>
> Assuming standard eutectic solder:
>
> 1.) If the BGA pad dimensions on a PCB are, say, 16-mils, do
> you recommend cutting stencil aperture size to be greater
> than the pad size (say, 17-mils), cut the aperture exactly
> the same size as the pad (an exact 1 to 1
> ratio) or do you recommend a slight undercut (say 15-mils)?
>
> 2.) Do the actual production equipment pieces dictate the
> solder amount?
> Example, say one manufacturing line is antiquated equipment
> versus a different line that has newer equipment?
>
> 3.) Assuming Class 1 BGA components are built into the
> process (example, parts may have already built in voids in
> the outside of the BGA balls - but clientele and pricing
> allow this to be acceptable), will extra paste in this case
> be better - will the additional paste reflow into the assumed
> outer voids and make a more solid connection?
>
>
> Appreciate all responses.
>
> Thanks -
> Dacia
>
>
> Avant Technology - OEM Module Services
> [log in to unmask]
> Dacia Leanne Schoolfield
> Quality Manager

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