Earl,

As a self-described proponent of flux only mounting of BGA, please help us
understand the impact on product reliability of reduced solder in these
connections.

Dave Fish

----- Original Message -----
From: "Earl Moon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, December 18, 2001 10:51 AM
Subject: Re: [TN] Optimum Method to Apply Solder Paste to PWB's for BGA
Application s?


> Most everyone's business relies on optimizing process management so the
most
> reliable product is effected. If not, what's the point.
>
> For plastic BGA's, coplanarity always was and still is an issue as is CTE
in
> some applications. Therefore, whatever contributes to a reliable solder
> joint must be considered.
>
> I am a proponent of applying only flux to effect reflow under specified
> conditions. Short of that, I prefer using "hard" balls in all four corners
> and reflowing using solder paste thus creating colums that are very
> forgiving as compliant in light of coplanarity and CTE issues. When not
> using hard balls, a little drop of epoxy, carefully thought out and
applied,
> does the same job. Not everyone enjoys this concept.
>
> Now, we move on to CBGA's requiring paste applications though CTE issues
now
> become equally critical but in reverse in some cases. CCGA's are about as
> good as you can get because all aforementioned issues are resolved but for
> one. Where do you get these but from IBM.
>
> uBGA's offer considerable advantages on both counts concering coplanarity
> and CTE matching characteristics. Sure are small though.
>
> Ah yes, about solder paste: How can you not use it but in low volume,
> critical applications where flux will do?
>
> Many have stated the obvious as using appropriate design rules. These may
> consist of using 10% smaller pads than balls then designing stencil
> apertures to overprint paste 20% - and on it goes notwithstanding aperture
> shapes as square, diamond, or round. I get along with round very well.
>
> Not to get carried away, but you know I will, but considerations for the
> type connection using dogbones is another factor. Don't do right angles.
Go
> right to the connection and don't forget rework/repair/modification
> requirements. Now it's time to say and on it goes.
>
> MoonMan
>
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