Jonathan,
Not all Sn plating is the same... I have seen reel to reel variations in wetting from the same manufacturer...Your observation of larger grains in the voiding structure is correct and makes sense...But the fact that the device has leads on only 2 sides is probably more indicative of the physical reason it has less voiding...
Because the SO8 is constrained only on 2 sides by solder, during the reflow process the package can tilt front to back and allow the flux and gases to be moved outward from the center ground pad to its edges... This allows the surface tension of the wetting solder to pull the package toward the wetted solder mass on the PCB pad which sweeps out the void forming foreign material in the solder melt...
Normally we run the SO8s with the leads parallel to the axis of the oven..
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of jonathan noquil
Sent: Wednesday, March 02, 2011 6:06 AM
To: [log in to unmask]
Subject: Re: [TN] Solderability of Matte Sn Finish Package
Hi All
Yes we measured the Sn plating thickness by crossection and both packages
seems to be at 10-13 microns (within specs).
The package is QFNX supplier vs superSo-8 from Xsupplier. Both are QFNs
The Superso-8 part almost soldered very well but QFX has almost 90 % voids.
They are soldered side by side using the same conditions as to reflow and
paste.
Is there a compatibility issue with this?
Is the annealing process can affect the solderability when the Sn grain
structure seems to be crystallized?
Maybe the other part (SuperSO-8) dont anneal the Sn plating and the other
QFN anneal it?
We look at the surface comparing by SEM and they are different. The good
solderability has compact grain structure and the bad one seems to be
crystallizing.
Where can i get J-002?
thanks All
On Mon, Feb 28, 2011 at 10:26 AM, Dennis Fritz <[log in to unmask]> wrote:
> Jonathan -
>
> Your problem is exactly why IPC Standard J-002 was developed. Using this
> standard enables you to quantify, before you mount components and have to
> rework, how much difference there is in solderability Sounds like your
> assembly conditions are a very sensitive test for tin plating!!
>
> Denny Fritz
>
>
>
> -----Original Message-----
> From: jonathan noquil <[log in to unmask]>
> To: TechNet <[log in to unmask]>
> Sent: Mon, Feb 28, 2011 8:45 am
> Subject: [TN] Solderability of Matte Sn Finish Package
>
> Hi All
>
> I noticed that there are differences in the solderability of two packages
> mounted on the same board side by side with each other
> using the same reflow profile and paste.
>
> The first package has almost less than 5 % voids of the total area and the
> other package has almost 90 % voiding.
>
> Would there be an effect of the Sn plating quality to the solderability of
> these packages? What are the factors affecting Sn plating quality?
>
> Thanks
>
>
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