Thank-You Mike, noted your points and much appreciated. We will follow up with some measurements.


Thank-you
Mumtaz
858-795-0112
Peregrine  Semiconductor


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Wednesday, September 16, 2015 9:09 AM
To: [log in to unmask]
Subject: Re: [TN] Solder paste print thickness vs. reflowed thickness for SMT packages

As Joyce and others have indicated, there are too many variables to answer your question specifically.
Almost all type 3 stencil grade pastes will contain 50% +/- by volume of metal. [The variance in weight %  for different alloys e.g. Sn63 and SAC is to keep the volume the same according to alloy density.] The theoretical height is therefore 50%. In practice it won't be, variables being transmission efficiency of the specific paste you are using.(Modern pastes are significantly better in this respect than most older/established types). Stencil type, quality and thick/aspect ratio, your board and your print parameters and so on. 45% as mentioned below equates to overall transmission efficiency for the process of 90%, that's not bad. Again as indicated, for these reasons if you want more accuracy than the guidelines offered you will have to measure.

Regards

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, September 15, 2015 10:17 PM
To: [log in to unmask]
Subject: Re: [TN] Solder paste print thickness vs reflowed thickness for SMT packages

(1) flux loading - and type of flux, no clean got low residue and no residue type, the transfer efficiency also play a role
(2) package type and lead geometry/surface finishing type also play a role
- including wetting characteristic of the lead
(3) best is to laser scan the print paste thickness and cross section your pwa in some area and get few package style for your application - your own database (better use for old paste that may have questionable transfer efficiency, especially, small aperture type).
my 2 cents.
     jk
> Dear All,  Does anyone have estimates ,measurements or  correlation
> for printed paste thickness ( lead free- No clean) vs reflowed paste
> height for the 5 mil and 4 mil  paste print thicknesses.
>
>
> Thank-you
> Mumtaz
> 858-795-0112
> Peregrine  Semiconductor
>
>
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