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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