Phil,
Thanks.
It is leadfree solder paste-SAC305 with 89% metal loading.
We need the solder bump for secondary process which is hot bar soldering.The
bump is almost a dome(both side curvature) shape.We can't keep the bump
height consistant and here I am trying to see if there is any formula for me
to determine the bump height.
The final appearance is always a bump surrounded(like an island) by flux
residue.
Thanks again for sharing your experience.

rgds
sumxp


----- Original Message -----
From: "Phillip Bavaro" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 02, 2005 1:54 AM
Subject: Re: [TN] solder bump height formula


> Hi Sumxp (couldn't bring myself to say hi no name....!),
>
> What is the percentage of solder in your formulation?  And is it lead free
or Sn 63?
>
> You know the deposited volume before reflow and can calculate the volume
after the heating process.  Typical numbers for 5 mil thick stencils with
Sn63 are 40% of original height, and I will admit it has been a long time
since I have printed 8 mils thick.
>
> My maximum print height limit for a 5 mil thick stencil is 6 mils which
yields approximately a 2.4 bump after reflow.   It is never flat so be aware
of this.
>
> The wetting characteristics and shape of the pad can raise this number as
high as 3 mils in my experience.
>
> The true height of the bump will also depend on the flux characteristics
(whether or not it completely runs off the molten solder or puddles on top.
>
> If you have a component lead sitting on the paste, this will lower the
thickness of the solder below the lead due to the solder wicking up onto the
lead.
>
> Good luck,
>
> Phil
>
>
> No Name <[log in to unmask]> wrote:
> Hi,
> Is there any formula to calculate the after reflow solder bump height?The
> land size is 123*63mils with 1:1 stencil opening and using 8mils stencil.
>
> regards
> sumxp
>
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