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To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Re: I won't do BGA's
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Comments: In-reply-to Bob Paddock <graceindustries AT gmail DOT com>
   message dated "Mon, 28 Nov 2011 10:07:20 -0500."
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Date: Tue, 29 Nov 2011 22:02:58 +0100 (CET)
From: karl AT aspodata DOT se (Karl Hammar)
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Bob Paddock:
> On Mon, Nov 28, 2011 at 5:20 AM, John Griessen <john AT ecosensory DOT com> wrote:
> > On 11/28/2011 01:59 AM, Karl Hammar wrote:
> 
> [Don't see Karl's message in my email.]
> 
> >> I won't do BGA's
> 
> BGA's are still better than LGA's or even QFN's.
> 
> The latter are a nightmare to get the flux out from under if your aim
> is ultralow current, and want a service life of years.
> 
> Some parts, Accelerometers for example, leave you with few package options.


An article ("Lokala föroreningar ger problem vid ytmontering") in
"elektronik i norden" [1] references a report [2] where they have
mounted QFN's 25, 50 and 75 um from the FR4 base.

At 25um there was remains from all tested fluxes.
At 50um water soluble and one of three "no-clean" fluxes left no traces
At 75um no fluxes was left after washing

The above is for PbSn.

There is a reference to [3], which is said to show that with suitable
layout one can get a stand-off distanse of 75-100um.

Regards,
/Karl Hammar

[1] http://www.elinor.se/

[2] M. Bixenmann, M. Kontrd
    Cleaning for Reliability post QFN-rework
    SMTA Inernational Conference 2009
    pp 766-781

[3] Dong Hyun Kim et al.
    Reliability Stydy and AF-modelling for SnAgCu- and PbSn-solder joints in QFN packages
    SMTA Journal, vol. 23, issue 1, 2010

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