Paul,
Joint strength is not the issue in any case. It is creep-fatigue of the SJs and that comes from the thermal expansion mismatch of the die inside the LGA and the FR-4 PCB. And remember, even so-called benign environments, like consumer products can see delta-T's of up to 80 C [-20 in winter outside to 60 C inside a car], but even Summer use [20 C to 60 C] results in delta-T's of 40 C.
Werner
-----Original Message-----
From: Paul Edwards <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, 16 Apr 2009 1:11 pm
Subject: Re: [TN] LGAs in a military environment?
Graham,
We don't and we don't even recommend it for commercial apps...
BUT... AGAIN... It all depends ...
You might want to use it in a none-critical redundant secondary system...
But even then with care...
Apart from the issues already mentioned... The critical element that the solder
joint is a surface adhesion only joint whose quality can not be determined
without damage to the joint... Yes you can x-ray it or use acoustical microscopy
to determine the voiding but this will not determine the joint strength just
that you have maximized the joint surface area...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, April 16, 2009 3:32 AM
To: [log in to unmask]
Subject: [TN] LGAs in a military environment?
Hello Technet!
One of our designers is advocating using a LGA component in a military
product. Anyone out there doing it? I'm wondering (worried) about the
reliability since it has a very low standoff. And cleaning issues?
An example of the parts I'm referring to:
http://www.linear.com/designtools/packaging/lga/05081807_a_lga66.pdf
A Linear Technologies p/n LTM4604
regards,
Graham Collins
Halifax Production Engineering
(902) 873-2000 ext. 6215
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