Most of the models that have been developed can take care of the variables you mentioned—if not directly, then in terms of their influence on measurable parameters such as effective CTE, SJ height, etc. IPC-SM-785 was written to free people from the need to to testing ad infinitum with every new component that comes along.
Werner
-----Original Message-----
From: Post, Scott E <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, 16 Apr 2009 9:27 am
Subject: Re: [TN] LGAs in a military environment?
There are too many variables at play to make blanket statements. What
die size, paste stencil thickness, board material, Pb free or SnPb, mold
compound, temperature cycles (ramp & dwell times, temp extremes), are
the signals near the die edges active or redundant, etc? I've done a
good bit of thermal cycling of leadless devices like MLF/QFN and LGA
(mostly -40/+125C) and have found that reliability is very device
dependent - sometimes in very counterintuitive ways. Some last a couple
hundred cycles and some go for thousands. I've been surprised enough
times that I've resigned myself to building coupons and performing
thermal cycling when new ones come along. Although if I got organized I
could turn the Weibull plots over to our modeling guys and save myself
some future work.
A long winded way of saying, "it depends". Sorry.
Scott Post
P.O.U. 1130-OK14-FABIII
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
0A-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, April 16, 2009 6:32 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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