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April 2011

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 19 Apr 2011 10:48:19 -0500
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Good point, Ben.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Tuesday, April 19, 2011 10:42 AM
To: [log in to unmask]
Subject: Re: [TN] EXTERNAL: [TN] LGA geometry advice

Eric,

Can you increase the individual pad size if the array spreads out?
That would increase the robustness of the joints to offset the increased stress from the joints being further from the center of the part.

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison
Sent: Tuesday, April 19, 2011 11:36 AM
To: [log in to unmask]
Subject: EXTERNAL: [TN] LGA geometry advice

Rights folks!

I'm designing a new surface mount device which originally started off as 
5 X 5 square.

It has 25 I/Os.

It's LGA is a 5 X 5 array of 0.60 diameter pads on a 1 X 1 pitch.

The device has now increased in size to 7.5 X 7.5.

Now, do I increase the LGA spacing to cover the increased area again or 
do I stay with what fitted on the 5 X 5 device? I'm inclined to stick 
with the original LGA as I believe that the stress analysis will tell me 
that the smaller grid will have lower stresses in the SJs than the 
bigger grid.

Are there any practical reasons for maximising grid size?

Regards,

-- 
Eric Christison
Consumer&  Micro group
Imaging Division

STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom

Tel:	+44 (0)131 336 6165
Fax:	+ 44 (0)131 336 6001

The contents of the email are ST confidential.




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