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March 2003

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Subject:
From:
Dougal Stewart <[log in to unmask]>
Reply To:
Dougal Stewart <[log in to unmask]>
Date:
Mon, 3 Mar 2003 13:56:16 -0000
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text/plain (66 lines)
I would suggest
 1.yes, not only to make assembly easier, but also to enable probing at BBT
less hit and miss, and don't forget to add a small extension to the pads to
show under Xray inspection that the solder reflowed completely
2.yes, High Tg FR4 should stand up to the thermal stress, all other things
being equal (plating quality etc), but not all the High Tg materials perform
the same. You could always add IST coupons and compare different materials
to find the one that suits your purpose

Dougal Stewart

email:  [log in to unmask]
phone: +44 1896 822204
mob:    +44 7984 629667
www.pwbsolutions.co.uk
----- Original Message -----
From: "Ofer Cohen" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, March 03, 2003 12:16 PM
Subject: [TN] Finish and material


> Hi, folks,
> I have two questions of a layman, regarding PCB 0f 22 layers, 3.4 mm thick
> (controlled impedances in all the signal layers, what else?):
> 1.      Until recently I succeeded to protect the fortress and avoid using
> BGA with pitch of less than 1 mm. Lately I missed a battle, and a 0.8 mm
BGA
> was implemented. Does it necessarily mean that I have to leave my old and
> favor HASL finish and migrate to the immersion field?
>
> 2.      Will FR4 (of course - Tg=180 deg C) withstand the thermal stresses
> of this stack up, or should I migrate to more stable material (lower Cte-z
> axis)?
>
> Regards
> Ofer Cohen
> Quality Assurance Manager
> Seabridge Ltd.
>
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