Bob,
Good Luck! You'll need it. Using 0.5% bow and twist will help but more importantly you'll need to address the proximity of the rivets to the ceramic capacitors. Our current philosophy is to place 1210 or larger (especically 1812) caps no closer than 0.500 inches from an edge, cut-out, press-fit connector, or screw.
Regards,
George
George M. Wenger (908)-546-4531
Reliability Engineer
RF Power Amplifier Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: Crain, Bob [mailto:[log in to unmask]]
Sent: Tuesday, January 06, 2004 8:22 AM
To: [log in to unmask]
Subject: [TN] Mechanical stress on ceramic chip caps
We build boards for space and they must be bonded and riveted to rigid
aluminum frames to withstand the environments. We currently specify the
IPC-6012 requirements which are 0.75% bow and twist.
There is a concern that we may need to specify 0.5% bow and twist to prevent
1812 and possibly 1206 ceramic capacitors from developing cracks after the
boards are attached to the frames.
With our boards, .75% translates to a maximum of 45 mils of bow and twist.
Any thoughts on problem areas?
The boards are normally .090 thick, 8-12 layers and polyimide.
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