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November 2005

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From:
Joyce Koo <[log in to unmask]>
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Date:
Tue, 8 Nov 2005 09:25:18 -0500
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here is my take on this: commonly known products family:
(1) PC work station (office): MFG +25 to 260 C (leadfree, with limited
exposure at 260 = usually <30 sec)
                        storage -40 to + 85, operation 0 to +55,
                        Real Testing: -40 to +125
(2) Auto or other similar production: MFG +25 to 260
                        storage -55 to 125, operation -40 to 125
                        Real testing: -55 to +125, device -55 to 150
(3) Mil stuff or other special application: MFG +25 to 260
                        sotrage -62 to 71, operation -40 to 125
                        Real testing: -65 to 150 (cycle), device -65 to 150 (shock)
As for the price of the stuff, (3) = 10x (2), and (2) = 5-10x (1)
If you qual by the (3), you should be OK for (1) and (2).  Qual by
similarity or over qual... but you pay a lot for the material and design...

Well, look like your material selection or design is not suitable for the
test condition you have been specify (crack this or crack that)... The test
condition and application must been known prior to design and BOM... you can
not upgrade from (1) to (3) easily...Doug Paul, shall we recall some old
"de-rating... up-rating" fun days?  One story is someone have to put a key
device (qual No. 1) into a thermal insulated box in order to upgrade the
board to meet the (3) test condition....hehehe, a lot of fun...

               my 1.7 cents..jk


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Babcock John
Sent: Monday, November 07, 2005 7:29 PM
To: [log in to unmask]
Subject: [TN] Temperature Cycling


Does anybody know of any special considerations on circuit boards for
temperature cycling.  We are testing the board to -65C to +85C.  We are
seeing via barrels cracking and TH connector solder joints cracking.  Do
we need to add extra pad area?  Just curious if there is an IPC document
on cold temperatures or temp. cycling and causing stress on the circuit
boards.

Thanks!

John Babcock

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