Number of times reworking

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How many times can a populated board been reworked? What can... - May 26, 2003 by bayanbaru

Much of the ability to survive rework or thermal excursions ... - May 27, 2003 by davef

Can I then say that in general boards are not encourage to r... - May 27, 2003 by bayanbaru

That's what we do [no more than three reworks or mods]. You... - May 28, 2003 by davef

bayanbaru

#24596

Number of times reworking | 26 May, 2003

How many times can a populated board been reworked? What can go wrong (reliability) if the populated board is reworked more than 4 times?

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davef

#24602

Number of times reworking | 27 May, 2003

Much of the ability to survive rework or thermal excursions is dependent upon the fabrication materials.

The board qualification criteria under the 55110 was designed around 5 thermal heat cycles.

Consider reworking a BGA in this context. BGA interposer heat cycles are: * Initial balling * Assembly * Component removal * Site preperation * Reballing * Component replacement

Board heat cycles are: * Assembly reflow (2 - 3 times) * Component removal * Site preperation * Component replacement

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bayanbaru

#24609

Number of times reworking | 27 May, 2003

Can I then say that in general boards are not encourage to rework more than 3 times since the boards will be subjected to Top and Bottom reflow? What is 55110?

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davef

#24613

Number of times reworking | 28 May, 2003

That's what we do [no more than three reworks or mods]. Your "four reworks permissable" was probably based on the 55110 five thermal cycles, counting wave soldering as the first cycle.

How do you plan to keep track of each of those rework actions?

For printed circuit boards or printed wiring boards where MIL-PRF-55110 (formally MIL-PRF-55110) or MIL-P-50884 is cited, DSCC recommends that MIL- PRF-31032 be used. MIL-PRF-55110 is inactive for new design after December 31, 1997 and has been replaced by MIL-PRF-31032. MIL-P-50884 will become inactive for designs and replaced by MIL-PRF-31032. Since there currently is no equivalent document for the cancelled MIL-S-13949 (formally MIL-P-13949), DSCC recommends that the contractor have a method of assuring that laminate materials used in conjunction with DSCC contracts be at least equivalent in quality and reliability to that which was available prior to the cancellation of MIL-S-13949 on 11/30/98.

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