Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Number of thermal excursions per componet

Frank

#7090

Number of thermal excursions per componet | 27 June, 2001

I'm interested to know the guide line , or standard or evaluation methode of how many total parts per board allow to be changed and how many times a single location can be changed. Any other refinements you might have are of interest as well.

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#7099

Number of thermal excursions per componet | 27 June, 2001

Let�s break this down to get started.

SOLDER CONNECTION: No documentation of the degradation in the fatigue life of a fine pitch solder joint after rework. If you do the rework properly and not too often, there is no degradation in the fatigue life of solder joints after rework.

PRINTED BOARD: Degradation of surrounding solder pads and/or PTH/PTVs with multiple heat cycles is well documented. We allow three repairs / reworks of a board. J-STD-001 talks to the issue of process indicators and the need to proper document / MRB all rework / repairs.

COMPONENTS: Huge room for variation. For instance, Motorola ships no product with reworked BGA. Others routinely replace the balls and re-use the BGA. [Here�s a take on Motorola�s thinking on repairing BGA. As a minimum => BGA Cycle 1: solder ball attach. BGA Cycle 2: BGA attach to board. BGA Cycle 3: BGA removal from board. BGA Cycle 4: BGA pad dress. BGA Cycle 5: BGA ball replacement. BGA Cycle 6: BGA re-attach to board. Board Cycle 1: BGA attach to board. Board Cycle 2: BGA removal from board. Board Cycle 3: board pad dress. Board 4: BGA re-attach to board.]

ECO: Two classes for PWBs and assemblies. * "Lower" class refers to in-house standards, DIN IEC 359, and DIN IEC 326 * "Higher" to MIL-P-46843, -P-55110, -STD-275, -STD-454, and DOD-STD-2000-1 to -4. Jumper wire procedure itself is from 1991, but has not been updated to newer standards. "Lower" class has the following rules: * Max numbers of ALL repairs, added components, jumper wires etc. PCB size in cm^2 number LT 100: 5 100-300: 10 300-600: 15 GT 600: 20 Jumper wires and added components LT 100: 3 100-300: 6 300-600: 9 GT 600: 12 "Higher" class allows no repairs.

BARE BOARD REPAIR: IPC-6012A with Attachment #1 - Qualification & Performance For Rigid Printed Boards states "as agree upon between the user and the supplier �", but goes on to suggest a guideline of "no more than two circuit repairs for each 0.9 m2 or less of layer area per side."

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