Ask the Experts
April 20, 2009
Component Rework Limit
What is the maximum number of times allowed to rework the same component on a circuit board? Is there a maximum limit for the total number of components reworked on one circuit board?
I have looked thru IPC-610, IPC-7721 and J-std-020 and cannot find a reference.
Expert Panel Responses
Most customers will consider the thermal cycles of the PCB and component in question. Based on the PCB material integrity, they determine at what point the PCB become questionable. I will use a BGA as an example.
1. Consider the thermal cycles for the PCB:
a. Placing and soldering a BGA equates one cycle.
b. Removing the BGA is the second cycle
c. Cleaning the site of is the third cycle.
d. Soldering a NEW BGA is cycle #4
So the question becomes, do you want to go thru these cycles again? Is the thermal cycle for EACH step consistent? The answers may not be a simple "Yes" or "No", and may include data that supports reliability test data that provides proof that a PCB can withstand X amount of thermal cycles before the material degrades and becomes a liability.
2. Recycling a BGA (reballing) is similar to the cycles above. BGA manufactures will normally specify how many times a component can be thermally cycled before the die within the BGA package is no longer deemed reliable. Of course, component cost and the volume of rework needed is also a consideration in deciding the best process to follow.
Although the solder is a key aspect of successfully soldering a component multiple times, that is only one of three critical areas that need to be considered. The PCB and the component themselves need to be fully understood and should be tested throughout the process in deciding how many times a rework cycle can and should be used.
Neil O'Brien has worked in the field of electronic manufacturing equipment for over fifteen years and is currently Sales Director for Finetech, a manufacturer of precision rework systems and die bonders.
There are too many variables involved with any decision about how many times an assembly or a specific connection can be reworked or repaired.
Some examples are immediacy of need, age in projected life cycle, criticallity of function, operating environment, cost of replacement, cost of rework/repair, or availability of alternate assembly. While it has been shown in numerous reliability presentations that every thermal cycle degrades the overall assembly shortening life, only the user knows the projected life cycle.
Some assemblies may be robust enough to withstand many thermal (reflow) cycles before being so degraded that reliable function is a concern, and there are other assemblies or components that aren't capable of withstanding any additional thermal (reflow) cycles.
The new Revision B to IPC-7711/7721 has this statement in the Scope: "This document does not limit the maximum number of rework, modification or repair actions to a Printed Circuit Assembly."
Director - Certification & Assembly Technology
Mr. Crawford is Director of Certification and Assembly Technology for IPC. He is technical liaison to the IPC committees that maintain critical industry standards and has presented numerous papers internationally.