|Ask the Experts|
October 22, 2018
BGA Replacement Limit
How many times can a BGA component be replaced at the same location on the same PCB and retain reliability? We are using BGA components with polymer balls on gold plated multilayer PCB's that are 2 millimeters thick.
|Expert Panel Responses|
1. A lot of our customers will count the thermal cycles of the PCB. And based on the PCB material integrity, they determine at what point the PCB become questionable. 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 above. BGA manufactures will normally specify how many times a component can be thermally cycled before the chip within the BGA package is no longer functional, or questionable. 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.
There is no hard industry rule but the rule of thumb for most companies is no more than 5 to 6 thermal cycles at reflow. The adheasive system for the board pads continues to breakdown after 3 cycles and the bga part itself will also start to weaken at 3 cycles so most companies err on the cautious side and only replace twice at the same location after the initial build which is normally 2 thermal cycles for top and bottomside reflow thermal cycles. Then one would have a remove and replace which is 2 more thermal cycles and then possibly another remove and replace which is 2 more for a total of 6 cycles. High reliability hardware normally does not like seeing more than 4. But again this normally customer generated and it differs between companies and the degree of long term reliabity expected. Based on the information given this is a general comment for the number of rework cycles.
VP Engineering Services
STI Electronics Inc.
It depends on many factors; leaded solder will provide you with additional cycles where a lead-free application will reduce the number of possible cycles. If you are adding solder paste to the operation it will help with the reliability of the finished product. Testing and evaluation of your particular application must be performed to confirm the maximum number of cycles for your particular PCB.
Regional Sales Manager
OK International Inc.
I totally agree with Mark McMeens' assertion below that often manufacturers only get as few as two attempts to get it right, but this begs a bigger question, "Why am I reworking my BGAs in the first place?" I believe the answer more often than not has to do with a poor profile. This year I have seen tremendous interest in this area as manufacturers continue to struggle with micro BGA on more complex boards, which is even further challenging for CMs who get 50 boards from a customer who wants 50 boards back. No drilling holes for thermocouple readings under the BGA! I added some additional comments on this subject along with useful information from TC attachment (non destructive) to how to profile BGAs without destroying other more heat sensitive components. http://profilingguru.com/reflow/define/why-are-you-replacing-bgas/
Global Account Manager
All depend of the board finished. We are using AgIm and ENIG-Au/Ni we reworked Ceramic BGA's three times on AgIm boards and five times on ENIG-Au/Ni finished. The BGA removal profile is crucial in order to not damage or burn the PCB lands.Sergio Ilescas Hernandez, Arris Group de Mexico
We have tried the BGA replacement two to three times on the same PCB. And we found it reliable. The only thing that is to be considered to have proper removal of BGA in order not to damage the PCB solder pads.Maninder Singh, Deltron (A Division of CDIL), India
At my company we qualify PCB suppliers in part based on HATS or IST via reliability results. We specify 6 preconditioning cycles to simulate assembly processes. Our reliability test results, then, are only valid up to 6 thermal cycles. As Mr. O'Brien points out, a board with one reflow cycle has margin for only one BGA replacement. So we limit our assembly suppliers to 6 thermal cycles at any one site, but only one BGA replacement.Jimmie King, GE Healthcare
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