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.

Neil O'Brien Sales Director, Finetech 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 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.

Mark McMeen VP Engineering Services, STI Electronics Inc. Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.

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.

Edward Zamborsky Regional Sales Manager, OK International Inc. Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

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/

Brian O'Leary General Manager of International Sales, KIC Brian O'Leary is responsible for KIC's international customers and distribution in Latin America, EMEA, Russia, India, Australia and New Zealand for the thermal management and process control portion of the electronics assembly and packaging processes.