Is Pre-Bake Standard for Rework?

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.

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.

Don is the General Manager of VJ Technologies, Inc., a leading manufacturer of X-ray Inspection and Rework equipment for the electronics manufacturing industry. He has more than 20 years experience in development, manufacturing, and support of a wide range of capital equipment.

Prashant has 15 years experience in design and process development. With a MS in Mechanical/ Materials Engineering his areas of interest are connectors, electronics assembly, SMT, reballing, wire bond.

James Mahoney is a Technical Operations Manager with a 20 year track record in managing new product introduction. He is a skilled leader, motivator and problem solver with a strong background in Product Knowledge and Engineering Management.

Retired - Mr. Bliss has 20+ years experience creating process methods that improve profitability by maximizing hidden unused capacity and throughput. Ken has expertise in all areas of manufacturing specializing in electronics assembly.

EH Lim has been in the PCB Assy industry since 1985, starting at Thomson/Singapore for 5 years before moving to Electrovert Asia Pacifc. Lim was Sales Director for Vitronics Soltec prior to joining ECD in 2007 as Managing Director for Asia Pacific.

Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.

Pre-baking is a requirement for all field failure returns that require rework. If the rework is for an assembly that is still in process, baking should not be an issue because it is still in a controlled temperature and humidity environment. My rule of thumb, if you don't know where it has been, bake it before rework.

I recommend that all assemblies be preheated and to use a hot air pencil to remove the components that need to be removed. When you do not preheat the assembly you are thermally shocking the component and surrounding components and the board assembly in general. If you do not preheat you are cutting corners. I have seen ceramic components crack because of thermal shock. I have seen glass seals crack from thermal shock.

If the rework is concentrated on removing and replacing MSD such as BGAS and CSPs, baking the populated board is necessary in order to eliminate the moisture presence on the assembled board. This is clearly defined and reflected on topic#6 of IPC/Jedec J-STD-033A (Handling, Packing, Shipping and Use of Moisture Reflow Sensitive Surface Mount Devices). However, it is important that the appropriate bake duration for the PCBA and the component to be reworked is considered as per table 4-1 since some PCBs and MSD parts are sensitive to baking.

IPC-7711/21 Rework and Reapair of Electronic Assemblies, and IEC EN 61192-5 RWL of Electronic Assemblies, tell to perform adequate pre-bake boards (PCBA) before rework.

A few thoughts from a pcb manufacturers view with experience in flex-rigid:

Drying conditions are also dependent on the copper layout, big copper areas make drying difficult and should need a much longer drying time.

A very smooth drying could be performed in a drying cabinet but this needs a long time, i.e. a week.

And last but not least Polyimide is not always the same critical material considering moisture intake. There are new Polyimide-glass constructions that have even less moisture intake compared to FR4.

So many divergent views! Do we need to bake or not is still not clear. Can we decide that it is relative to component density on PWA or the type of component being reworked on PWA? What is the impact on other soldered components when we bake the PCB at 105 deg.C?

Mr. LePage has been a key member of the team at Circuit Technology Center since 1996. He has vast expertise, experience and understanding of complex circuit board rework, repair and modification operations. He is one of the most knowledgeable experts in this area across the globe.

With no idea of storage of the assembly, the PCBs need to be baked. Also, moisture sensitive devices need to be baked to avoid any thermal shocks and pop corning. Also, inspect the terminations of the devices before populating into the PCBs.