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October 10, 2018

Rework for OSP Assemblies

Should we modify any rework or repair procedures for circuit board assemblies fabricated using OSP (Organic Solderability Preservative) bare circuit boards?

J.N

Expert Panel Responses

I would use a slightly more active flux and clean offany residue remaining with a good cleaner. This should give you a better chanceto wet the copper if it has aged and oxidized. If the PCBs are straight offproduction and need rework then you should be OK with standard no-clean wires.

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Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

Accordingto Enthone, the manufacturer of the Entek Plus 106A OSP coating, the coating ismore susceptible to certain types of "solvents" than others. They statethat alcohol will strip about 70% of the coating, water will remove about 15%,but Kyzen Lonox only about 3% of the coating. Picking an appropriatesolution is key to prolonging the life of the coating. In the event thatthe coating is stripped using alcohol or other classic solvents, they recommendthat the soldering be completed within 12 hours. Fitting the proper washmaterial as well as a limit on time between the soldering would be applicableto the repair / rework process. Once solder has been applied to the pads,the repair or rework process should not need to be modified.

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Matt Stevenson
Director of Marketing
Sunstone Circuits
Matt Stevenson has over 20 years experience in the PCB industry. Serving in roles as a Chemical Lab Technician, Process Engineer, Quality Engineer, Quality Manager, and Marketing Manager. He has proven himself to be an invaluable resource.

I can think of one scenario where procedures might need to bemodified; when rework needs to be performed on the first-assembled side of atwo-sided SMT assembly, care needs to be taken not to degrade solderability ofthe second-side pads. This would be of concern where a BGA or otherbottom-terminated component is to be reworked, since repair stations canaggressively heat the opposite side. You would need to evaluate the effects ofthe rework station on solderability, or alternatively do rework only aftersecond-side reflow. The second option may be less than desirable, depending onthe design. If your assembliescontain through-hole parts that need to be soldered after reflow operations arecomplete, you should also take care that heat from rework does not degradesolderability in these areas.

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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

OSP (Organic Solderability Preservative) boards havebeen around for many years. As to whether the rework or repair process shouldbe modified, I would not think so. One thing to consider is the solderabilityof the board after a period of time after their manufacturing date. The OSPcoating does have a shelf life and to repair the product by removing andreplacing components might require a more aggressive flux. If a more aggressiveflux is used then a cleaning process must be incorporated and a check ofcleanliness is strongly suggested. So other than using a more aggressive flux,I don't see the need for any additions or modifications in the process.

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Reader Comment
OSP is a coating that protect copper. Once you install the components, pads are soldered and tinned. When exist the needing to rework components, an uninstallation will take place, which involves removing the component and absorbing the remaining solder residue on the pads. Therefore, from this perspective, we can understand that pads are tinned so it would not be copper exposed, actually it may contain better solderability than the original form of the pad with OSP. I do not consider it necessary to make any procedure change because the tinning of pads is to increase solderability.

You can make tests with the approved flux of the original process and if it does not give negative issues, use it, but if it results in a negative issue, you will need to make a flux change that does not affect the solder mask or adjacent surfaces.
Luis Alberto Garcia, Sinectech Training