December 2020
PCB Rework of Conformally Coated PCBs
Conformal coating is used on PCBs to protect them in their operating environment from chemicals, moisture, dust and temperature. The coating layer is a few thousands of an inch in thickness. Their makeup falls into a broad variety of categories including but not limited to epoxy, silicone, urethanes and acrylics. Once the board is assembled and tested the coating is applied. If removal and replacement of components is required the conformal coating must first be removed in order to mechanically detach the component from the assembly prior to removal.

Conformal coating removal can be challenging as there are several methods as well as associated risks involved with removing the coating prior to rework. Chemical removal may harm components or board materials. Heat, abrasion or mechanical force applied to the coating may damage components or the physical attributes of the PCB. In addition to the damage caused by the removal of the coating the rework process itself may cause soldering anomalies on the PCB. Areas in and around the rework area, when heated, may cause the solder to “squirt out” from the underside of the leadless devices or BGA packages causing electrical failures.

BEST has a vast amount of experience in working with conformally coated printed circuit boards being able to determine which of several methods are the best-suited for the rework job at hand.
If you have a PCB rework project on a conformally-coated PCB do not forget to call Laura at 847.797.9250 or send her photographs at lripoli@solder.net.
Large Footprint Device Rework
Large footprint packages (greater than 50mm x 50mm) are a challenge to rework as there are many potential pitfalls in reworking these large components. Developing a removal profile that is consistent across the entire package can be a problem in that neighboring devices can be damaged by longer than usual profiles.

In addition, getting a very small temperature difference difference across such a large area can be especially troublesome for hot air nozzles unless they are well-designed. Large differences in temperature across the package will cause the solder to reflow at different times thereby causing warping of the package. IR is a better reflow source for these applications. Also difficult is inspection as many times these larger BGAs or sockets can be visibly inspected along the periphery rows but not to the center of the device. This mean inspection will rely on more sophisticated x-ray imaging.

BEST recently had a project for a 51 x 76mm socket. Our engineering team was able, with the use of a profile board, to optimize the various process variables in order to get a good-yielding rework. We invite you to call BEST if you are having difficulty reworking these larger devices.
What’s in the New J-STD-001 Rev H?
With the release of the latest revision of the J-STD-001 come several new items that are are of significance. Included in the list of significant changes found in the J-STD-001H are the addition of a section on the inspection of solder joints using x-ray analysis, updated terminal wrap requirements and the inclusion of updated cleanliness and residue measuring requirements on the impact of the PCBs’ reliability.

The last of these items will be unpacked for you in the above video. Training materials will be released some time in 2021. In the mean time contact JL@solder.net to schedule your next IPC J-STD-001 class.
Message from Dan - Happy Christmas
Wishing you all of you a Merry Christmas and a Healthy Happy New Year.

Thanks for your support in 2020!
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