There are reworkable epoxy fluxes / no-flow underfills that are designed to come off during rework and not damage PCB pads Indium Corporation makes reworkable no-flow underfills (NF-260) / epoxy flux (PK-002)
Karthik Vijay
Technical Manager - Europe, Indium Corp.
Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.
The answer to this question really depends on whether you are talking about a component simply "glued" to the PCB with a small dot of adhesive or a component which has been encapsulated on the PCB. Either way, check IPC 7721 section 2.3.1 for identification and recommended removal procedures of coatings. 2.3.1 and the subsequent sections describe the removal procedures, from simple scraping to chemical to abrasive blasting (Micro blasting) of the coating for removal. All of the procedures are developed with the goal of no damage to the PCB or the component. In the first instance, an adhesive dot holding the component, the heat from the removal of the component should be sufficient to over-cure the adhesive. Once the solder joints have all reflowed use a gentle twist to break the adhesive bond. Beyond that, the remaining adhesive can be removed with a gentle scraping or additional heat and scraping. The second situation, where the component is completely or partially encapsulated is a little more challenging. The first order of business is to check with the manufacturer of the epoxy and find out what they recommend for removal procedures. Some epoxies can be removed with a solvent and others use heat. A controlled application of the heat or solvent will be the key. IPC7721 section 2.3.1 can also be used to determine the generic type of coating. As stated in 7721, there are 5 general types of coatings. Acrylic resin, Epoxy resin, Silicone resin, Polyurethane resin, and Paraxylylene resin. Once you have determined the method for removal, you can follow the procedures in IPC-7721 sections 2.3.2 through 2.4.2 to complete the removal of the coating. Once the coating is off, it is a simple matter of removing the component through desoldering as appropriate.
Kris Roberson
Manager of Assembly Technology, IPC
Kris Roberson has experience as a machine operator, machine and engineering technician and process engineer for companies including Motorola, and US Robotics. Kris is certified as an Master Instructor in IPC-7711 / 7721, IPC A-610 and IPC J-STD 001.
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