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August 27, 2012

How to Remove Adhesive Bonded Resistors

How to Remove Adhesive Bonded Resistors
We have a board that was originally built using an adhesive and probably a wave solder process. We need to rework some of the resistors on the board and are not sure of the method to remove them. Using two soldering irons we can quickly melted the solder, but the parts do not come off the board. Any suggestions for removing the resistors? We have hundreds of resistors to remove.


Experts Comments

A "hot tweezer" adapter for a soldering station probably will do the trick for removal. It will heat both joints and the component can then be gently rotated to break the adhesive bond and lifted. Alternatively, a hot air gun can be used to heat the component and reflow both joints, and a tweezers can then be used to gently twist the component to remove it. Any process that you use needs to be qualified to set the process parameters such that the PWB and surrounding components are not damaged. When reworking multilayer ceramic chip capacitors, I suggest a hot air process to minimize thermal shock, especially for larger components.
Fritz Byle
Process Engineer
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.
I would suggest the use of Thermal Soldering Tweezers. This tool features two heated points in a tweezer configuration. The heated tips will reflow the solder joint on both sides of the chip simultaneously and allow you to grasp the chip with security. Once the soldering has fully melted you can give the chip a slight twist to break the glue joint and lift the chip from the board.  

IPC 7711 method 3.3.2 lists the full, step-by-step procedure See: IPC-7711B-7721B_Chip_Component_Removal_Tweezer_Method.pdf
Kris Roberson
Manager of Assembly Technology
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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