If you have seen problems with epoxy bonding components to RoHS circuit boards, you are not alone. This may be related to the surface energy of the board. Generally high surface energy is a good thing, while low surface energy is detrimental. The surface energy of the solder resist varies with the many types available. Oven curing the solder resist tends to lower the surface energy because the silicones are then forced to the surface during the curing process.
It may be useful to perform a simple control test to investigate the surface energy of the boards. This can be done using dyne pens or a contact angle test. If you are using a dyne pen, 36 to 38 dynes is average. A no-clean, assembled board would be about 32 dynes, and you would not want to work with anything lower than this.
To perform the contact angle test, measure the contact angle of a droplet to see how much the droplet beads up or wets out onto the surface. If when you perform the droplet test you find that the beads are quite round and do not wet this indicates low surface energy and poor bondability.
From here you should conduct a suitable gas plasma treatment on some of the boards and see if this improves bondability and adhesion. You can bond actual parts to both the control and plasma treated boards to confirm any improvement in adhesion.
If you are bonding to a metal surface, you should always first prep the surface with etch or alcohol. This will ensure the area is clean prior to any epoxy applications. GoKimco offers a complete lining of cleaning wipes to prep the area. Visit
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