Monthly Archives: August 2016

  • Epoxy Bonding Problems on RoHS Boards

    epoxy bonding rohsIf 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

    To find the best epoxy solution for your application shop GoKimco.

  • Surface Texture on Solder Joints after Reflow

    surface defects reflowSeeing surface effects when using lead-free solder is not an unusual occurrence. There are many factors that could be causing texture on the solder joints after reflow.

    The following are several of the more common factors that could be contributing to this defect:

    • Thermal profile used, peak temperature and cool down rate
    • Metal finishes on the parts that were soldered, dissolution occurs which can impact color
    • Reflow atmosphere
    • Physical or chemical properties of the flux, some fluxes react more with the solder surface than others
    • Flow properties of the flux during the reflow process, some fluxes flow more rapidly than others, giving extended exposure to oxygen
    • Excessive oxidation of the parts to be soldered
    • Shelf life of the paste or how the paste was handled prior to use

    Keep in mind that while the surface of the board may look frosty, discolored, or be demonstrating shrinkage effects this does not necessarily point to a reliability issue. Instead the solder joint may remain in excellent working condition with adequate intermetallic bonding.

    If you suspect that there may be a reliability issue associated with the appearance you will need to do some pull/shear testing to examine the bond layers. Use a quality pair of shears for the most accurate results. (http://gokimco.com/search?form_key=ViRkrOmJrsyABtEG&q=shear) If there is a problem with the bond layers, examining the reflow process for problems and / or changing to a different solder paste can correct the problem.

    GoKimco has a wide variety of solder pastes so that you are sure to find one that will sort out this issue. Visit http://gokimco.com/solder-flux-mask/solder-paste.html.

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