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Thread: Adhesion on overmolded PCB with PA 678

  1. #1
    Join Date
    Dec 2012
    Location
    Serbia
    Posts
    102

    Adhesion on overmolded PCB with PA 678

    Hi all,

    I have big problem during overmolding of some PCB. Main function of molded part is to make part waterproof.
    When molding is finished, resaults are good, but after day or so there is separation (picture). We have problem on around 30-50% of total number of parts.
    Click image for larger version. 

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    Material for overmold is PA 678 (macromelt), material for PCB is polyamide.

    So far I tryed every speed and pack profile, different temperature profiles of tool and resin, increasing of gate, cooling time up to 5min (just for testing), tool opeining profile, material drying on diffenet profiles....
    In summary i changed every parameter from lowest point to higest point, and i didnt got any solution.
    Anyone have experience or advise what i can try next?

    P.S. Tool and parts are cleaned from greasses, worker have clean gloves on hands to prevent transfer of grease to part.

  2. #2
    Join Date
    Aug 2011
    Posts
    623

    Re: Adhesion on overmolded PCB with PA 678

    Hello,
    This is does to post mold shrinkage. Can you try to overmold the parts one or two days after you mold the substrate (1st part)?
    Let us know.
    Suhas

  3. #3
    Join Date
    Dec 2012
    Location
    Serbia
    Posts
    102

    Re: Adhesion on overmolded PCB with PA 678

    I get as material (semi-product) PCB and i (try) to make it waterproof (pucture below).
    Click image for larger version. 

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    Click image for larger version. 

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    This is before and after overmold. As you can see im also limited with preassure, speed and temperature because of wires. If is to high it will damage them.

    One of solution that i found is maybie drying PCB before mold to have better adhesion, but im afraid that after it will be damaged.
    In any case i will try it.

    I hope it will solve this nightmare, but personaly i think chanses are slim.

    Im open for all sugestions.

    Regards,

  4. #4
    Join Date
    Apr 2021
    Posts
    4

    Re: Adhesion on overmolded PCB with PA 678

    Hi

    Have you tried heating the PCB just prior to over moulding instead of drying it. Maybe use a hot air gun to heat the surface then overmould. Just heat to match the mould temperature.

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