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NOVEMBER 2017          TAP TIMES          4

                                                                process tool, bond tools experience wear.
                   Wire bonding (from 3)

                                                                Bond tools wear differently
        position, with a fixed orientation, perpen-             In development work, this wear can be
        dicular to the bonding tool.                            extensive and occur rapidly.

                                                                Depending on the type of wire used, bond
        Secure bonding area                                     tools wear differently. When bonding with
        The part must be held so that the area be-              gold wire, material on the end of bond
        ing bonded is secure and free from move-                tools may wear off.
        ment in the X, Y, and Z planes.
                                                                Aluminum wire bond tools can experi-
        Any movement in the part during bonding                 ence wear and can accumulate aluminum
        will absorb energy, which may cause pro-                residue from the bonding process. Ribbon
        cess variation or an inability to bond the              bonding tools tend to chip.
        parts.  For gold bonding the fixture must
        also be able to withstand temperatures                  In an established process, for a specific
        over 100˚C.                                             part, it is not uncommon for a process or

                                                                manufacturing engineer to perform a tool
        It is vital that the fixture hold the part              wear study to determine the tool life and
        securely, not add any unintended stress to              the effect it has on the process stability.
        the part and not interfere with bond head
        movement.                                               Through statistical process control (SPC)

                                                                a techniques upper and lower specification
        Sometimes the part may have a unique                    limits can be established for the wire bond
        package design such that the die is ther-               process.
        mally insulated. This presents further chal-
        lenges when designing a fixture for gold
        bonding as the bond surface must reach                  Wire bond strength
        the required bonding temperature.                       As the bond tool wears, the wire bond

                                                                strength can drift closer to the specifica-
        If wire bond fixtures are intended for me-              tion limit.
        dium to high volume manufacturing over
        the life of the product, then they must be              Once the relationship between tool wear
        built to tighter tolerance and hardened for             and performance is understood, an au-
        long term wear resistance.                              tomatic wire bonder can be set to trigger
                                                                limits for a tool change.
        This hardening will reduce the process
        variation that is introduced over time.                 In a development environment the tool
        Thoughtful design of wire bond fixturing is             wear and buildup is often accelerated due
        time consuming, but it is a very important              to over bonding. It is critical that the bond
        first step.                                             tool be checked before each operation
                                                                change during development.

        Bond Tools                                              All of the peripheral tool components in
        Bond tools are often the most forgotten                                                      See page 6
        process component input.  Like any other
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