Wirebonding
Wirebonding is currently the most widely used chip assembly technique for bare dies.
Wire-bonded chip in the hollow of an injection-molded part
First the die is attached to the substrate with an adhesive, and subsequently its contact pads are connected to the feed lines with a very fine wire of Au or Al with a diameter of from 25 - 70 micron. For protection and stabilization, the chip and wires are then encapsulated (glob top).
The advantages of this method are the separation of the attachment means and the electrical contacting, as well as the high level of reliability in the face of thermomechanical stresses caused by the "flexibility" of the wires.
Wedge - wedge wire bonder from Hesse & Knipps
The disadvantages are the large space requirement outside the chip, the serial bond process and the need of an additional glob top process.
For wire bonding on MIDs, the plastic part and the metallization must form a stable, sufficiently stiff foundation, which can be achieved by an appropriate design and a metal layer sequence.
Metal surfaces with a low degree of roughness are required for secure wire bonding. They can be created with the 2K process and also through a modified LPKF LDS® process.
The Al Wedge-Wedge process is preferred on MIDs as the fusing with ultrasound occurs at room temperature while temperatures of over 100ºC are required for Au wires in the thermo compression process.
Encapsulation can be provided to protect the wires. The encapsulation process is made facilitated considerably by realizable cavities in the injection molding body. The time consuming dispensing of Glob-Top is not necessary.