Wire bonding reliability is certainly critical in PCB microelectronics/wire bonding manufacturing. Wire bond integrity is also related to the reliability of a successful and accurate wire bond. In this particular case, there is actual testing to assure the integrity of wire bonding. It’s called wire bonding pull testing.
Pull testing performs several methodologies to test for several possible failures. Normally, the type of wire used is one to two mil gold wire that is pulled, Fig. 1. The major failures observed during the bond pull test are ball lift, wedge life, mid span break, and ball neck.
Before we go any further here on wire bond integrity, it might be a good idea of revisit wire bond reliability. To get more detail on wire bonding, check out our blog.
In the meantime, here are some tips and hints about wire bond integrity.
- A ball lift failure shows that the ball to bond pad is too weak
- Multiple factors can cause ball lift failure. Poor parameters setting on the wire bonding is one factor. Another factor is contaminated PCB surface finish.
- Wedge bond lift is a separation of the wedge bond from ball bond.
- Wedge bond lift is an indication of improper process optimization. Possible causes include hard metallization or too much gold or silver is used.
- Ball neck failure means the neck of the wire has fractured. The neck is the portion where the wire meets the ball bond neck.
Highly qualified process engineers and experienced technicians need to set wire bonding parameters very carefully prior to performing wire bonding pull testing. Technicians also need to assure that correct tools, fixtures, and jigs are all properly calibrated to the forces that are used. Further, those tools and forces must comply with the requirements of the wire gauge, bond material, substrate materials and PCB surface finish.