Zone shear

In this technique a chisel-like tool is used to clear several rows of solder balls at once. The principle of the method is that the action of the shear tool on multiple balls initiates a peeling action, supposedly then probing the bond adhesion on the device. As high forces are involved, some modification of the 4000 machine is required: a high power XY stage and a 100kg load cell.

Normally this technique is carried out at relatively low speeds of 5mm/s.

Advantages and disadvantages

The two advantages of this test are that there is minimal sample preparation and many bonds can be tested simultaneously. However, given that it is carried out at conventional shear speeds, and initiation of peeling action may not be consistent, there is no guarantee that the integrity of the bonds themselves are being tested.

It is important to understand the limitations of zone shear:

• Despite the fact that balls do not need to be cleared from the device, it is very important that the device is aligned correctly in the work holder. Otherwise, the shear tool can plough into the substrate, damaging it, and probably compromising the test. Sample alignment could easily be a cause for poor reproducibility in zone shear.
• Data collection is relatively rapid, but it is also subjective and prone to operator error. The percentage remaining area of solder on each sheared ball must be assessed (usually to the nearest 10%). Prior to the test, the engineer must decide the criteria for failure, both in terms of percentage remaining solder and the number of bonds showing at least that level of solder.
• The fundamental operation of the test with the load on the bonds varying from ball to ball is not conducive to test reliability and reproducibility.

In order to help you choose the type of bond test most appropriate to your purposes and application we have prepared the following table as a quick reference comparing the main features of each test type.

Which bond test?