Newsletter: The Science of Bond Testing

28 December 2018

The Science of Bond Testing

We at XYZTEC look back at a great 2018 with many new innovations in bond testing and once again record breaking turnover, reaffirming our position as market leader worldwide. In the coming newsletters we will highlight some of the new key features of the Condor Sigma product line. This last newsletter of the year focuses on the science of bond testing in general.

The Science of Bond Testing is derived from decades of experience designing bond tests for the widest range of applications. It elevates bond testing to a science that takes you through the process of designing the optimum bond test for any process.

The Science of Bond Testing analyses the roots of bond testing and teaches what is required to design and perform the optimum bond test. When considering the optimum bond test there are a nearly infinite number of decisions to be made; these can be simplified into 4 parameters:

• Test type
  
  • which type of test, pull or shear?
• Test speed
  
  • what test speed?
• Tool design
  
  • what is the best tool shape?
• Tool alignment
  
  • where to apply the test load?

Find the Failure Modes of Interest

The test load must be applied to some part of the sample and transferred through the sample to the bond. If this part of the sample is the only option and is weaker than the bond itself, then it will fail. The bond will not be tested and the strength/quality will not be known. Ideally the bond test should produce some type of bond failure. This type of bond failure is known as the "Failure Mode of Interest".

A bond test is designed to produce the most Failure Modes of Interest by applying the test load most like the true load (if known) and with the highest force possible.

The Science of Bond Testing - how to design a bond test by getting the most failure modes of interest (click on the image to zoom in)

You are testing with a load most like the true load (if it is known) and testing the bond at the highest force possible. This will give the earliest possible indication of a weakening in bond quality by a change in force and/or failure mode.

Example: Gold Ball Shear

In the case of Gold Ball Shear testing, the target failure mode is often Gold shear, because it indicates a reasonably good bond. But to know the bond strength the test should produce a failure in the IMC, a pad lift or pad crater. It should be noted that by changing the failure mode from Gold shear to a bond failure there will be a coresponding increase in the test force.

There are many different opinions on what the shear height should be, like for example 10% of ball height or a specific dimension. These may or may not be derived from an appropriate understanding but neither are the fundamental answer and both are capable of promoting a false truth. The best shear height is the one that produces the most Failure Modes of Interest. Similarly Gold ball shear is almost always tested with a Chisle Tool but a Cavity Tool will produce more Failure Modes of Interest and higher test forces.

The Science of Bond Testing states: Choose the test that gives the most Failure Modes of Interest using a test type most similar to the true loading condition (if it is known) and if you cannot get a Failure Mode of Interest, test the bond with the test settings that produce the highest load (force) on the bond.

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Aiming to improve understanding of bond testing in the industry, XYZTEC organizes seminars to present and disseminate knowledge in a straightforward format. Click here to find out more about bond testing seminars.

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