Standard Test Methods for Measuring Pull Strength of Microelectronic Wire Bonds

Theory:

ASTM F549 is a procedure for testing the pull-off strength of bonds made on a Printed Circuit Board (PCB). These bonds are usually made of a thin wire. Failure of an electronic interconnection is the #1 failure mode for most PCB and electronic devices such as computers or smartphones. 

 

Since almost all electronic circuitry is bonded by small wire, this test can be extrapolated beyond soldered wire connections. Plugs and board components such as the processors, resistors, and capacitors, can all be pull tested under this specification. 

 

Based on the scope of this specification, these methods can be used to develop in-line tests. There is also a series of accompanying non-destructive testing for PCB circuits that is covered in ASTM F548. 

 

Geometry:

This test is optimized for wire bonds in the range of 20-80 microns. The specification cites a basic L hook that can be used to perform the test, however it is often times difficult to get the appropriate hooking on the bond.  

Solution:

Universal Grip offers a miniature pinching device which is anchored with a chain. The chain gives the technician the freedom to choose which component or bond is to be pulled. It also self aligns during the test which can be seen in the video. 

Analysis:

There are a few specific calculations for ASTM F549, however these are mostly used only in R&D settings. The pull strength is a function of the load, as well as several of these other measured variables which can be seen in the SEM picture to the left. Most quality programs will simply measure the pull strength as the maximum load experienced during the test which is 2.5 newtons in the video.