This extensive how-to consists of 13 paragraphs and 7 pages. Please use the navigation on the right.
This manual is a guide advising what to consider and how to best setup a Cold Bump Pull (CBP) test. It generally refers to solder ball testing but the principles apply equally to most bump testing. Hence, some say Cold Ball Pull testing.
To grip a ball we have to reform it to the shape something like a mushroom. This is done with special tweezer jaws that have cavities that reform the ball when they close.
You might think reforming is bad but think about a shear test. In a shear test the reforming at a typical test force is often more and a lot of it over the bond.
If we get a higher test force by “over gripping” the ball so that the reforming cuts over the bond this is better than a lower force with a ductile or extrusion where the bond was still not tested but at a lower force.
Ideally the “stem” of the mushroom shape is the larger or the same diameter as the bond but if over gripping tests the bond at a higher force, it is a better test.
We might still get a ductile or extrusion when we over grip, but the bond has been tested to the highest force possible.
Not all balls can be effectively gripped by the CBP test method. The ball height to diameter affects what can be tested. The ratio of what can be tested is roughly defined by diameter / height < 2,2.