The stud-pull test measures the bond strength of dies and other flat components to the substrate. This is a complementary technique to the more common die shear test, with both methods being used to get a full understanding of the die-substrate bond strength. Stud-pull is carried out in pure tension, so the stresses on the bond are less complex, so the bond performance is easier to model. An important industry trend is for dies to become wider and thinner, which makes them more difficult to test using shear, so pull testing is becoming an essential technique. Shear tests can cause bending of the die or substrate during the test, so the stress state becomes a combination of shear and tension. This bending gets worst as the die area increases relative to the thickness of the die. Stud-pull testing eliminates this issue.
Nordson DAGE bond testers support two methods of pull testing; a vertical pull test, that allows access to the smallest and most difficult-to-reach components, and a horizontal pull test that can test the largest components, with a full load of 200 kg force.
The challenges of a successful stud-pull test are:
- Achieving a perfectly perpendicular pull off the substrate, thus minimizing peel forces
- Securing the substrate during the test so that the die can be tested without breaking the substrate first
- Using a load cell that can measure small pull tests accurately, yet has sufficient pulling force to test large components
Schematic representation of shear (left) and pull (right) tests on dies connected to substrates. Pull testing avoids any bending of the die, which can happen during shear tests.
The Vertical Pull Method
For the vertical stud-pull method, Nordson DAGE pull cartridges are utilized. A wide range of cartridges that can be interchanged at high-speeds are available, from the P25G, with a 25g capacity, up to the P100KG. Securing the package or support plate using the standard work-holder, the stud is glued to the die surface using a high-strength adhesive such as cyanoacrylate. The die is then placed under the cartridge utilizing the high-precision xy stage that guarantees the stud is pulled vertically during the test.
The Horizontal Pull Method
The horizontal pull method uses a cup that smartly fits around the edge of the die when the load is applied to react to the loads of high-force pull testing. The die being tested is usually much larger for these tests, with a standard stud of 8x8 mm bond area available.
A wide range of standard cup shapes and sizes can be found, with custom cups also available. So that the substrate does not twist or buckle during testing, the cup supports the substrate around all the die edges. This process uses a Nordson DAGE shear cartridge (such as S200KG) and a fixture. An aluminum plate can be affixed to the rear of the substrate when the substrate is especially flexible.
This information has been sourced, reviewed and adapted from materials provided by Nordson DAGE.
For more information on this source, please visit Nordson DAGE.