What is Die Strength Testing?

Nordson DAGE bond testers are industry leaders when testing bonds in microelectronics, but did you know that the exact same machine can also be used to test the die itself? Electronics place a reliability factor in all the components working as intended – silicon dies are particularly vulnerable to damage, just as solder bonds are. There are a variety of ways to characterize die such as cantilever bend, spherical bend, three-point bend, and four-point bend. Furthermore, Nordson DAGE bond testers can accommodate a wide range of shapes and sizes of dies for testing beyond the standard.

Standards for Dies & Passive Components

Standard Description
SEMI G86-0303, SEMI G96-1014 Three point bend test of die and cantilever bend of die
IEC 60068-2-77 SMT resistors and capacitors
ASTM C1161 Four point bend
ASTM C1499 Equibiaxial ball on Ring
AEC-Q200 Qualification of Passive Components
ASTM C1239 Standard Practice for Reporting Uniaxial Strength Data for Advanced Ceramics

 

The Challenge

The current trend for thin substrates and large area devices means that dies are more susceptible to fracture from small cracks induced during dicing and thinning. Whether or not a die will fail is dependent on the stress applied and the frequency of any defects present. There are numerous factors that require each individual die to undergo strength testing.

Inorganic semiconductors are delicate, and their strength is largely affected by the presence of surface flaws such as scratches and chips.

  • CTE mismatch or flexure of the board they are mounted onto can expose the die can to high levels of stress.
  • Handling, dicing processes, and back thinning all inflict scratches into a die, so the question is not ‘are there defects on the die’, but ‘what effects do the defects have on die strength?’
  • Flexural testing is perfect for assessing the impact of defects (cracks) and surface treatments on the strength of brittle materials. As silicon dies are brittle, consistent set-up of the testing process is vital to generating repeatable results. A robust and decent set-up for die strength testing needs to be:
  1. Quick and repeatable
  2. Repeatable and accurate micro tool positioning (both X and Y)
  3. Results that are easy to interpret.

It is necessary to be accurate when choosing which test you should perform, and this is typically done based on the thickness of the die. For thicker die, bend testing is recommended, while for thin die, the cantilever test can be used:

Choosing the right test method.

Figure 1: Choosing the right test method.

Bending loads can be caused by thermal expansion.

Figure 2: Bending loads can be caused by thermal expansion.

Three-Point Bending

The standard way of testing silicon die strength is the three-point bend test, which includes pushing the die down with a roller (or indenter) in the center and supported at the sides. The PP50KG cartridge is available for accurately measuring large bend loads during testing of large samples. The three-point bend apparatus can be converted with ease to perform four-point bend by simply replacing the single roller with a dual roller assembly. Unlike three-point bending, where the stress increases to a peak under the center roller, four-point bending produces a constant bending stress between the two upper rollers. Thus, four-point bending is reliable in producing more consistent results, but can only be done on thin, relatively long components.

Nordson DAGE manufactures a range of support anvils to provide a support span for a wide range of die sizes, as the ideal test has a large proportion of the die unsupported. Using the PP500G cartridge, small dies can be tested, which is accurate down to 0.5 g force. The three-point bend set-up meets SEMI G86-0303 and other required international standards.

Support anvils can be customized so that the die can be easily slotted into position against a hard stop to enable rapid, easy positioning every time. When a variety of die sizes needs to be tested, the die can be placed accurately using the nudge function of the bond tester and then independently checked with the image capture camera, to achieve great precision.

Micro three-point bend set-up with self-aligning tool.

Figure 4: Micro three-point bend set-up with self-aligning tool.

Standard and customer options anvils for micro three-point bend.

Figure 5: Standard and customer options anvils for micro three-point bend.

Cantilever Bend

The deflection throughout a three-point bend can cause the die to slip during the test.  When the die is long and thin, this can lead to invalidating the results. Nordson DAGE bond testers can carry out cantilever bend tests for these components. The die is secured into a support and pressure applied to the top is pushed to bend the die. The equipment for the bend test is designed to be compatible with the typical international standards, including SEMI G96-1015. Cantilever bend enables the bending span to be quite short, eradicating the need to go to very large deflections. On Nordson DAGE bond testers, this bending span of small proportion is controlled with precise measures by using the shear height function - consistent bending span is extremely important in generating consistent test results.

A cantilever bend test.

Figure 7: A cantilever bend test.

Spherical Bend

As edge and surface flaws dominate the strength of silicon materials, it is sometimes required to test a die without loading the edge. The solution is to use a ball as the indenter while the die is supported with a ring, thus, ensuring that the edges are outside the loaded area.

Ball-on-ring bend testing.

Figure 8: Ball-on-ring bend testing.

Analysis

A way of understanding the data from testing brittle materials is through the influential Weibull analysis. Paragon™ software supplies a Weibull plot as standard, doing away with the need to carry out post-processing on the results. Additionally, Paragon™ uses the sample dimensions to enable the results to be plotted in terms of stress and strain, rather than simply load and displacement, ensuring that the results can be compared with samples of varying sizes.

Weibull distribtuion analysis.

Figure 9: Weibull distribtuion analysis.

Paragon Materials™ die bend testing screen.

Figure 10: Paragon Materials™ die bend testing screen.

Choose the Right Method for Your Die Testing

No matter what size of your die, Nordson DAGE supports all the relevant test methods for proficient die bend testing.

This information has been sourced, reviewed and adapted from materials provided by Nordson DAGE.

For more information on this source, please visit Nordson DAGE.

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