Nolan’s Notes: Finding Your Sweet Spot
Standard of Excellence: Delivering Excellence—A Daily Goal
Knocking Down the Bone Pile: Tin Whisker Mitigation in Aerospace Applications, Part 3
Pad Cratering Susceptibility Testing with Acoustic Emission
July 22, 2015 | B.S. Wong and J. Silk, Keysight Technologies, and R. Nordstrom, Ph.D., Emerson Process ManagementEstimated reading time: 16 minutes
Figure 7 shows that Laminate F is a frequent AE emitter as evidenced by the significant number of AE events with amplitude greater than 40 dB that occurred when both the applied load at 30lbs and 50lbs compared to other five laminates. Figure 8 shows that Laminate F released significantly more energy than other laminates when both the applied load at 30lbs and 50lbs. Both the number of AE events at given applied load and the cumulative energy of AE events at given applied load indicates that Laminate F is prone to pad cratering.
Our empirical experience with laminates is that Laminate F is inferior and that Laminate A, our control laminate that is dicy-cured, is superior. Laminate F proved to be a frequent AE emitter, confirming our experience. The expected superiority of Laminate A is not evident; this may be because of degradation due to incompatibility of this laminate with the multiple high temperature reflows. The degradation with additional reflow cycles seen in the other test methods reported in our earlier paper [8] was not found, although with this test method we compared only 5 and 7 reflows.
Verification of pad cratering was done with cross-sections. To enhance the visibility of the pad craters, two methods were tried: powder filling and polarized light. Polarized light produced much more visible pad craters. The vast majority of the pad crater failures were, not surprisingly, at the corners of the largest BGA. Fig. 9 shows examples of pad cratering.
As indicated in Figure 5, not all AE events are associated with pad cratering because some AE events are located outside of the package. Figure 10 shows two examples of laminate cracks indicated by AE events, but not associated with pad cratering. The cross-sectioning results confirm this finding.
Table 2 compares results of various test methods for evaluating pad cratering. Note that the results of six different laminates’ resistance to pad cratering using the ball pull, ball shear, and hot pin pull tests (please refer to our earlier paper [8]). This ranking of laminate materials shows quite a bit of inconsistency of results among the methods. No conclusion can be drawn at this time as to which test method is better able to distinguish the laminate materials’ resistance to pad cratering.
Figure 6: (a) The applied load at first locatable AE event with amplitude greater than 40dB, (b) Average applied load when first four AE events with amplitude greater than 40dB.
Figure 7: (a) Number of AE events with amplitude greater than 40dB when the applied load is 30 lbs, (b) Number of AE events with amplitude greater than 40dB when the applied load is 50lbs.
Figure 8: (a) natural log of cumulative energy of all AE events with amplitude greater than 40 dB when the applied load is less than 30lbs, (b) natural log of cumulative energy of all AE events with amplitude greater than 40dB when the applied load is less than 50lbs.
Page 4 of 5
Share on:
Suggested Items
KYZEN to Highlight Understencil and PCB Cleaners at SMTA Querétaro Expo and Tech Forum
07/09/2025 | KYZEN'KYZEN, the global leader in innovative environmentally responsible cleaning chemistries, will exhibit at the SMTA Querétaro Expo & Tech Forum, scheduled to take place Thursday, July 24, at Centro de Congresos y Teatro Metropolitano de Querétaro.
Driving Innovation: Direct Imaging vs. Conventional Exposure
07/01/2025 | Simon Khesin -- Column: Driving InnovationMy first camera used Kodak film. I even experimented with developing photos in the bathroom, though I usually dropped the film off at a Kodak center and received the prints two weeks later, only to discover that some images were out of focus or poorly framed. Today, every smartphone contains a high-quality camera capable of producing stunning images instantly.
Hands-On Demos Now Available for Apollo Seiko’s EF and AF Selective Soldering Lines
06/30/2025 | Apollo SeikoApollo Seiko, a leading innovator in soldering technology, is excited to spotlight its expanded lineup of EF and AF Series Selective Soldering Systems, now available for live demonstrations in its newly dedicated demo room.
Indium Corporation Expert to Present on Automotive and Industrial Solder Bonding Solutions at Global Electronics Association Workshop
06/26/2025 | IndiumIndium Corporation Principal Engineer, Advanced Materials, Andy Mackie, Ph.D., MSc, will deliver a technical presentation on innovative solder bonding solutions for automotive and industrial applications at the Global Electronics A
Fresh PCB Concepts: Assembly Challenges with Micro Components and Standard Solder Mask Practices
06/26/2025 | Team NCAB -- Column: Fresh PCB ConceptsMicro components have redefined what is possible in PCB design. With package sizes like 01005 and 0201 becoming more common in high-density layouts, designers are now expected to pack more performance into smaller spaces than ever before. While these advancements support miniaturization and functionality, they introduce new assembly challenges, particularly with traditional solder mask and legend application processes.