PCBs, Electronics & Semiconductors

Printed Circuit Board Strain Testing - Components are attached to printed circuit boards, PCBs, by solder connections of various kinds. During assembly, installation, shipping, and/or use the PCBs may bend and strain the solder joints leading to immediate failure, or an unreliable product down the road. We have performed strain measurements to determine the risk of failure to mount electronic components on printed circuit boards.

Strain gage rosettes on PCB for testing solder ball joint strains as per IPC-WP-011

 The standard we often test requires measurement of both the principal strain and the time rate of change of strain, Strain Rate, characterized for various parts of the manufacture and assembly process. The risk of weakening, or failing, a solder joint depends not only on the strain levels, but on the rate of change of strain level, as the elasticity of the solder joint is, apparently, frequency dependent. One particular test procedure we use follows standard IPC/JEDEC-9704A, 2012 – February, titled Printed Circuit Assembly Strain Gage Test Guideline. The allowable strain levels, for instance, are provided in IPC-WP-011, titled Guidance for Strain Gage Limits for Printed Circuit Assemblies(Rate Limited), but our client may have their own allowable limits as well that they have derived through testing of their product.

Based on IPC/JEDEC-9704A, the highest priority components to measure are the components that utilize ball grid array (BGA) connections. Strain signals were measured from each of the three strain signals coming from each of the four rosettes mounted near the four corners of the graphics processor chip. The raw strain signals were digitally processed in real-time to compute the two principal strain signals and the strain rates.

Strain and Strain Rate, Time Domain Signals

Strain vs. Strain Rate for IPC-WP-001

Strain Measurement on PC-board Investigating Solder Ball Connection Strains in Various Loading Configurations

We provide strain gage services to compliment our analysis in many areas of the electronics industry. This includes R&D of the many high resolution tools and processes of the semiconductor industry, to the product level of the electronics industries.

In the semiconductor industry, at the R&D phase, we have used strain gages to help develop the cutting edge high-tech semiconductor equipment that is part of the effort to produce electrical components of ever diminishing size. As vibration consultants in the semiconductor industry for over 3 decades we have been involved in many unique projects where strain is of interest. In validating and trouble shooting a design we may use strain gage testing, in conjunction with our Vibration Testing Techniques, to deduce the force transmission paths, or to estimate vibration isolation effectiveness. In this area the strain gages have been used to determine the load acting on the vacuum chamber of a scanning electron microscope from a novel turbo-pump isolation system. Micro-vibration limits how small lines can be etched, or how well a tool can resolve an image. Design for mitigation of vibration is a major consideration.

For example, we have used strain gages to separate out the moment and shear forces acting at the bearing frequencies of the high speed vacuum turbo pump to evaluate various novel vibration isolation designs. Our approach allowed us to efficiently quantify the residual transmitted forces. Knowing the force geometry, phase, and spectral content, our team was able to optimize the isolation mount. We could also provide customers with valid estimates of resulting pump induced chamber vibration without testing the pump on the large variety of vacuum chambers sizes. These turbo pumps are used in scanning electron microscopes and other process and inspection tools.

Semiconductor cleanrooms contain some of the most sophisticated technologies, we have designed tests for many of these tools

Scanning Electron Microscope (SEM) Image, showing image disturbance

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Call Reuben Hale, P.E. at 510-507-1300
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