Evaluating the Tripod as an Alternative Cross-Sectioning Method
The electronics industry has been using the epoxy puck to process the vast majority of electronics micro-sections since the 1970s. Not much has changed in that cross-sectioning method, which is now used for precision micro-sections of PCBs, PCBAs, and device packages.
At Foresite, we extensively use a tripod fixture to prepare our cross-sectioned samples for imaging, either with optical or electron microscopy. Here is some insight into our method.
The Traditional Method
Encapsulating samples in a cylindrical “puck,” using either thermal-cure or room-temperature-cure epoxies, has been the standard operating procedure for cross-sectioning electronic samples for years. However, this method can be somewhat limiting in the preparation of specimens to be analyzed where there is a need for a specific angle of attack and/or a requirement to stay parallel to a datum plane. Additional disadvantages or weaknesses in this method also exist.
Tripod: A Usually Advantageous Alternative
Cross-sectioning using a tripod micro-section fixture dates back to the late 1980s, but has primarily been used for silicon wafer analysis. Considering the degree of control needed for wafer and die cross-sectioning, we wanted to bring the advantages of this method to our analysis of SMT and PCB sections. Those advantages include the following:
Easier specimen positioning and repositioning, if desired
Reduction of bulk material (epoxy), resulting in the following:
A faster rate of removal/less processing time
Less grit and polish consumption
Less removed material (less waste and reduced potential to affect the specimen)
Minimal light distortion
Advantages during SEM imaging
Although this manual method limits the size of the specimen and requires dedicated fixtures throughout the analysis, we find that using the tripod fixtures, in most instances, proves beneficial.
Other Cross-Sectioning Considerations
For other cross-sectioning considerations, download “Alternative Methods for Cross-Sectioning of SMT and PCB-Related Architectures” by Manuel “Paco” Solis. He outlines more details on cross-sectioning techniques, including hints and recommendations related to:
Bulk material removal
Sample encapsulation (pre, micro and mini)
Handling of flux residues and conformal coatings
Grinding and lapping
Sample cleaning
SEM imaging