It can be challenging to section electronic components for quality control or failure analysis because care must be taken to make sure that the true structure is revealed, free from preparation-inducted artifacts.
Historically, sectioning processes that caused large amounts of damage to the sample were used, but these could induce artifacts that were easy to misinterpret as manufacturing defects or service failures. In order to avoid this, sectioning needed to take place well away from the region of interest (ROI), and long grinding and polishing stages were needed to recover any damage induced.
The four most common methods of sectioning have historically been router, punch, precision saw and bandsaw. Each has its own advantages and disadvantages. Press and punch are quick, but are limited by the size of the coupon and can cause significant deformation strain on multi-layer boards.
Bandsaws and routers can be set up to handle various part sizes, but can cause heat, as well as causing shear grain on multi-layer boards and acting aggressively towards populated boards. Precision cutting reduces damage significantly but can be limited by board size and, compared to the other methods discussed, historically required slower sectioning of the parts.
Advances in precision saws mean that larger populated or unpopulated boards can be sectioned quickly. Higher torque motors, increased cutting chamber capacity and X, Y and Z axis movement have allowed for greater flexibility in handling samples. The IsoMet High Speed Pro combines automated three-axis movement, a large open working area, a 2-kW motor, laser alignment for visual confirmation of cut and stored methodology. (Figure 1)
Figure 1: Stored methodology can be utilized to ensure cutting in the same ROI if routine work is to be done. Image Credit: Buehler
In order to determine the damage induced from different sectioning methods, cross sections of a 12-layer MIL-SPEC unpopulated board were made. To make sure that superior edge retention was retained during preparation, each coupon was cast in EpoKwick FC (Figure 2).
Figure 2: EpoKwick FC epoxy provides excellent edge retention, low shrinkage and low viscosity. This ensured that there was no board delamination due to sample preparation during the grinding and polishing steps. Image Credit: Buehler
The standard SumMet method for General Electronic Components was used to prepare the samples. The samples were ground and polished perpendicular to the sectioned edge. This meant that the surface left from each of the sectioning methods, and the sub-surface damage induced, could be easily examined.
The samples were photographed and measurements were made to highlight the damage induced by removal. (Figure 3 – Figure 6).
Figure 3: Damage from bandsaw sectioning. Image Credit: Buehler
* Note board cracking perpendicular to layer, delaminating extending ~1500 microns (1.5 mm) from the edge of the cut. Glass fiber chipping noted at 2500 microns (2.5 mm) from the leading edge.
Figure 4: Damage from punch and die sectioning. Image Credit: Buehler
* Note board delaminating within the last 4 layers, distortion of copper layers extending ~1200 microns (1.2 mm) from the edge of the cut. Glass fiber chipping noted at 1600 microns (1.6 mm) from the leading edge.
Figure 5: Damage from router sectioning. Image Credit: Buehler
* Note distortion of copper layers and slight delamination of last two layers with glass bundle chipping extending ~400 microns (0.4 mm) from the edge of the cut.
Figure 6: Damage from IsoMet High Speed Pro sectioning with IsoMet 15HC blade. Image Credit: Buehler
* Note copper and board layers are parallel with little damage to the glass bundles. Damage extending ~20 microns (0.02 mm) from the edge of the cut.
Sectioning methods can induce damage into board material and subsequently require grinding and polishing steps to remove the damage. Damage can be upwards of 2.5 mm, depending on the choice of equipment for removal, and require operators to “grind and find” to make sure unaltered material is revealed. Removal in this way can cause samples to become uneven, or, if sampled too closely, to go past ROI. Using a precision saw, for example the IsoMet High Speed Pro, can ensure that close proximity to the ROI is achieved, without inducing damage.
Produced from materials originally authored by Annie Radville and Todd Danielczyk from Buehler.
This information has been sourced, reviewed and adapted from materials provided by Buehler.
For more information on this source, please visit Buehler.