January_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y 2 0 2 0 1 9 points were apparent, this would sig- nal a manufacturing flaw. Conversely, the presence of the initial solder points with copper wire breakage occurring elsewhere would confirm post-man- ufacture handling as the most likely culprit. Due to the size, encasing materi- als, and internal location of these fea- tures, visual inspection, component disassembly, and NDT were ill-suited to provide a solution. Therefore, me- chanical serial sectioning with Sandia’s Robo-Met.3D was used. Mechanical se- rial sectioning was additionally help- ful because the exact location of the wire breakage was unknown, and it was hidden from view by the solder cap, as shown in Fig. 2(a). Use of the Robo-Met.3D allowed for precise depth control during seri- al sectioning, which in turn facilitated locating the wire connection on such a small part. It would be exceptionally challenging and impractical to locate the wire connection using manual pol- ishing due to the accuracy required, which was repeatably obtained at two microns per slice using Robo-Met.3D. Figure 2(c) presents progressive slices from the micro-inductor initially into the part (slice 98), at the start of the wire connection (slice 220), in the mid- dle (slice 235), and at its end (slice 260). Using this data, the wire connection was located between 235 and 315 mi- crometers. It was determined that the lead wire was at one time correctly lo- cated and connected, and the wire de- tachment was most likely the result of post-manufacture handling. This find- ing drastically reduced performance concerns from the manufacturing of a batch of parts to a finite number of downstream handling events. Case study #2 – Cracks in glass-to- metal seals: Glass-to-metal seals for connectors often exist in the range of 5 x 5 x 5mm 3 and are useful for their her- miticity, durability, and electrical isola- tion properties. These seals generally consist of an electrically conductive pin encased in a glass seal that is fully en- closed by a housing material, typically a structural metal. Manufacture is com- pleted by filling the hole in the housing material with molten glass and pushing the pin through the glass. The glass-to- metal seal is then created as the glass cools and hardens around the pin. Problems during manufacturing or handling can lead to cracks within the glass. Inspection of these seals is challenging because cracks are often invisible after assembly and are difficult to identify using NDT. Here, mechanical serial sectioning was used to determine (1) the extent of cracking, (2) the char- acter of the cracks and (3) the influence of the inspection direction on crack measurements. Seals were inspect- ed in two primary directions, trans- verse and longitudinal, with respect to the pin, as shown in Fig. 3. Serial sectioning was completed through 150- 200 slices across several seals with an approximate material removal rate of 15 microns per slice. This study revealed multiple find- ings. First, in the representative exam- ples shown, cracks were observed in both seals, but the extent of cracking was more severe in the longitudinal mounts compared to the transverse. In the longitudinal mounts, Fig. 3(a), cracks running the full length and radi- us of the seal were observed immedi- ately upon entering the glass from the surrounding housing material. These cracks persisted through the seal until reaching the pin. In contrast, the trans- verse mount showed cracks with a sim- ilar arrangement, but only persisting through approximately 45% of the seal length and radius. Second, in both lon- gitudinal and transverse orientations, Fig. 3 — Analysis of glass-to-metal seals in (a) longitudinal and (b) transverse directions. Cracks are shown at three different depths for each representative experiment. Darkfield optical imaging was performed with a Zeiss Axio Observer.Z1 inverted microscope to illustrate surface and subsurface cracks.