While engineering development uses the strengths of an organization, in many instances, factors beyond the core strengths of the engineering team play a critical role in the success or failure of a product.
In the new design of an analytical instrument, the mechanical engineers were looking for a convenient way to maintain a sealed environment but allow the customer to open an optical compartment when necessary. In prior designs, a metal cover with gasketing and screws had been used. The customer base found this objectionable because of the necessary tools and the quality engineer was afraid that if screws were used, the customers would not replace the lid properly and compromise the instrument.
The design solution was to make a rubber plug to inset into the whole. But in solving one problem, another arose. In the prototype instruments, a film developed on critical optical surfaces and the optical throughput of the instrument dropped.
Fourier Transform infrared spectroscopy was used to examine both the prototype rubber plugs as well as areas from the clouded mirrors.
The plugs were found to be a silicone rubber and during the examination the analyst noted a “greasy” feel to the plugs. The deposits on the mirrors were siloxanes (low molecular weight silicones). Discussions with the vendor revealed that the plugs were not cured properly. The cause of the deposits and the greasy feel were low molecular weight silicones. A specification was set for production cure time and the problem was solved.
A new PCB manufacturer is chosen and asked to submit qualification samples of a legacy PCB product. Continuity testing on the as-manufactured raw PCB revealed open circuits present.
Coupons are excised at three different PCB and via hole size regions for both vertical and horizontal cross section preparation. Vertical cross sections are used for via and PTH plating thickness analysis, inner and outer-layer interconnect characterization, laminate characterization, etc. Horizontal cross sections are used for registration characterization, etc.
Optical and chemical techniques can provide a wealth of information in this case. Careful mechanical section sample preparation is key. Followed by Optical Microscopy (OM) on polished, and after chemical etching as well as the chemically etching itself can bring to light areas of failures . Cross section sample preparation is not trivial and in many cases can disguise anomalies if not performed correctly. These anomalies may prove to be catastrophic Cross section feeds and speeds, proper grinding techniques, all can impact the quality of the final polished specimen. Chemical etching can also disguise anomalies as well if not performed correctly.
Examination of the vertical cross sections revealed anomalies (subtle separations) present at the via barrel to inner-layer interconnect interfaces specifically at the electroless copper to inner-layer copper foil interface. The cause was incomplete etch back/de-smearing procedures after hole drilling. The subtle separations were also observed to cover most of the circumference of the via barrel/inner-layer interconnect interface during horizontal cross section analysis.