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AUGUST 2019 I SMT007 MAGAZINE 71 ing a proper measurement system was neces- sary for setting up a proper automated-spray- ing process with good process controls since the thickness is a critical parameter of the con- formal coating process. In the early stages of process development, after the machine was selected and installed, a slight anomaly was observed in the conformal coating. As fiberglass coupons had tradition- ally been utilized, and the new steel coupons were beginning to be used, a slight fogginess on the steel coupons was observed. This foggi- ness did not appear on the fiberglass coupons, circuit card assemblies, or on the steel cou- pons that were being hand-sprayed. Fogginess only appeared on the steel coupons being used in the new automated coating machine. Addi- tionally, it appeared that as the pot life aged using the automated machine; there was no fogginess observed on the steel coupons that were sprayed with the older material. After this observation, significant testing was per- formed to attempt to eliminate the fogginess. A series of experiments were performed by adjusting spray-valve distance from the sub- strate, syringe material pressure, atomizing air pressure, thinner to material ratio, valve speed, number of coats, and material flow rate to determine if any of these improved or wors- ened the fogginess on the steel coupon, but none of these parameters had any impact. It was at this point that it was necessary to send samples to a lab for analysis. Five samples, as shown in Table 1, were sent for Fourier- transform infrared spectroscopy (FTIR) analy- sis. The samples sent for analysis included a representative sample of auto-sprayed foggy and clear coupons, steel and fiberglass sub- strates, and material used within and exceed- ing pot life. The concern was that on the foggy coupon (Sample 4) the material may not be properly mixed, or the thinner is not able to escape, or there was some reaction with the new steel coupon. The FTIR analysis was uti- Figure 4: Standard deviation of measurements. Table 1: Samples for FTIR analysis.