Seeking to develop a two-part polymer adhesive bonding step in their assembly process, a medical-device manufacturer in the northern United States performed extensive design of experiments (DOE) with multiple variables. The team sought to characterize the process and ensure the process met the appropriate internal, federal and international standards. The parts were sensitive to ambient humidity, so it was important to maintain tight environmental control during the thermal cure step. In addition, the manufacturer needed to use vacuum and heated centrifuges to eliminate bubbles and outgassing in the part.
While the parts seemed to bond well initially, accelerated age testing revealed that in many trials, bonding strength diminished over time — as had appearance and other measures of quality. The testing result indicated that ultra-precise temperature control was necessary to ensure proper finished goods. Outside of that precise process control window, quality was diminished. Lesson learned: Temperature matters.