A California-based healthcare testing startup, faced a critical quality crisis with their COVID-19 PCR rapid test cassettes during the height of the pandemic. While the test components functioned properly, they exhibited surface-level crack-like appearances that medical customers refused to accept, threatening the loss of an entire manufactured inventory. With no functional issues present, the company needed urgent failure analysis to determine if the components were safe for use and to understand the root cause of the visual defects. ESi was contacted to investigate 28 sample components across multiple mold cavities, with Cavity 1 showing particularly high failure rates.
Our Approach
ESi conducted a comprehensive failure analysis investigation using advanced polymer characterization and microscopy techniques. The team performed systematic evaluation including material identification via Fourier-Transform Infrared (FTIR) spectroscopy, residual stress analysis using polarized light, dimensional analysis of critical features, and detailed optical and scanning electron microscopy of sectioned components.
Investigation revealed that cassettes were injection molded from polystyrene in a 4-cavity mold, with biaxially oriented polystyrene (BOPS) film ultrasonically welded to one surface. ESi analyzed pre-weld and post-weld components from all cavities, comparing cracked and uncracked samples to isolate the failure mechanism. The analysis included cross-sectional examination of the film-substrate interface, stress pattern evaluation, and identification of areas where film adhesion was compromised. Through systematic comparison of welded and unwelded components, ESi traced the visual defects to their source in the manufacturing process.
ESi’s investigation determined that the cassettes were functionally sound with no structural defects. The crack-like appearances resulted from wrinkling in the BOPS film's underlayer due to inconsistent ultrasonic welding, creating optical illusions of cracking without actual structural damage to the polystyrene substrate. The wrinkles formed when the film's biaxial orientation relaxed unevenly during the welding thermal cycle, particularly around the spherical design features where stress concentration was highest. ESi's microscopic analysis confirmed that no true cracks existed in either the film or substrate material, and the structural integrity of the weld joints remained intact throughout all examined samples.
Services Utilized
Expertise Utilized
The Outcome
ESi’s findings enabled our client to confidently ship their manufactured inventory, preventing substantial financial loss and ensuring continued supply of critical COVID-19 testing equipment during a period of urgent need. The analysis provided actionable process improvement recommendations to optimize welding parameters and prevent future quality issues.
