Reject Rate
The proportion of manufactured components that fail to meet specification during environmental and electrical stress testing defines the effectiveness of a quality assurance program. This metric, known as screening fallout, provides crucial information about the maturity and stability of the fabrication process.
Stress Protocol
Production batches are subjected to accelerated lifetime trials, including thermal cycling and high-voltage burn-in, to trigger early life failures before the parts are shipped. These demanding trials are designed to expose latent defects such as weak wire bonds or sub-optimal solder joints. The quantity of components that fail during this stage is carefully tracked.
Process Improvement
Analyzing the causes of screening fallout helps to pinpoint specific vulnerabilities in the assembly line. For instance, a sudden rise in fallout related to die-attach voiding suggests a malfunction in the adhesive dispensing equipment. By correlating the failure modes with the production log, corrective actions are applied to prevent future yield losses.
Cost Impact
A high rate of screening fallout increases the manufacturing cost per unit because additional materials and labor are required to replace the failed parts. However, this cost is far lower than the financial penalties and damage to reputation associated with a field failure in a safety-critical application. Balancing the severity of the test screen with the acceptable reject rate represents a major decision in production planning for high-reliability industries.
