Meaning
Mathematical ratio representing the difference between the number of potential chips on a wafer and those that are actually shippable. Analysts use the gross to net yield to identify the cumulative losses from all stages of production including fabrication, testing and packaging. While gross yield accounts for the success of the silicon processing, the net figure subtracts units lost during dicing and encapsulation.
This metric is the final measure of how much salable product was generated from the initial raw material investment.
Loss Calculation
Tracking the disappearance of units occurs at every transition point in the manufacturing line. The journey from a gross to net yield begins with the initial electrical test results and continues through the physical stress of cutting the wafer into individual dies. Some units are damaged during the wire bonding process or fail to meet thermal specifications after being sealed in their housing.
Each of these steps reduces the total number of parts that can be sold to the end customer. These losses are categorized by cause, such as mechanical chipping, contamination during sealing or failures in the final burn-in test. Understanding these specific failure modes is necessary for continuous improvement in the factory.
Manufacturing Efficiency
Optimization of the production flow aims to minimize the gap between the two yield figures. A small difference between gross to net yield indicates a highly refined assembly and packaging process. If the gap is large, it suggests that the packaging technology is not well-matched to the chip design or that the handling procedures are causing physical damage.
Improving this efficiency is often cheaper than improving the base silicon yield because it involves mechanical rather than chemical processes.
Contractual Delivery
Meeting the volume requirements of a supply agreement depends on an accurate prediction of these losses. Sales teams use the historical gross to net yield data to determine how many wafers to order from the foundry to satisfy a specific customer demand. If the assembly losses are higher than expected, the company may fail to meet its delivery commitments even if the foundry performed well.
Maintaining a buffer in the production schedule helps mitigate the risk of these late-stage losses.
