The corrosion was real. The root cause was invisible to every instrument they had.
A large international semiconductor manufacturer used APMON in a Six Sigma program to identify the non-airborne particle sources causing device failure — and found that more than 80 % of the contamination was coming from their own people.
The problem had been present for years: unexplained corrosion in packaged semiconductor devices, appearing in field returns without a traceable assembly cause. The quality team had conducted multiple investigations. The cleanroom held its ISO class. The particle counter at the standard sampling location showed nothing unusual. Die bonding yields were within specification. Wire bonding passed inspection. And devices still corroded in the field. The root cause investigation had reached the limit of what airborne particle monitoring could reveal.
The investigation shifted when the scope of measurement shifted. A particle counter measures particles suspended in the air — particles up to approximately 10 μm that move with the airflow and are sampled at a fixed point. It does not measure non-airborne particles: the macro-particles and fibres greater than 15 μm that are too large and too heavy to remain suspended, that fall from personnel and surfaces directly onto the product. These were the particles causing corrosion. Fibres from garments, skin-cell fragments, particles from tools and fixtures — depositing onto the die surface and lead frame during bonding, during transfer, during handling. APMON was deployed to measure what the particle counter had been missing.
The APMON data revealed the contamination landscape immediately. Deposition events correlated directly with personnel activity: specific entry sequences, garment failures, ungloved handling, inadequate cleaning intervals. The Six Sigma analysis of the event log identified that more than 80 % of the macro-particle deposition at critical locations originated from personnel — from the way they dressed, the way they moved, and the way they interacted with the assembly environment. None of this was visible in the airborne particle count. The program then addressed each source in sequence, measuring the impact of each intervention on the deposition rate at the die bonding location before moving to the next. The corrosion rate in field returns declined with each cycle of improvement.
What the program enabled
Root cause identification — APMON distinguished non-airborne from airborne contamination for the first time in the facility, revealing fibres and macro-particles as the primary failure mechanism.
Source attribution — 80 %+ of contamination traced to personnel through APMON event log analysis correlated with shift records, entry logs, and activity documentation.
Step-by-step PDR reduction — each intervention (gowning improvement, entry barriers, cleaning program upgrade, behavioral training) measured and validated before the next step was taken.
Corrosion reduction in field returns — the improvement in operational contamination control, driven by APMON data, translated directly into a reduction in device corrosion rates in the field.
The particle counter showed a compliant cleanroom. APMON showed what was actually falling on the product. They were measuring different things. Only one of them was measuring the right thing.
THE SIX SIGMA FINDING
The ISO 14644-17 calculation defined the maximum allowable particle deposition rate from the product risk: for a device where 2 particles ≥25 μm on a 10 cm² exposed area during a 30-minute process step was the acceptable limit, the PDR limit was 1,300 particles per dm² per hour. APMON measured the actual PDR at the bonding location during operations. The data drove the Six Sigma program: identify the gap, identify the sources, close the gap one intervention at a time. More than 80 % of the contamination was attributable to personnel. Operational improvements — gowning, entry protocol, cleaning program, discipline — were the solution. No new equipment was required.
