For devices that must survive extreme environments (automotive under-hood, aerospace, medical implants), the SPAD alone cannot remain crack free without reinforcement. Capillary underfill (CU) is the gold standard.
Underfill material (silica-filled epoxy) flows beneath the component and encapsulates every SPAD. It distributes thermal stress across the entire array rather than individual pads. When a customer demands "SPAD next crack free" in an ISO 26262 (automotive safety) context, they are implicitly requiring underfill. Without it, drop shock reliability falls from >1000 cycles to <100 cycles. spad next crack free
The most common culprit. The PCB laminate (typically FR-4 with a CTE of 14-17 ppm/°C in-plane and 50-70 ppm/°C through-thickness) expands and contracts at a different rate than the ceramic or silicon component (CTE of 2.6-6 ppm/°C). Every power cycle induces shear stress on the SPAD. After thousands of cycles, fatigue cracks nucleate at the pad corner. It distributes thermal stress across the entire array
SPADs are semiconductor devices that operate in Geiger mode, meaning they can detect single photons due to their high sensitivity. When a photon hits the SPAD, it triggers an avalanche of electrons, which can be easily detected. This capability makes SPADs extremely useful for applications requiring high sensitivity and timing resolution. The most common culprit
1500G, 0.5ms duration, 30 drops. A crack-free assembly shows no electrical discontinuity >1 microsecond.
If you use a cracked tool to analyze a SPAD incident and present that analysis to the Rail Accident Investigation Branch (RAIB) or a safety review board, what happens when they ask for the software license and version validation? You have zero credibility. In safety-critical industries, the chain of trust matters. If the tool isn't legitimate, the output isn't admissible. You could lose your job or your consultancy contract.
A 45° metallurgical cross-section through the BGA corner SPADs, examined under a Scanning Electron Microscope at 2000x magnification. Any crack >1µm is a failure. "Crack free" means zero observable intermetallic separation.