I've encountered 4 failed cases with HMC637LP5E in recent NPI. With all biasing and sequencing and input/output impedance matching confirmed to be fine. Only two things to look at are;
1. Effects of solder void on thermal dissipation on the exposed ground paddle. Is 30% void spec sufficient for good thermal dissipation?
2. Higher failure rate on HMC637LP5E compared to HMC637ALP5E? Any reliability issue related to HMC637LP5E?