A handheld ultrasound probe that costs more than the car it travels in does not fail in a dramatic way. It fails quietly: a lens array drifts out of alignment after two years of van transport, and the service engineer finds nothing obvious to point at. That was the problem our engineering bench was asked to solve last quarter for a European distributor shipping point-of-care diagnostic kits to 300 clinics, and the answer was not thicker foam.
What sensitive devices actually need
Two things damage portable diagnostic equipment in transit. The first is a single high-g shock, typically a 0.5-1.2 m drop onto a corner. The second is low-level vibration over hours of road transport, which frets connectors and loosens optical benches. A case has to handle both, which is why we build the insert as a two-layer system: a 6-10 mm die-cut EVA foam cradle at 55-70 kg/m3 holding the device at its rigid points, wrapped by an outer shell of 4-5 mm molded EVA at Shore C 45-55. The cradle is cut with 15-25 percent compression allowance so the device is gripped rather than resting, and the lid carries egg-crate foam with 8 mm peaks that touch nothing when the case is closed but take the load when it is stacked. The same cradle geometry runs across the EVA case category when a customer has more than one device to protect.
Testing before shipping, not after
Every new medical shell goes through drop and vibration work before the tooling is released. Standard protocol here is six faces, three drops per face from 1.0-1.2 m onto concrete, followed by a random vibration profile run to ASTM D4169 assurance level II and an ISTA 3A sequence for parcel shipments. The device is instrumented with a shock logger on the first drop series, and we look at peak G on the cradle: if the reading goes above roughly 40-50 G for a precision optical assembly, the foam density goes up and the test is repeated. Nothing ships on a drawing alone.
Temperature is the other half of the problem. For reagent kits and insulin, the shell becomes an insulated carrier: 8-10 mm EVA plus a 5 mm closed-cell PE liner and two 200 g gel packs holds 2-8 C for roughly 6-10 hours at 25 C ambient, verified in a chamber rather than estimated. Our EVA medical case range covers both the rigid instrument format and the insulated carrier format on the same production line.
Zippers, seams and the parts that get overlooked
On a shockproof build, the zipper is usually the first thing to go, not the foam. We specify a #5 or #8 reverse coil with a storm flap, and the slider is run to 5,000 cycles. Seams are bar-tacked at every handle and webbing attachment, because a handle that tears off at an airport is a shock event the foam never sees. Material files are kept against the RoHS and REACH substance lists, with CTI test reports available per batch, which is what importing distributors in Germany and Japan ask for when they register a kit.
Current production on this line is running 900 insulated diagnostic carriers a month for two OEM accounts, with die-cut inserts changed over between batches in about 40 minutes. Orders start at 500 pieces and sample turnaround is around three days for a shell of this type, and the engineering team keeps the drop-test video and logger files on hand for customers who want to see the numbers before signing.