Yet the critical element in meeting or exceeding these higher standards is something most consumers are barely aware of—micro fasteners that must lock out moisture while also complementing the aesthetics of the phone, watch or tablet design. Making devices that are eye-catching as well as water, air and dust proof adds incredible value to a new product.
Fulfilling both demands is proving difficult because some of the most effective processes for making large, practical screws are not suitable for micro fasteners, experts say. As a result, the cost per unit is two or three times higher for the smaller screws. In addition to this, in some cases, overspray of the sealant needed to assure water resistance has led to a discoloration that ruins the appearance of the device’s exterior.
Testing for a solution
A solution that improves reliability while lowering costs was discovered using a variable water pressure simulation chamber where a combination of water and air pressure simulates 1 to 10 meters of water depth. The assembly was conducted using guidelines set by the International Organization for Standardization (ISO) using a minimum of 32 pieces (in this case the M1.0 x 3.0, a common sized screw used in digital devices).
Initially, the screws were tightened to the correct seating torque specifications using a micro torque wrench. (ISO threads = 0.36 Kgf-cm; threads = 0.42 Kgf-cm. A 15 percent increase in torque was added to the threads in order to achieve the same clamp load due to friction.) Water pressure was applied to the head of each fastener to simulate an actual environment that could destroy a portable electronic device (such as a toilet, swimming pool or bathtub).
Once the chamber achieved full pressure, engineers set a timer for 30 minutes and then closely watched the pressure meter and checked for leaks in the dry bottom portion of the chamber. If the pressure dropped and/or the presence of water was found on the bottom test plate, this would indicate a system failure.