Waterproofing is claimed to be the new focus of global electronics manufacturers. Since water-resistant standards play a big role in making expensive handheld and wearable digital devices more durable, the industry has adopted the IPX7 rating, which protects against immersion in water for 30 minutes at a depth of 1 meter (3.28 feet).
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.
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. 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 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.
The test was created and executed by Sean Riskin, Director of Engineering for the Global Electronics Group at STANLEY Engineered Fastening. Afterward he created a revealing study that includes his findings that tested nearly a dozen fastener configurations of various brands to find the best solutions that meet or exceed IPX7 standards.
Most sealants for micro fasteners are a nylon or Teflon-based substance, and there are only two options for applying the protection. Manufacturers either seal the threads, or seal underneath the head of the screw. Both have advantages and disadvantages.
Sealing just the threads may not protect the multiple layers of components that are in a typical fastened joint. This is because the components being fastened together are in the path of water before the protective sealant. Sealing under the head is preferable because it is the first barrier against moisture. Yet this is the method that, in some cases, results in an overspray and discoloration caused by the application process.
“You don’t want to spend double or triple the price on a fastener and not have it look cosmetically pleasing,” Riskin says. “In a sense, electronic manufacturers are struggling with a three-way battle. Function versus beauty versus cost.”
Also, the sealant is what creates prohibitive costs because it must be applied to every single unit as a secondary operation, forcing major manufacturers to spend upwards of tens of millions of dollars annually just on micro fasteners alone.
But what if the sealant could be eliminated from the equation? That’s easier said than done.
The sealant creates a water and dust barrier and, in addition, the screws must have an anti-vibration feature applied so that it won’t loosen and back out during normal use of the device.
The solution Riskin was looking for came from the combination of under head design features of screws and Spiralock, a subsidiary of STANLEY, which years ago developed and re-engineered a female thread profile that adds a unique 30-degree wedge ramp at the root of the thread and mates with standard 60-degree male thread fasteners. This innovation removes the need for nylon-based patches or other anti-vibration countermeasures and therefore significantly reduces the cost of fasteners.
Riskin’s study revealed other advantages, too. When torqued to specifications, standard screws are not perfectly perpendicular; most are a couple of degrees off-access and therefore provide a gap where fluid can enter.
The Spiralock thread profile, in comparison, is self-centering and the head of the fastener is perpendicular to the bearing surface. Riskin knew that this alone would not entirely seal out moisture, so he added an 87-degree under head feature and semi-flat head to the micro fasteners. Although the head designs have been available for years, this is the first time they’ve been combined with Spiralock’s modified locking thread profile to create excellent moisture sealing joints that exceeds the IXP7 rating standards.
It also creates a vibration-proof joint that is easy to assemble, thus saving digital device brands time and money.