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tech.com
February, 2017
Making a Splash with Water-Resistant Digital Devices
By Doug Clark
THE ENABLING TECHNOLOGY FOR INDUSTRY 4.0
T
he trend in consumer electron- ics has always been to make de- vices faster, smarter, and with
ever-expanding capabilities. But, wa- terproofing has become a new focus of global electronics manufacturers and many brands are rushing to in- clude this benefit to ensure they are not left behind in the marketplace. Since water-resistant standards
play a big role in making expensive handheld and wearable digital de- vices more durable, the industry has adopted the IPX7 rating, which pro- tects against immersion in water for 30 minutes at a depth of 1m (3.3 ft). Yet the critical element in
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meeting or exceeding these higher standards is something most con- sumers are barely aware of — micro-fasteners that must lock out moisture while also complement- ing the aesthetics of the phone, watch or tablet design. Making a device that is eye-catching as well as water-, air- and dust-proof adds incredible value. So far, fulfilling both de-
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mands has proved difficult, since some of the most effective processes for making large, prac- tical 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-re- sistance has led to a discoloration that ruins the appearance of the de- vice’s exterior.
Testing for a Solution A solution that improves relia-
bility while lowering costs was dis- covered using a variable water pres- sure simulation chamber where a combination of water and air pres- sure simulates 1 to 10m (3.3 to 32.8 ft) of water depth. The assembly was conducted
using guidelines set by the Interna- tional Organization for Standardiza- tion (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 tight-
ened 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 or the presence of water was found on the bottom test plate, this would in- dicate a system failure.
Exceeding IPX7 Standards This test was created and exe-
cuted by Sean Riskin, director of en- gineering for the global electronics group at Stanley Engineered Fasten- ing. He then conducted a revealing study that includes his findings after testing nearly a dozen fastener con- figurations of various brands to find the best solutions that meet or ex- ceed IPX7 standards. Most sealants for micro-fasten- ers are a nylon- or Teflon-based sub-
The growing trend for waterproof devices has led manufacturers to explore low-cost solutions.
stance, and there are only two op- tions 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 fas- tened joint. This is because the com- ponents being fastened together are in the path of water before the pro- tective 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 applica- tion process. “You don’t want to spend double
or triple the price on a fastener and not have it look cosmetically pleas- ing,” Riskin says. “In a sense, elec- tronic 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 sec- ondary operation, forcing major man- ufacturers 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 is 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. Both features are second and third operations that are
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