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October, 2017 Creating ESD-Safe Test Fixtures By Matthias Zapatka, CTO, INGUN USA


discharge) coats, wristbands, shoe covers, and even disposable ESD hairnets, all protect devices under test and their surroundings from ESD.


W


alking onto the production floor of big con- tract manufacturers often feels like enter- ing an operating room. ESD (electrostatic


ESD Protection Fixture kit suppliers usually offer both stan-


dard and ESD versions of their products. Usage of such ESD fixtures has become the norm, especial- ly in the automotive sector. INGUN is now offering a manually-activated test fixture with ESD protection features. Probe plates are usually made of FR4 or


G10 which both have a surface resist- ance of 1012W. The materials act as insu- lators. To make their surfaces dissipa- tive and thus capable of discharging, they can be coated with dissipative paint.


For side plates and the fixture


frame, ADAPTONIT-laminate can be used instead of regular (insulating) materials. Also, the pressure-frame plates (Lexan) can be impregnated with ESD materials. The company can also make ESD-


Fixture ESD control: tying all components together. Even with all the precautions for humans, we


sometimes simply forget to properly protect the test equipment as well. In the high-volume produc- tion world, mechanical test fixtures are used for in- circuit (ICT) and functional testing (FCT). Test probes, mainly the spring-loaded type, make con- tact with a PCB assembly as the test fixture is actuated. This can be done either by closing a clamshell lid by hand, by a pneumatic actuator or with vacuum. In theory, that all works fine, but in practice the DUT can suffer damage easily. Quite often when testing, the board is not yet installed in its final enclosure. Thus the components are exposed and can be touched by hand or can come in contact with the fixture or parts that are not pro- tected against ESD.


safe rubber gaskets and seals for vacuum test fixtures, through addition of a prod- uct called Naftoflex. Pushrods made of aluminum, but with a Delrin or Teflon


tip, are also available. All these materials bring the surface resistance down to 102 to 1010W, depending on the material. At this resistance the material is then dissipative and can discharge voltage. In order for the test fixture to function prop-


erly with regard to ESD, all dissipative parts must be tied together and routed to a grounding bar. ESD protection is no substitute for regular electri- cal grounding, as the discharged current goes through a resistance in the megohm range. Therefore, additional grounding methods and safe- ty features, such as locking mechanisms, finger guards etc., have to be used for applications with lethal electrical charges.


Grounding to the EBP (earth bonding point).


bar sending technique” (ATSM Standard D257). All these tests are carried out by INGUN prior to ship- ment to ensure that its fixture product line meets even the most strict specifications for automotive


and other sensitive applications. Contact: INGUN USA, Inc., 252 Latitude


Lane, Suite 105-106, Lake Wylie, SC 29710 % 803-831-1200 fax: 803-656-5080 E-mail: mailbox@ingun.us Web: www.ingun.us r


See at productronica, Hall A1 Booth 359 For proper ESD protection, the operator


should use a wristband and connect it to the test fix- ture frame. To ensure full functionality, a field strength meter can be used. An electrostatically charged plastic film can be used on all the materials and after 20 seconds the field strength recorded. According to DIN EN-61340-5-1 the residual charge must be less than 50 V/cm. To check for resistance, surface resistivity meters are used with a “parallel


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