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Short Description: PCB Design guidelines for test with mechanical in-circuit fixture. Page 2 of 3. 2.8 A round free area with radius 0.060 inch from the center of test pad ...
Content Inside: PCB Design guidelines for test with mechanical in-circuit fixture. Introduction This guideline is written for PCB designer. Testability consideration becomes more and more important on the electronic industrially today. In order to increasing testability. Following guidelines should be take into consideration when design PCB if mechanical fixture is using in one of test procedures of the product. There are two parts in the guideline, the first part considers to the probing, the second part for electrical test circuit. Probing Consideration 1. Precise tooling (datum) holes. 1.1 At least two datum holes must be provided on the device under test (DUT). The two datum holes should be on the opposite diagonal corner of the DUT. 1.2 The minimum diameter of the datum should be 0.125 inch (3.1 mm), in order to maintain a stable precision reference. 1.3 Diameter tolerances should be held at +0.002/-0.000 inch ( +0.08/ - 0.00mm). 1.4 Metal plating are NOT suitable for datum holes, the plating will affect the precision of the hole. 1.5 Datum holes to pad/feature tolerance should be control under 0.002 inch (0.05mm). 2. Probing Target 2.1 All probing target (test pad, via's and component lead) are preferred to be on one side of DUT. 2.2 Probing target should not be place in the 0.125 inch (3.2mm) round area of datum holes. 2.3 The minimum diameter of probing target is 0.035 inch. If both side probing is required, the upper side-probing target diameter should be a minimum 0.040 inch (1.0 mm). 2.4 Center to center spacing between test pads should be a minimum 0.075 inch, for an ideal spacing it should at 0.100 inch. Possehl is capable to reduce the spacing to 0.050 inch, but it is highly depending on the other conditions of the PCB. Possehl can not guarantee 0.050 inch spacing is work on all PCBs. 2.5 Test targets should be at least 0.125 inch away from the PCB edge or "break-away" areas. 2.6 The component's height on the same side of test pads should not be greater than 0.255 inch (6.4mm). Additional machining on the fixture nail plate is required if tall component is install in DUT, in such way the mechanical strength of the fixture will be reduced. 2.7 Probing targets should keep away from the area of PCB that required masking tape or glue during soldering.