Even partial tenting using a liquid photoimageable (LPI) solder mask will cause contact problems, as the mask liquid will tend to run away through the via hole. Tenting a testpoint-designated via will effectively block test probe contact. Careful consideration should be given to any via tenting requirements of the design.A well-honed and adaptable testpoint policy will allow different designs to be tested efficiently and cost-effectively. The best philosophy is to develop a methodology that will result in generic testability. The more non-standard and complex your pattern of testpoints, the more costly it will be to configure a fixture with which to test the board.The reason for this lies in the fact that a dual-head test fixture incurs greater cost than a single-head test fixture. It is advisable to locate all testpoints on one side of the board only, using vias to achieve this if necessary.This should be taken into consideration when planning testpoint locations for assembled board testing. A testpoint underneath a component (on the same side of the board as the component) is usually used at the bare-board testing stage.For example, will the board be probed from the bottom side only, the top side only, or both sides. When choosing the side of the board that testpoints will be allowed on, consideration should be given to the testing processes and associated fixtures that will be used.The following are just some pointers to consider when defining a strategy to incorporate testpoints into a design: Considering Your Testpoint Strategyīefore jumping into the assignation of pads and vias for use as testpoint locations, it is a good idea to step back and think about what is required. Testpoints can be assigned manually or, in a more streamlined and automated fashion, using the Testpoint Manager. As the board is populated, you may no longer have probe access to component pads and certainly no access to pads and vias under a component!Īltium Designer provides a powerful system to handle your testpoint needs and enhance the testability of your boards, allowing you to separately assign testpoints for bare-board fabrication testing and/or in-circuit assembly testing as required. The locations used for testpoints when performing in-circuit assembly testing however, will almost always be different. For example, when performing bare-board fabrication testing, the board is not populated and so all pads and vias are 'fair game' when it comes to assigning testpoints. The location of testpoints on a board will depend on factors including the mode of testing (including bare-board fabrication testing, in-circuit assembly testing, etc.) and the method of testing (including automated testing using flying probe and bed-of-nails fixtures, hand testing, etc.). To aide in this process, it is fundamentally beneficial to have a scheme of points on the board – testpoints – which the testing equipment can probe and perform the required tests. Once fully populated with all its components, a board is often tested again to ensure signal integrity and device operation. After fabrication, the board is typically tested to ensure no short or open circuits. Testing is an important part of the board manufacturing process.
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