Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


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ICT | 10 March, 2007

i want to know what is the difference between ICT and functional it mondatary to in ICT to test all components or there is a basic rules ,to know what are things to be tested . thanks ,

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ICT | 10 March, 2007

Here's your test definitions [clipped from the dictionary in the fine SMTnet Library]: * Test, Automated. Computer controlled electrical testing of parts, assemblies, or finished products. * Test, Built-In (BIT). An electrical testing technique which adds hardware to the chip to allow the integrated circuit to test itself with minimal use of test equipment. * Test, Combinational. A test method that uses automatic test equipment to measure component parameters (i.e., in-circuit testing) and performance (i.e., functional testing). * Test Fixture. Equipment that interfaces between test equipment and the unit being tested. * Test, Functional. An electrical test of an assembly under actual operating conditions. * Test, In-Circuit (ICT). An automated test method that measures parameters such as continuity and short and open circuits on an assembled printed circuit board. It also tests components mounted on the printed circuit board. * Test, Manufacturing Defects Analyzer (MDA). An automated test that measures component values, but does not supply power to the printed circuit board.

Q. Is it mondatary to in ICT to test all components or there is a basic rules, to know what are things to be tested? A. Generally, the fault coverage in ICT for a fairly complex board is around 50 to 60 percent. Fault coverage is limited: * Purposely to control upfront programming and fixturization cost and oning test time. * By the capabilities of the tester.

There are no rules. Programmers decide based on the conflicting needs to prove a board to limit cost.

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ICT | 12 March, 2007

ICT is generally a manufacturing verification test. Coverages vary depending on the board. I've run lots with as low as 25% coverage on the board (but produced 98% FPY post board assembly).

Functional test is exactly what it sounds like. Checking the function of the board.

Neither test should be considered 100%.

ICT designers will typically design fixtures/programs to test 100% of available nets on the board. This does not mean 100% components/circuitry, however, as often times circuit nets are not 100% available. A Test Engineer will then adjust the testing parameters based upon an actual boards. Some items that can mess with ICT testing resulting in tests being disabled are RC circuits, LR circuits, parallel resistors, etc. Active circuits can give variable results which make it near to impossible to get consistently repeatable results, so a Test Engineer will opt to disable those parts of the test.

Every product is different; but the important thing to remember is that just because a product passes in-circuit test, doesn't mean that it will work; or that it will be a correctly built board. ICT is a manufacturing verification test, that is, it verifies placement, shorts/opens, and value of discreet parts. More advanced testers can exercise IC's by passing data-bits through them, and reading the outputs.

I guess I'm saying it's not a catch-all in manufacturing; though, it can be a life-saver when you're running 5000 boards, and find out that there's a wrong value resistor installed on the first 100!

cheers ..rob

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ICT | 17 March, 2007

waht are the things to take on consideraton that enable injecting signals to devices to be tested in such a way that the currnet will be driven directly to that device ruther split to the neighboring devices . thanks

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ICT | 17 March, 2007

Guards are used to limit the interaction between circuits. Look here:

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