FCT in an Electronics Manufacturing Service company – What is it?

An electrical function test (FCT)  – also frequently called an End of Line test (EOL test) – is a test in the electronic manufacturing service industry that consists of testing an assembly’s functional performance.  The electrical function tester will apply inputs to simulate the board’s expected inputs in the end user’s application.  A functional tester will measure, via a variety of means, the board’s response to the stimuli.  The board’s responses will be compared to the expected responses.  Boards will be deemed as test failures that don’t respond correctly.

This quote from a post (found here) on Assembly Magazine’s website describes functional testing well:

“By the time you get up to the functional tester, you are testing functionality of the product. You’re not testing whether the board is good or not. You’re not testing whether the solder is there or not. And you’re not testing whether the parts are within tolerance or not. What you’re testing is whether it works as it should.”

What is meant by End of Line (EOL) Testing?

You may be wondering why functional testing (FCT) is frequently referred to as “end of line” testing.  The last step we perform before packing a unit into a box is to electrically function test it. This gives us great assurance that the manufactured board will be deemed good by our customer.  Since functional testing is the last step, it is frequently referred to as “End of Line” testing (EOL testing).

How is FCT different than ICT (In-circuit Testing)?

Electronic manufacturing service companies use In-circuit testers (ICT) mainly check for shorts, opens, reversed components, and wrong components on a PCB.  FCT testing can also detect some shorts and opens but it falls way short of being able to detect component issues on a board (such as wrong component values, polarity issues, etc.) the way ICT can.  This is because an ICT is frequently known as a “bed of nails” tester due to is high utilization of probing pins.  These probing pins are placed in a fixture so that, on a well-designed PCB, nearly every electrical net can be probed.  An ICT can easily locate defective components due to this mass of probes.

A functional test fixture (FCT fixture) typically has a fraction of the probe pins that an ICT fixture has.  FCT fixtures mainly have their probe pins located to probe locations (usually connector pins) that will be used in the customer’s application.  This is because we want to test the functionality of a board as it would be used in the end user’s application.

Electrical Functional Testing methods at Futaba

Futaba is pleased to work with our customers in a variety of means with respect to electrical functional testing.  We have worked with customers in the following ways:

  • Customer does not want FCT.
  • Everything needed for FCT is supplied by the customer.
  • Only the test requirements/specification is provided by the customer.
  • Customer would like FCT but provides nothing.

I’ll go over these 4 scenarios.

Customer doesn’t want Electrical Function Testing

We have built boards for some of our customers that were both very simple to manufacture and consisted of inexpensive components.  These customers wanted to pay the least amount possible for us to manufacture their boards.  Since functional testing is an added process step, the cost for us to manufacture the board will be higher than if we did not perform functional testing.  Because the boards were simple to manufacture, and since we have great quality, these customers chose to forgo electrical functional testing in order to pay less per board.  These customers were willing to risk obtaining a defective board from us at their cost in order to get the lowest manufactured price possible.  Such customers typically had their own test equipment at their facility that would allow them to catch any defective board that they might receive from us.

Everything needed for FCT is supplied by the customer.

Approximately 20% of our customers supply everything (hardware and test software) we need to functionally test their boards.

For such customers, we have only one request: incorporate into their test, software that we developed and provide freely.   Our software allows their tester to integrate with our production database, which we call the “Tracking System”.  We have never had a customer deny our request.  Why?  Because we can tract functional test results throughout of our manufacturing process as a result. This traceability allows us to detect units that failed or skipped our customer’s electrical function test.

Only the test specification is provided by the customer.

More than 75% of our customers fall in this category. These customers will give us a document that describes how we are to functionally test their module.  The specification will tell us how to operate the module and what are the module’s expected responses.

Of the 4 testing scenarios mentioned in this section, Futaba likes this one the best.  You may be thinking, “Why would Futaba want to build a tester for our board instead of letting us build one for them?”  The biggest reason is less potential downtime.   Futaba has over 10 electrical function testers that are identical that are full of various kinds of test equipment.  These testers are generic enough that they can be used to test nearly everything we build.  If an electrical function tester were to go down, we could simply remove the test fixture from it,  plug it up to a different functional tester, and keep producing.

When a customer-supplied a functional tester goes down, we have no other testers to move production to and would have to get phone support from the customer if our technicians or engineers could not locate the problem.  If we needed to contact the customer for support during our 2nd shift operations, we may find that the customer has no 2nd Shift personnel to assist us.

Customer wants an electrical function test but provides nothing

Currently, approximately 5% of our customers fall in this category.  These customers are typically either startups or they are in a prototype/proof-of-concept stage.  Such customers have spent all their resources designing the product and not had time to think about test requirements.  For such customers, our team of Test Engineers will study the schematic and any supporting documentation.  From there we can develop an electrical function test.