PCB News - PCB process ICT (In-Circuit-Test) circuit electrical test is really cheaper?

PCB process ICT (In-Circuit-Test) circuit electrical test is really cheaper?

It's really here again. Every time a big boss comes up, he will re-examine whether the test can be taken away? Issues, especially the ICT (In-Circuit-Test, circuit test) process that requires a lot of money to purchase equipment and fixtures and has no production value (because testing does not increase output) has always been a thorn in the eyes of big bosses .

But in the real world, do you really dare to ship products directly to customers without tested products? These big bosses always know how to urge their subordinates to do it, but they are unwilling to make a decision.

When our subordinates tried their best and were rejected, the final showdown asked the big boss to pick a product by himself and personally order all tests to be taken down to see how the results are. Of course, the purpose is not to hope all the benefits (saving shipping time), Reduce production costs) are taken away by the boss, and after a problem (customers complain about poor product quality), subordinates are required to take the blame, but by this time almost all the big bosses will stop.

However, there are also some big bosses who are unwilling to let go. They will continue to throw some problems and continue to torture you. For example, they will ask you: Since both ICT and FVT are tests, can you remove ICT and replace them with FVT? Okay?

This returns to the old question. Before answering this question, it may be necessary to explain the test process after the circuit board is assembled. Generally, after the traditional circuit board is assembled by SMT, AOI (Auto Optical Inspection) is usually used to check the offset, short circuit, tombstone, missing parts... and other problems with optics, and then go through the circuit test of ICT or MDA. Finally, through FVT (Functional Verification Tester) function test and other three methods to confirm the function of the circuit board is normal.

Next, we need to understand the test difference between ICT and FVT?

Here is an attempt to list the test differences between ICT and FVT. Please note that the comparison is ICT instead of MDA:

Do you need to power on and start the test? It can be tested without powering on the PCBA board to be tested, which can avoid the risk of circuit board burnout. Then power on when you want to perform a low-level trial test. The test must be powered on, and the circuit board may be burned out due to a short circuit of parts.

Do you need test points? All test points are used for testing, but Nets can be used to reduce the number of test points. Only need some test points, or use real plug-in method to link IO devices (display, network cable or card reader)

Defective product debugging ease As long as there are test points, it can accurately point out which part or node has a problem, and it is convenient for the operator to repair the defective board. There is no way to tell exactly which part is faulty. You can only use experience or hire a professional repair technician to repair the defective board.

Bypass circuit test capability As long as there are test points, the bypass circuit can also be tested. Unless special conditions can be simulated, it is difficult to test and confirm the quality of the bypass circuit.

Short/Open test for all of the nets. (Open and short circuit test for nodes or parts) As long as there are test points, all parts or nodes can be tested for open and short circuit. The product function can only be tested by powering on and booting.

Components for L, C, R, D, Tr (measure the characteristic values of inductance, capacitance, resistance, diode, and transistor) As long as there are test points, all passive component characteristics can be measured. The product function can only be tested by powering on and booting. If there is a wrong part or the feature is missing, it may not be detectable.

Active component (IC) characteristic measurement can use test point measurement, or use JTAG or TestJet to reduce the number of test points. Check the product function by powering on it.

Measuring Frequency, Voltage. Yes. Can.

Performing the Function test. It can perform low-level functional self-test. It can only detect most of the functions, but it is not possible to check whether the screen display is normal and whether the IO reading is correct, because it is not a real insertion. All functions can be tested once using test points or plug-in tests, but only functions under normal conditions can be tested.

Test time Generally, a board can be tested within one minute, even as short as 10 seconds. Generally speaking, it may take several minutes for a board to be tested, because some human operations cannot be avoided.

Do you need to download the test program first? You can perform open and short circuit and passive component characteristic tests without downloading the test program. If you want to perform low-level program testing, you need to install or download it in advance. You need to download the operating system and test program in advance to start the test.

Do you support OTG downloading program? You can download the operating system or program to the memory of the circuit board.) Support.

Actual comparison of the test time and labor cost of [ICT+Sampling FVT] and [Pure FVT]

Here, the same board is used to compare the test time difference between [100% ICT+5% sampling FVT] and [No ICT+100% FVT]. This data will be different for each company’s results and projects. The data here is only for reference. The reason why [5% FVT sampling] is used is because there is a complete machine test to cover later.

The result of the comparison shows that the test time of [No ICT+100% FVT] took 310 seconds in total, while [100% ICT+5% FVT] only took 67 seconds. Assuming that the hourly working hours of the factory are US$10 and the output of 100,000 pieces per month, the monthly working hours will be US$67,500 (=86100-18600).

ICT+5%FVT sampling NO ICT+100%FVT
Short/Open test for all the nets 20s 0
Components for L,C,R,D, Tr 0
Measuring Frequency, Voltage 30s
Performing the Function as FVT 35s 245s
Loading OS 35s
Additional 5% FVT sampling 12s 0
Total Testing Time 67s 310s
Dollar charge by Factory
(Support US$10/hour) US$0.186 US$0.861
Monthly spend
(Support 100,000 output per moth) US$18,600 US$86,100

Calculation result: using ICT test saves money than using FVT alone

If you still don’t understand the above calculations, let’s use the actual amount spent below to let you know more about the difference in factory costs for using ICT or not.

100%ICT+
5% sampling FVT without ICT+
100% FVT amount difference
ICT or FVT fixture cost 153,000 53,000
Circuit board testing cost per month 18,600 86,100
Fixture cost in the first month + test man-hour cost 171,600 139,100 32,500
Fixture cost in the second month + test man-hour cost 190,200 225,200 -35,000
Fixture cost in the third month + test man-hour cost 208,800 311,300 -102,500
Fixture cost + test man-hour cost for the fourth month 227,400 397,400 -170,000
Fixture cost + test man-hour cost for the fifth month 246,000 483,500 -237,500
Fixture cost for the sixth month + test man-hour cost 264,600 569,600 -305,000

The above calculation results show that in the first month, the amount spent on [No ICT + 100% FVT] is less than that of [100% ICT + 5% sampled FVT], and it is reversed after the second month. By the sixth month, the cost of using ICT has even saved US$305,000 compared with not using ICT.

So you should already know whether ICT is used or not, but as mentioned before, ICT is basically more suitable for mass-produced models. If there are fewer active parts such as IC s in the world or there are not so many ICs and other active parts on the board, maybe As long as the MDA is used, if it is a board that produces less than 1,000 pieces a month, you can even consider using only AOI and FVT for testing.