PCBA Tech - ICT advantages and disadvantages of PCBA technology?

ICT is mainly used for electrical testing of printed circuit board assembly (PCBA, Printed Circuit Board Assembly). Basically, it can be imagined as an advanced "multimeter" or [LCR meter]. It does not need to remove electronic parts from After the circuit board is removed, the electrical properties of all parts on the circuit board and whether there is an open/short circuit problem in soldering can be detected through the pin points.

The working principle of ICT is to use the Bed of Nails to connect the test points (Test Points) arranged in advance on the circuit board to achieve the purpose of testing individual parts or Nets. Just as the probes need to be placed at both ends of the resistance when taking the resistance on both sides of the three-purpose meter, the ICT must also be measured with a pin point placed on the test point extended by the contact pin of all parts. Sometimes it can also be measured. Imagine a string or partial block of a circuit as a part, and then measure its equivalent resistance, capacitance, and voltage. This can reduce the number of test points. Generally, we call this measurement a Nets test.

Generally, the main defects of PCB assembly are mostly concentrated in welding open circuit, short circuit, offset, missing parts, wrong parts, etc., accounting for more than 90% of the defects. Except for some defects, the rest can be tested by ICT. 100% of the good products are picked out wrong. The "offset" may not be detected by ICT electrical measurement, because as long as the part feet are still welded to the position, the electrical test cannot be detected if there is no abnormality.

In fact, it remains to be seen whether such defects are bad. The room for further clarification is not necessarily bad. In addition, the intermittent phenomenon caused by cold/false soldering may not be 100% picked out by ICT. This should be the most troublesome place, because ICT uses electrical testing to detect circuits. When the solder joint is still in contact, it cannot be detected.

So ICT can basically detect the following functions or parts:

▪ Open, short.

▪ Detect wrong parts, missing parts, tombstones, bridges, reverse polarity.

▪ can measure resistance (resister), capacitance (capacitor), inductance (Inductor), transistor, diode (diode), stabilized diode, triode measurement (triode) photocoupler, relay, field effect electricity Crystal test (FET), IC, connector and other parts.

▪ Through TestJet, it is possible to measure the open and short circuit of the PIN connector or the IC parts with the solder pins on the outside without the need of pin points.

▪ DC/AC voltage measurement and frequency measurement.

▪ Electrical function test. You can run low-level programs (such as BIOS) for self-testing.

▪ You can use【Boundary-scan/JTAG】to test the function of active parts.

▪ can automatically download software or operating system to the memory of the circuit board.

The advantages of using ICT to test circuit boards:

▪ The test speed is fast and the time is short. PCBA can do L/C/R/D tests without powering on, which can effectively reduce the waiting time for the test to start, and it can also reduce the accidents of circuit board burnout caused by short circuits. A circuit board assembled with 300 parts, the test time may be as short as 3 to 5 seconds to complete the test.

▪ Excellent retestability. Controlled by a computer program and accurately measured, it greatly reduces the risk of misjudgment and missed measurement, and reduces the troubles of the production line. (If the test point has poor contact, it may cause misjudgment)

▪ The on-site technical dependence is low. Because almost the whole process is controlled by computer, it greatly reduces the time and error of human operation. With a little training, ordinary operators can easily operate the equipment and can replace the test fixture by themselves. (The test program must be maintained by a professional technician or engineer).

▪ Product repair costs are greatly reduced. General operators can be responsible for product maintenance, effectively reducing personnel costs. ICT can tell which part or which Net has a problem through a computer program, which greatly reduces the speed for technicians to re-measure and remove bugs.

▪ Improve product throughput (through put). Through rapid testing, real-time feedback of problems to the front-end SMT operation can reduce the defective rate of production, reduce the stock inventory and the accumulation of defective products, and also reduce costs and improve competitiveness.

Improve product quality. As long as there are enough test points, ICT can measure all the circuits and parts on the circuit board, and even the parts on the by-pass circuit can be measured, which can improve product quality, reduce customer complaints, and even improve Performance.

Disadvantages of ICT circuit testing:

▪ The cost of ICT equipment and fixtures is generally very expensive, especially for pneumatic steel fixtures, which sometimes cost NT$400,000 to NT$500,000, which is more suitable for mass-produced products.

▪ When using ICT testing, it is necessary to design additional test points (Test Point) on the circuit board to connect the needle bed. Reduce the utilization rate of circuit board wiring.

▪ The test point sometimes has different poor contact problems due to different surface treatment methods. For example, the OSP board needs to be printed with solder paste on the test points to achieve the purpose of contacting the conductor, but the solder paste on the solder paste can easily form a protective film, causing poor contact.

▪ The needle bed needs regular maintenance, and the probe needs to be replaced regularly to ensure the normal operation of its mechanism and probe.

What is the difference between ICT (In-Circuit-test), MDA (Manufacturing Defects Analyzer), and ATE (Automatic Test Equipment)?

▪ MDA is generally called a relatively low-level ICT, such as TRI-518 series, JET-300, ADSYS-K518 series... etc. This type of testing machine can only measure basic L/C/R/D parts, and can also be matched TestJet test row PIN parts, but its function is relatively young and can not provide power for the circuit board to be tested, so it can not perform low-level circuit board program self-test. This kind of testing machine can be regarded as a multimeter that can be automatically tested.

▪ In general, what we call ICT refers to this higher-level test machine, such as Agilent3070, Genrad, TR8100... etc. In addition to the basic MDA functions, you can also download the program to the circuit board on the side to perform self-testing and provide Voltage and frequency measurement...etc.

▪ ATE is usually a streamline test, which can be directly connected to the back of the SMT. Its main purpose is to test whether the functions of the PCB real board and on-board parts are working properly, so the real board must be powered on to make the parts on the board work, so When ATE sends signals, special consideration must be given to the characteristics and specifications of the PCB parts, otherwise the parts are easily damaged.