Flexible PCB Electrical Test
Downstream operators usually require PCB manufacturers to do 100% electrical testing, so they will agree with PCB manufacturers on test conditions and test methods. Therefore, both parties will clearly define the following:
1. Test data source and format
2. Test conditions such as voltage, current, insulation and connectivity
3. Equipment production methods and selection
4. Test chapter
5. Repair specifications
1. Electrical test
In the production process of the PCB of the flexible circuit, it is inevitable that the external circuit will cause short circuit, open circuit and electric leakage, and the PCB will continue to evolve toward high density, fine pitch and multi-level. Screening bad boards in time, and letting them flow into the process will inevitably result in more cost waste. Therefore, in addition to the improvement of process control, the technology of improving testing can also provide PCB manufacturers with reduced scrap rate and improved products. Rate solution.
In the production process of electronic products, the cost loss caused by sputum has different degrees at each stage, and the earlier the discovery, the lower the cost of remedy.
"The Rule of 10's" is a remediation cost that is often used to assess PCB defects found in different process stages. For example, after the empty board is completed, if the open circuit in the board can be detected in real time, usually only need to make up the line to improve the flaw, or at most lose an empty board; but if the open circuit is not detected, the board is shipped. Until the downstream assembly industry completes the parts installation, but also through the furnace tin and IR remelting, but at this time it is detected that the line has an open circuit, the general downstream assembly industry will ask the empty board manufacturing company to compensate for the parts cost and heavy work cost. , inspection fees, etc. If, more unfortunately, the board's test in the assembly industry is still undetected, and the finished system, such as computers, mobile phones, auto parts, etc., will be found in the test, and the loss will be detected in time. Hundreds, thousands, or even higher. Therefore, the electrical test is for the PCB industry, in order to find the board of the soft line line function defect early.
In the manufacturing process of PCBs for flexible circuits, there are three stages that must be tested:
1. After the inner layer is etched
2. After the outer layer is etched
3. The finished product
Each stage usually has 100% test of 2~3 times, and the bad board is screened for heavy work. Therefore, the test station is also the best source of data collection for analyzing process problems. Through statistical results, the percentage of open circuit, short circuit and other insulation problems can be obtained. After heavy work, the test is performed again. After the data is sorted, the quality control method can be used to find The root cause of the problem is solved.
2. The method and equipment of electrical measurement
Electrical testing methods include: Dedicated, Universal Grid, Flying Probe, E-Beam, Conductive Cloth, and Capacitive. And brush test (ATG-SCAN MAN), the most commonly used equipment are three kinds, respectively, special test machine, universal test machine and flying probe test machine. In order to better understand the functions of various devices, the following will compare the characteristics of the three main devices.
1. Dedicated type (Dedicated) test
The special type of test is special, mainly because the fixture used (Fixture, such as the flexible circuit board for electrical testing of the dial) is only applicable to a material number, board with different material number It cannot be tested and cannot be recycled. In terms of test points, the single panel can be tested at 10,240 points and on both sides within 8,192 points. In terms of test density, the thickness of the probe head is more suitable for the board above pitch.
2. Universal (Universal Grid) test
The basic principle of the general-purpose test is that the layout of the PCB line of the flexible circuit is designed according to the Grid. Generally speaking, the line density refers to the distance of the grid, that is, the pitch (Pitch) (sometimes available) According to the principle of the hole density, the universal test is based on the hole position with a G10 substrate as the Mask. Only the position of the hole can pass the Mask for electrical measurement, so the fixture is easy to manufacture. Fast and the probes are reusable. The universal type test has a standard Grid fixed large dial with many measuring points. The movable probe can be made according to different material numbers. When the production is changed, the different parts can be mass-produced. test. In addition, in order to ensure the smoothness of the completed PCB board line system, it is necessary to perform Open/Short electrical test on the board using a pinch of a specific contact on a general-purpose electric measuring machine using a high-voltage (such as 250V) multi-measurement point. This general-purpose test machine is called "ATE, Automatic Testing Equipment".
The general-purpose test points are usually above 10,000 points. The test density test is called on-grid test. If it is applied to high-density boards, it is off-grid because it is too dense and has been separated from the on-grid design. For the test, the fixture must be specially designed. Generally, the test density of the general-purpose test can reach QFP.
3. Flying probe test
The principle of the flying probe test is very simple. It only requires two probes to move the x, y, and z to test the two end points of each line one by one, so there is no need to make an expensive jig. However, because it is an end point test, the speed is very slow, about 10~40 points/sec, so it is more suitable for samples and small quantities. In terms of test density, the flying probe test can be applied to very high density boards (such as MCM).