A brief discussion on the manufacturing strategy of test fixtures

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A brief discussion on the manufacturing strategy of test fixtures [Copy link]

A brief discussion on the manufacturing strategy of test fixtures

【Source: SMT Forum Network】【Author: skyline82】【Time: 2005-8-2 9:09:48】【Click: 3724】

As printed circuit board technology develops toward multi-layer, fine-line, small-hole, and high-density (which has already arrived and is rapidly becoming popular), the circuit board manufacturing process has also brought new challenges to the testing field. Below I will talk about the relevant technologies and strategies for testing in manufacturing in this industry from several aspects. 1. Test cost control At present, the finished product testing methods in this industry mainly include: fixture testing (divided into composite and special types), flying probe testing, and automatic optical testing. The test cost is mainly the cost of test equipment selection and production materials. 1. The relationship between equipment selection and cost control. Different manufacturers have different order structures, and the order structure largely restricts equipment selection. The biggest advantage of flying probe testing is its fast market response and extremely low cost, but the detection speed is slow. Generally, it takes three to ten minutes to detect a shipping unit, which is suitable for testing samples and small batch orders. If the customer requires a sample, flying probe testing can be selected until the customer places a batch order and then changes to fixture testing, which saves the cost of fixture production during the customer's change process or cancellation of the order. 2. Save costs by designing test methods and process strategies. When designing a test method and process strategy, countless variables must be taken into account. At this time, different test methods and production methods must be selected according to different situations. The production cost of a high-density PCB test fixture is very different from that of an ordinary PCB test fixture (depending on the size and number of probes). Ordinary ones cost hundreds or thousands of yuan, while common high-density ones cost thousands or even tens of thousands of yuan. At this time, you can consider using conductive adhesive strips instead of expensive small probes. As far as I know, the cost of a set of probes with a diameter of 0.45 (four zeros) seems to be about 18 yuan, and a BGA position usually has 100 to 300 test points. Using conductive adhesive only costs one cylinder (one or two hundred yuan) for one BGA position. However, there is a disadvantage of conductive adhesive testing, that is, if two independent IC positions are short-circuited, it cannot be tested. Gold plates generally do not have IC position short-circuits, but tin plates will have them if the hot air leveling is not well controlled. When making fixtures, you can sometimes consider multiple tests for one shipping unit and one test for multiple units, which I often encounter. For example: there are nine units in a SET, and the cost of fixture materials is about 12,000 yuan. This batch of orders belongs to a small batch of multi-model customers. At this time, you can choose to test three units in three times. The cost is saved by two-thirds, and the delivery time can also be guaranteed. Another example: a batch of large orders has a short delivery period, and the shipping unit is too small to be conducive to the test speed. At this time, you can consider testing the entire board in rows before printing the solder mask. In addition, if the repair board is not visible in the final inspection after printing white or black ink, it is necessary to test twice to ensure rework. These are all strategies for testing cost control. As calculated above, the cost saved by rational testing process technology in cost control is amazing! 2. Test Optimization In fact, I have mentioned optimization from the perspective of cost above, which is mainly cost optimization and process design optimization. Here I will mainly talk about the optimization of test tool production. 1. Production of test data. Flying probe test data is relatively simple. Usually, the key is whether the network analysis is correct or not. Secondly, the number of test points and the number of networks determine the detection time. Generally, optimizing the number of test points of the same network has little effect on the test speed. The data for making fixtures has very high production requirements. Usually, it is easy to miss or over-select points when using CAM software to make data. The production speed will be much slower when there are many layers (I used V2001 software to select points before. It was really a headache when I encountered more than 6 layers of boards. In order to avoid missing points, I would select more points). At present, many large manufacturers have purchased special production and testing software, which will speed up the production and testing much faster, without manual point division, and the maintenance will also be much faster. 2. Production of test fixtures. Production of test fixtures is also a tedious process. From material arrangement, inspection after drilling, winding, needle placement to installation and debugging, carefulness and patience are required to produce high-level fixtures. Among them, checking the drilling accuracy is very important. When encountering dense small holes, drilling one hole off may cause the entire fixture to be disassembled and remade. Controlling this step is the key to optimizing fixture production. Secondly, consider integrating multiple drilling data, especially the data integration when drilling conductive glue, so as to reduce the complexity and tediousness of drilling for drilling operators and reduce errors. In summary, the optimization of the test can actually solve a lot of problems by improving the software. In addition, improving the engineering technology and skills of technicians will also play an optimization role. 3. Common problems and solutions in mold making There are some common problems in the production process of test fixtures. At this time, it is necessary to analyze and solve them. 1. The hole is drilled off-center, causing the test probe to fail to contact the correct position, resulting in a false open short circuit. Countermeasures: This usually occurs on small holes. Before making the mold, visually check the drilling accuracy to see if there is a deviation in the hole. If the hole is found to be off-center, re-drill it with a high-precision drill. If conditions permit, drill it out together with the red film and check the film for deviation. 2. When debugging the mold, the missed point is found. Countermeasure: Use a board or film to shoot on the mold, manually drill the missed hole, add the winding to the network and re-read the board for debugging. If the missed point is at the dense hole, this method is very difficult. 3. The hole measurement point is drilled too large, resulting in the probe not being able to contact the welding ring, resulting in a false open circuit. Countermeasure: If there are only a few, you can plug the original drill hole with a real object, and then manually drill out the appropriate hole diameter. This method is also applicable to changes in customer information and a few measurement points, which can avoid re-production. 4. There are too many test points for the test machine to test. Countermeasure: Make two fixtures for the network and test twice. 5. The mold with conductive rubber strip has false short circuit or is difficult to PASS. Countermeasure: Check whether the conductive rubber strip has been used for too long and has become flat or crooked (usually due to this reason), and replace the conductive rubber strip.

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This method is also applicable when customer information changes and only a few measuring points change, thus eliminating the need for re-production.