PCBA Tech - About SMT manufacturing process first inspection system

In the SMT manufacturing process, there is a practical error prevention method that can reduce the risk of wrong parts, reduce the probability of errors, and effectively improve the quality of the entire production process. This type of method is the first mechanism.

The so-called first piece mechanism is to make a prototype before the formal production and processing. This board will carry out a full range of inspections. After all the inspections are passed, the formal production and processing will begin. The first production is generally under the following conditions Carried out:

1 Start of each work class

2. Replace the operator

3. Replace or adjust equipment and process equipment. (Replace the stencil, replace the model)

4. Change technical conditions, process methods and process parameters

5. After selecting new materials or substituting materials. (Such as material changes during processing, etc.)

A reasonable first-piece mechanism can ensure that the components waiting to be installed on the placement machine are correct, the state of the solder paste used, and the furnace temperature are no problems. It can effectively prevent the occurrence of batch defects. The first mechanism is a means to control the product manufacturing process in advance, an important method of product process quality control, and a practical and indispensable method for companies to ensure product quality and increase economic benefits.

Long-term practical experience has proved that the first inspection system is an effective measure to find problems as early as possible and prevent products from being scrapped in batches. Through the first article inspection, systemic problems such as severe wear and tear of fixtures or installation and positioning errors, poor accuracy of measuring instruments, misreading of drawings, incorrect feeding or formulas, etc. can be found, and corrective or improvement measures can be taken to prevent batch failures. Goods happen.

The following is an introduction to some common methods of first inspection. According to different production and processing requirements, companies generally choose different testing methods. Although the methods used are different, the final actual effect is the same.

First Article Inspection System

It is a complete integrated system that can directly input the BOM of the produced and processed products into the system. The inspection unit that comes with the system will automatically detect the first sample, and check the input BOM data to confirm the first part of the production and processing. Does the sample plate meet the quality requirements? The system is more convenient and the detection process is automated, which can reduce false detections due to human factors. It can save labor costs, but the initial investment is relatively large. There is a certain market in the current SMT industry. Recognized by certain companies.

LCR measurement

This kind of test method is suitable for some simple PCB circuit boards. The components on the PCB circuit board are reduced, there is no inherited circuit, and there are only some PCB circuit boards with components. After the completion of the printing, there is no need to reheat the PCB circuit. The components on the board are measured and compared with the rated values of the components on the BOM. If there is no abnormality, the formal production and processing can be started. This type of method is widely used by many SMT factories because of its low cost (only one LCR can operate).

3AOI testing, this testing standard is very common in the SMT industry and can be used for all PCB circuit board production. The key is to determine the soldering problems of electronic components through the shape characteristics of the electronic components, and also through the The color and silk screen on the IC are checked to determine whether the electronic components on the PCB circuit board have wrong parts. Most of each SMT production line will be equipped with one or two AOI equipment as standard.

Flying probe detection

This kind of test standard is usually used in some small batch production. Its advantages are convenient testing, strong program variability, and good versatility. Most of them can test all types of PCB circuit boards. However, the inspection efficiency is relatively low, and the inspection time for each board will be very long. This inspection needs to be carried out after the product passes through the reflow furnace. The key is to measure the resistance between two fixed points to determine whether the electronic components in the PCB circuit board have short circuits, empty soldering, and wrong parts.

ICT testing

This inspection method is usually used on models that have been mass-produced, and the amount of production is usually relatively large. The inspection efficiency is high, but the manufacturing cost is relatively large. Each type of PCB circuit board requires a special fixture. The service life of the fixture is not very long, and the inspection cost is relatively high. The principle of detection is similar to that of flying probe detection. It is also by measuring the resistance between two fixed points to determine whether the electronic components on the circuit have short circuits, empty soldering, and wrong parts.

function test

This detection method is usually used on some more complex PCB circuit boards. The PCB circuit board that needs to be tested must be completed after welding, through some specific fixtures, to simulate the formal use of the PCB circuit board, and the PCB circuit board Put it in this kind of simulated scene, and observe whether the PCB circuit board can be used normally after turning on the power. This test standard can accurately determine whether the PCB circuit board is normal. However, there are also the problems of low detection efficiency and high detection costs.

7X-RAY inspection, for some PCB circuit boards with BGA packaged electronic components, X-ray inspection is required for the first product produced. X-ray has strong penetrability and is the first to be used for various types of PCB circuit boards. A kind of instrument for inspection occasions, X-ray perspective can show the thickness, shape and quality of solder joints, and solder density. These specific indicators can fully reflect the welding quality of the solder joints, including open circuits, short circuits, holes, internal bubbles and insufficient tin, and can be quantitatively analyzed.