Electronic Design - What is the role of PCB AOI equipment in PCB design?

The full name of PCB AOI is Automatic Optic Inspection, which is based on the principle of optical vision to detect common defects encountered in PCB soldering production.

Why use PCB AOI?

--In order to carry out quality control, an effective inspection must be carried out on the SMT production line.

The full name of AOI (Automatic Optic Inspection) is automatic optical inspection. Its main purpose is to detect common defects encountered in welding production. It is an equipment based on optical principles. AOI is a new type of test technology that has only emerged in recent years, but its development momentum is very fierce. At present, many manufacturers have introduced AOI test equipment. During automatic inspection, the machine automatically scans the PCB through the camera, collects images, compares the tested solder joints with the qualified parameters in the database, after image processing, checks out the defects on the PCB, and displays/marks the defects through the display or automatic signs Come out and be repaired by maintenance personnel.

The implementation of AOI has the following two main objectives:

(1) End quality

Monitor the final state of the product when it leaves the production line. When the production problem is very clear, the product mix is high, quantity and speed are the key factors, this goal is preferred. AOI is usually placed at the end of the production line. In this position, the equipment can generate a wide range of process control information.

(2) Process tracking

Use inspection equipment to monitor the production process. It typically includes detailed defect classification and component placement offset information. When product reliability is important, low-mix high-volume manufacturing, and stable component supply, manufacturers prioritize this goal. This often requires the inspection equipment to be placed in several locations on the production line, to monitor the specific production status online, and to provide the necessary basis for the adjustment of the production process.

Although AOI can be used in multiple locations on the production line, and each location can detect special defects, the AOI inspection equipment should be placed in a location that can identify and correct the most defects as soon as possible.

There are three main inspection locations:

(1) After solder paste printing

If the solder paste printing process meets the requirements, the number of defects found by ICT can be greatly reduced. Typical printing defects include the following:

A. Insufficient solder on the pad.

B. Too much solder on the pad.

C. Poor registration of solder to pad.

D. Solder bridge between pads.

In ICT, the probability of defects relative to these situations is directly proportional to the severity of the situation. Slightly small amounts of tin rarely cause defects, while severe cases, such as no tin at all, almost always cause defects in ICT. Insufficient solder may be a cause of missing components or open solder joints. Nevertheless, deciding where to place the AOI needs to recognize that component loss may occur due to other reasons, and these reasons must be included in the inspection plan. Inspection of this location most directly supports process tracking and characterization. The quantitative process control data at this stage includes printing offset and solder volume information, and qualitative information about printed solder is also generated.

(2) Before reflow soldering

Inspection is done after the components are placed in the solder paste on the board and before the PCB board is sent to the reflow oven. This is a typical location for inspection machines because most defects from solder paste printing and machine placement can be found here. The quantitative process control information generated at this location provides information on the calibration of high-speed chip machines and fine-pitch component placement equipment. This information can be used to modify component placement or to indicate that the placement machine needs calibration. The inspection at this location satisfies the goal of process tracking.

(3) After reflow soldering

Inspect at the last step of the SMT process. This is currently the most popular choice for PCB AOI because all assembly errors can be found at this location. The post-reflow inspection provides a high degree of security because it identifies errors caused by solder paste printing, component placement, and reflow processes.

Everyone in the PCB industry knows that AOI equipment is an optical inspection device, which usually has the same size and weight as other equipment in the industry. If the AOI equipment is placed in the workshop together with other SMT equipment, the AOI equipment will not look special visually. Readers must have discovered that if we continue to express this, the next step should be that AOI equipment is just like real SMT industry equipment, which is unavoidably sad.

The same is true of the facts. AOI inspection equipment, as an appearance process quality inspection equipment born out of the needs of the SMT industry, is dispensable for some SMT companies. When will it be and when will it be absent? Under analysis, I think there are the following situations:

1. Customers do not have high-quality requirements, but nothing; on the contrary, even if you don’t use it, you must place a decorative quality;

2. PCB components larger than 0402 sizes, but none; generally manual detection below 0402 is very difficult, and AOI testing equipment is needed to improve efficiency;

3, the efficiency requirements are not high, but nothing; on the contrary, if one person replaces the work of three people to improve efficiency, AOI equipment will be the best choice;

4. Small-scale development is optional; small-scale state, small quantity, and few products to be tested. The purchase of AOI equipment is somewhat overkilled;

5. Non-intelligent semi-automated operation is optional; here mainly refers to large and medium-sized SMT companies, because such companies have large orders, more products to be tested, and high-quality requirements. Manual testing is far from efficient and effective. Far from meeting the requirements. Coupled with the continuous intelligentization of SMT equipment, unmanned factories have become the future trend, and AOI equipment is a guarantee for the quality of products produced by unmanned factories.

To sum up, the PCB industry has a development process, which is artificial-mechanization-semi-intelligence-intelligence-unmanned. At present, it is in the semi-intelligence and intelligence interval. The use of AOI equipment in the industry is also at a state of the half, and it has not been fully popularized. Therefore, in the view of some small and medium-sized enterprises, the purchase of AOI is not necessary. This is a very realistic current state, and it also reflects the fact that the status of AOI equipment is not high.