1. SMT environmental requirements

 

 

 

SMT has certain requirements for the cleanliness, humidity and temperature of the environment. In order to ensure the normal operation of the equipment and assembly quality, the working environment has the following requirements.

 

 

 

1. Power supply

 

 

 

• The power supply voltage and power of the environment must meet the requirements of the equipment. The power of the power supply is usually required to be more than twice the power consumption of the device;

 

• Mainland China’s electricity standards are single-phase AC 220 V (220±10%, 50 Hz) and three-phase AC 380 V (380±10%, 50 Hz). Products sold in mainland China are required to comply with this standard;

 

• Note that the power supply in different regions or in the same region in different seasons may not meet the standards; if the fluctuation of the power supply exceeds the allowable range of the equipment, you must consider configuring a regulated power supply.

 

 

 

2. Environment

 

 

 

(1) Temperature

 

 

 

Since the optimal ambient temperature of the printing studio is 23±3°C, the optimal ambient temperature of the factory is this setting. Usually the factory temperature is generally set at 17~28℃; if it cannot be reached, it cannot exceed the limit temperature of 15~35℃.

 

 

 

(2) Humidity

 

 

 

Humidity in the factory has a great impact on product quality. If the humidity is too high, components will easily absorb moisture, which is detrimental to moisture-sensitive components. At the same time, solder paste will also easily absorb moisture when exposed to humid air, causing welding defects. Too low humidity and dry air can easily generate static electricity, which is detrimental to electrostatically sensitive (ESD) components. Therefore, the humidity in the factory must be controlled. Generally, the relative humidity in the factory is required to be around 45% to 70%RH. Some regulations also specify 30% to 55%RH, and some are more relaxed, reaching 40% to 80%RH.

 

 

 

(3) Air cleanliness

 

 

 

If there is a lot of dust in the workshop, it will have an impact on the placement and welding quality of small components [such as 0201, 01005 and fine-pitch (0.3mm) components]. At the same time, it will increase equipment wear and even equipment failure, increasing the workload of equipment maintenance and repair. . In addition to dust, there are also certain chemical gases in the air in the SMT production workshop. If these chemical gases are toxic and harmful, they will cause harm to the human body; if these gases are corrosive, they will seriously affect the reliability of the product. Therefore, the workspace must be kept clean and sanitary, free of dust, non-corrosive, and free of odorous gases. Ensure product welding quality, normal operation of equipment and human health.

 

 

 

The air cleanliness of the workshop should preferably reach level 100,000 (BGJ73-84). In an air-conditioned environment, there must be a certain amount of fresh air, and try to control the CO2 content below 1000 PPM and the CO content below 10 PPM to ensure human health.

 

 

 

To ensure that the factory's cleanliness reaches level 100,000, a very high cost must be paid, which is difficult for ordinary factories to achieve. In order to ensure such an environment, personnel must pass through the personnel purification room when entering the factory, and there is positive pressure in the entire factory. In an environment of fierce market competition, production profits are getting smaller and smaller. If such requirements are not met, cleanliness must also be stipulated. For example, cartons that affect dust must be clearly stated not to enter the SMT workshop.

 

 

 

A typical case of equipment failure caused by dust: For a certain placement equipment, garbled characters appeared on the screen when it was turned on. At first, it was thought that the operator accidentally changed the machine data or misoperated the software. Then, the battery problem was suspected, because the machine had been running well before. , Later inspection found that there was a lot of dust inside the computer. After cleaning, the machine fault was eliminated.

 

 

 

Case study on the impact of harmful gases in the air on component and product quality: When processing products in a factory, it was discovered that a certain silver-plated component developed serious blackening after being placed in a workshop with a strong smell for 1 to 2 days. , and after being placed in another workshop for 2 days, there was basically no blackening (as shown in Figure 1 below). After analysis, it was found that these black substances are due to substances such as S, N and Cl contained in the air. When these substances adhere to the surface of the component pins, they react with the component surface under appropriate humidity and temperature conditions, generating some oxidation. Substances and salts, as shown in Figure 2 below. The long-term presence of these substances will corrode the surface of components, affect welding, and even affect the reliability of solder joints.

 

 

 

Figure 1 Comparison of blackening on component pins

 

 

 

 

 

Figure 2 Electron microscope and energy spectrum of oxidized black material

 

 

 

3. Factory building

 

 

 

(1) Floor load-bearing

 

 

 

If the equipment is not placed on the first floor, there are certain requirements for the floor load, that is, the floor load must be greater than or equal to 500kgf/m2 before the equipment can be placed, otherwise it will be dangerous.

 

 

 

(2) Anti-static

 

 

 

Since current component production sites must have good anti-static measures, production equipment must be well grounded, and the three-phase five-wire grounding method should be adopted and independently grounded. The floor, workbench mats and seats in the production site should all meet anti-static requirements.

 

 

 

The anti-static method for grounding in some factories is to lay steel plates, which is relatively cheap. The most important anti-static method is anti-static flooring and copper wire covering the entire floor. For anti-static chairs, anti-static chairs can be purchased directly on the workshop production line, but they are more expensive. Office chairs also need to be anti-static, which can be relatively cheaper than those at workstations. A more economical method can also be to purchase ordinary seats, cover them with anti-static covers, and ground the seat legs. A typical anti-static work surface is shown below.

 

 

 

 

 

(3) Exhaust air

 

 

 

Reflow soldering and wave soldering equipment have exhaust requirements to ensure sufficient air suction volume. In addition to the smooth flue, the exhaust air must also have sufficient exhaust air flow, such as 200 m2/h, to ensure that the air is discharged. In addition, a certain static pressure must be maintained, such as 100 Pa, and the diameter of the exhaust pipe also has certain requirements.

 

 

 

(4) Lighting

 

 

 

There should be good lighting conditions in the factory. The ideal illumination is 800 LUX × 1200 LUX, and at least not less than 300 LUX. Wherever there is a visual inspection, lighting requirements must be ensured.

 

 

 

(5) Consideration of vibration of equipment

 

 

 

Vibration will affect the accuracy of precision equipment such as placement machines. At the same time, the vibration of the placement machine will also affect other equipment and buildings. Therefore, there should be certain requirements for environmental vibration, and the impact of the equipment on the environment should be considered. It is best to place the equipment on the first floor, and take certain anti-vibration measures if necessary.

 

 

 

4. SMT production line personnel requirements

 

 

 

Operators of each equipment in the production line must be professionally trained and qualified, and must be proficient in the operating procedures of the equipment. Operators should strictly follow the "Safety Technical Operating Procedures" and "Process Requirements Operation" procedures.

 

 

 

2. Logistics control

 

 

 

When wiring equipment, first consider the flow of logistics. The flow of materials from entering the workshop, printing to welding completion to finished products leaving the warehouse must be smooth. The less time spent staying and turning, the better. Especially for non-connected production models, logistics must be considered more carefully, including whether there is control of semi-finished products, etc. For boards produced on both sides, the logistics direction must be considered.

 

 

 

Logistics is the flow of information, which mainly includes the logistics of materials and indirect materials, as well as the logistics of semi-finished products and finished products. At the same time, pay attention to the importance of inventory. Use IT technology and computer management technology to monitor logistics in real time. Summarize the information connections of each machine. Some machines have network ports and can be connected to the network. You can know the status of the logistics and placement status at any time. At the same time, inventory processing can be carried out, such as output and materials, which is of great help to improve production efficiency. This management technique is of great help to managers. Regarding this knowledge, if the buyer does not ask, the equipment manufacturer will have very little technical support. Buyers tend to pay more attention to the functions of the equipment itself and ignore the control of equipment network management and logistics. For example, for a certain model of machine, to turn on the network protocol, you only need to turn on the option in the software. There is no need to purchase it at an additional price, saving this cost. But if you don't know this, you may have to pay extra.

 

 

 

3. Layout method

 

 

 

1. Production line layout in the factory

 

 

 

(1) Divide areas by customers

 

 

 

In a large factory, certain areas are designated for different customers, and each area only produces products for fixed customers. In this way, when different customers visit, they only visit the corresponding areas and equipment. Because there is no unified standard for the configuration of production lines according to regional divisions, different specific production lines are designed according to the specific products of customers, so the length of the production lines is different, and the equipment configuration is also different. Such a layout requires all customers to have stable processing output and ensure continuous production operation. Otherwise, the production line will be vacant and resources will be wasted. At the same time, due to the different configurations of the production lines and the large variety of machines, it causes difficulties in repair, maintenance and upkeep, and increases the number of repair/maintenance personnel and increases the cost. For example, the layout of a production line divided by customer area is shown in the figure below.

 

 

 

 

 

(2) Layout with the same configuration and layout

 

 

 

All production lines have the same configuration and layout, and there are large intervals between lines. If bottlenecks occur, equipment can be supplemented. The advantage of the layout is that equipment repair and maintenance are simple, and there are fewer repair/maintenance engineering personnel. It is also possible to divide product production areas for different customers. The disadvantage of the layout is: since different customers have different products, the fixed production line may not be suitable for the production of all products, and the production line loss is large. This layout is often used for large line layouts, and the schematic diagram is shown in the figure below.

 

 

 

 

 

(3) Changing production lines

 

 

 

Because the market changes too fast and products change every year, the initially determined production line may not necessarily be the optimal configuration for new products as the product changes. Therefore, it is necessary to change the configuration of the lines in the factory to optimize the efficiency of each production line. If the product is revised, the number of components on the board will hardly change, which is of great benefit to production. The production line can produce new products with little need for adjustment. That is to say, a board with a good product DFM does not require much change in the wire body. For boards with poor DFM, the production line needs to be changed and adjusted to achieve optimal production efficiency. For example, the first version of a product is called version A and has 500 components, including 50 components on the A side and 450 components on the B side. Most of the components are small components and there are no complex QFP or BGA. According to the production cycle design of this product One production line, 2 high speeds and one reflow oven are enough. A year later, it was replaced with the new version B. The number of components attached increased and the complexity increased. There were 800 components, 200 components on side A and 500 components on side B. There was also a CSP0.5 pitch. At this time, a multi-function machine had to be added to meet the requirements. production line requirements.

 

 

 

For production lines that are frequently changed, the configuration of the power supply and gas circuit must be convenient for replacement. For example, there are gas sources and power interfaces at any time and anywhere on the top of the factory building. At the same time, the logistics of such a configuration will be more chaotic than the layout of the same configuration and layout, so careful consideration must be taken. Since the customer's products are not completely fixed, there are many production varieties, there is no unified standard for the configuration of the production line, the length of the line body is different, and there are many types of machines, which causes difficulties in repair, maintenance and upkeep, the number of repair/maintenance personnel increases, and the cost increases. In addition, frequent replacement of production lines will also put pressure on equipment maintenance and maintenance personnel. Equipment engineers often make replacements while others are on vacation.

 

 

 

2. Production line configuration case

 

 

 

(1) EMS small production line configuration

 

 

 

Most EMS companies respond to a flexible approach of small batches and multiple varieties. Corresponding to this model, its typical production line is shown in the figure below.

 

 

 

 

 

Its advantage is that the reflow furnace is connected to the visual inspection, and there is no buffer station in the middle. The visual inspection is performed after passing through the furnace, saving equipment and time. And there is no need to count the quantities in the middle, directly from input to output. The same production line is equipped with personnel from different departments so that each can perform their duties so that quality can receive timely feedback. Most EMS factories use this method to build lines.

 

 

 

(2) Production lines that improve production efficiency and save space

 

 

 

The production of certain products, such as mobile phones, has a small panel area. In order to improve the utilization rate of the equipment, a dual-track production line can be used, as shown in the figure below.

 

 

 

 

 

 

 

The production line mounts both sides A and B of the board at the same time. After the flipping of side A placement is completed, the board is sent to the printing end through the viaduct, side B is printed, and then side B is mounted. All machines use double tracks. Its advantage is that the function of the reflow oven can be fully utilized, and it can save space, personnel and costs.

 

 

 

(3) Large-scale long-line production configuration

 

 

 

If the production scale is relatively large and the products are single and infrequently replaced, the production line configuration is as shown in the figure below.

 

 

 

 

 

This kind of production line is 120 to 130 meters long and is suitable for large-scale production such as 100,000 to 200,000 units. The line body does not frequently switch products. If the line is changed, it will take about 6 hours. This kind of line body was used more in the early days, but is rarely used now, because there are very few products on the market with single-machine sales of 100,000 to 200,000 units, and it is inconvenient to switch models and it takes a long time to change the line.

 

 

 

4. Production line balance optimization

 

 

 

The cost of SMT production line equipment is the main part of the entire production cost. Whether SMT production line equipment can be effectively used to maximize the efficiency of the equipment directly affects the company's efficiency and competitiveness. Therefore, production line balance optimization is an issue that every factory must consider. In the SMT production line, the largest proportion of funds is the placement machine, so the optimization of the production line is mainly the optimization of the placement machine, so that the placement speed of the placement machine can reach or be close to the theoretical value as much as possible, and make the entire line line maximum capacity.

 

 

 

SMT production model and production line optimization can be classified into the following 4 aspects:

 

First, single-machine optimization, that is, the production of one product relative to one production equipment, is called the 1-1 problem;

 

Second, line balance, that is, one product versus multiple production equipment, is called a 1-M problem. The optimization at this time is to balance the workload of the entire production line;

 

Third, product grouping optimization, multiple products relative to one production equipment, is an M-1 problem;

 

Fourth, production plan optimization, multiple products versus multiple production equipment, is an M-M problem. They are introduced below.

 

 

 

1. Single machine optimization

 

 

 

As we all know, there is a certain difference between the theoretical speed of the placement machine and the actual speed, because the theoretical speed of the machine is obtained under certain conditions. For example, the theoretical speed of the Global HSP4796L turret machine is 10 pieces/s; to achieve this The speed must meet 3 conditions:

 

First, the feeder moves no more than 1 material station position;

 

Second, the rotation speed (beat) of the machine placement head is 0.1s/chip;

 

Third, the moving distance of the X-Y table is less than 25mm.

 

In actual production, it is impossible to fully meet these three requirements. For example, the moving distance of the workbench is determined by the position of the mounted components, and the actual mounting speed is lower than the theoretical speed. In order to be as close to the theoretical value as possible, various factors of the placement machine need to be comprehensively considered, such as the location of the component material station, the movement of the placement head, the placement sequence and path, etc., that is, a single placement machine needs to be optimized.

 

 

 

The single-machine optimization of a product relative to the production of a production equipment mainly focuses on optimizing the location of the component material station and the placement path and sequence of the placement machine. To complete placement in the shortest time, you must fully understand the characteristics of the placement machine, including release capability, placement strength, placement accuracy, placement speed, accuracy of positioning axes X, Y and θ, and rotation of the placement head. axis and Z axis, as well as auxiliary various mathematical model simulation technologies, can truly optimize equipment capabilities and improve efficiency. Usually a certain amount of