Development of wave soldering

SMT is the abbreviation of Surface Mount Technology, which translates into surface mount technology. The United States is the invention of SMT. In 1963, the world ’s first surface-mount component appeared and Philips introduced the first surface-mount integrated circuit. SMT has been mainly used in military, aviation, aerospace and other cutting-edge products and investments since its inception Such products are gradually widely used in various industries such as computers, communications, military, industrial automation, and consumer electronics. SMT is developing very rapidly. Into the 1980s, SMT technology has become the most popular new generation of electronic assembly technology in the world, and is known as a revolution in electronic assembly technology. As a "world factory", China currently has no less than 10,000 SMT production lines and is a veritable SMT production country. However, due to the large SMT investment and strong technicality, for many domestic enterprises that are new to this field, how to select and build SMT production equipment in the face of many models is still a complex and

 

Hard work. This article will give a general introduction to SMT equipment for reference when enterprises build SMT lines.

 

1. SMT equipment: the choice of placement machine is the most critical

 

The general SMT production process includes three steps: solder paste printing, placement and reflow soldering. Therefore, to form a complete SMT production line, it must include equipment to implement the above process steps: printing machine, placement machine and reflow furnace. In particular, the placement machine often accounts for more than 60% of the investment in the entire production line, so the selection of the placement machine is the most critical. This article introduces the basic situation of these three devices.

 

1.1 Mounter

 

1.1.1 Classification of placement machine

 

At present, there are many manufacturers producing placement machines with different structures, but they can be roughly divided into large high-speed machines (commonly known as "high-end machines") and medium-sized medium-speed machines (commonly known as "mid-range machines") according to scale and speed. Small placement machines and semi-automatic / manual placement machines will not be introduced in this article. A mainframe is generally three to four times more expensive than a medium-sized one. Manufacturers of large-scale high-speed placement machines are mainly Panasonic, Siemens, Fuji, Universal, Hitachi (formerly Sanyo), etc .; manufacturers of medium-sized medium-speed placement machines are mainly Juki, Yamaha, Samsung, Mirae, Mydata, etc. Among them, Panasonic, Siemens, and Fuji chip mounters have the highest market share, and are known as the "troika" of the chip mounter market.

 

Regardless of the mainframe manufacturer or the medium-sized machine manufacturer, the recommended SMT production line generally consists of 2 placement machines: a chip Chip component placement machine (commonly known as high-speed placement machine) and an IC component placement Machine (commonly known as high-precision placement machine), so that each has its own responsibilities, which is conducive to the highest production efficiency of the SMT production line. But the situation is changing now, because many manufacturers have introduced multi-functional placement machines, making it possible for the SMT production line to consist of only one placement machine. A multi-functional placement machine can complete the placement of all components while maintaining a high placement speed, which reduces investment. This placement machine is favored by small and medium-sized enterprises and research institutes. Typical models are Siemens' F5 series and Panasonic's MSF.

 

1.1.2 placement machine structure

 

At present, the structure of the placement machine can be roughly divided into four types: boom type (also known as "arch type"), composite type, turret type and large parallel system.

 

       (1) Boom type. Boom machine is the most traditional placement machine, has better flexibility and accuracy, is suitable for most components, high-precision machines are generally this type, but its speed cannot be compared with composite, turret and large Compared to parallel systems. However, the component arrangement is increasingly concentrated on active components, such as QFP (Quad flat package) and BGA (Ball grid array). The mounting accuracy is critical to high yield. Role. Composite, turret, and large parallel systems are generally not suitable for this type of component installation. Boom machines are divided into single-arm type and multi-arm type. The single-arm type is the first multi-functional placement machine that is still used today. The multi-arm mounter developed on the basis of the single-arm type can double the working efficiency. For example, the GSM2 mounter of Universal Corporation in the United States has two boom mounting heads, which can alternately , Printed wiring board) for installation. . Most mounter manufacturers have introduced high-precision mounters and medium-speed mounters using this structure, such as Universal's GSM series, Hitachi's TIM-X, Fuji's QP-341E, and XP series BM221 from Panasonic, CP60 series from Samsung, YV series from Yamaha, KE series from Juki, and MPS series from Mirae.

 

(2) Compound type. The compound machine is developed from the boom type machine. It combines the characteristics of the turret type and the boom type. A turntable is installed on the boom. Like the Siplace80S series of Siemens placement machines, there are two with 12 The rotating head of the nozzle is shown in Figure 2. Universal also introduced a rotating head with 30 nozzles, called the "lightning head". Two such rotating heads are mounted on the Genesis placement machine, which can achieve a placement speed of 60,000 pieces per hour. In the strict sense, the compound machine is still a boom type structure. Since the compound machine can increase the speed by increasing the number of booms, it has great flexibility, so its development prospects are promising. For example, the HS60 machine of Siemens has 4 rotating heads, and the placement speed can reach 60,000 pieces per hour. .

 

(3) Turret type. The concept of a turret is to use a set of moving feeders. The turret picks up components from it and then places the components on a circuit board located on a moving workbench. The structure is shown in Figure 3. Since the turret type machine picks up components and mounts at the same time, the placement speed is greatly increased. The high-speed placement machine of this structure is also widely used in China. Not only is it fast, but also the technology has been very mature after more than ten years of development. For example, the CP842E machine of Fuji company can reach 0.068 seconds per piece. However, due to the limitation of the mechanical structure, the placement speed of this machine has reached a limit and it is impossible to increase it significantly. The disadvantage of this model is that it can only handle strips.

 

        Turret machines are mainly used in the production of large-scale computer boards, mobile phones, home appliances and other products. This is because of these products, the resistance-capacitance components are particularly many and the assembly density is high, which is very suitable for this model. produce. Quite a few Taiwan-funded, Hong Kong-funded electronics assembly companies and domestic electrical appliance manufacturers have adopted this model to meet the requirements of high-speed assembly. The main manufacturers of turret machines are Panasonic, Hitachi, and Fuji.

 

(4) Large parallel systems. Massively parallel systems use a series of small individual placement units. Each unit has its own lead screw position system with a camera and placement head. Each placement head can pick up a limited tape feeder, place a part of the PCB, and the PCB advances step by step in the machine at fixed intervals. Individual unit machines run slowly. However, their continuous or parallel operation has high yields. For example, Philips' AX-5 machine can have a maximum of 20 placement heads, achieving a placement speed of 150,000 pieces per hour, which is the industry's first, but for each placement head, the placement speed is Around 7500 tablets per hour, there is still the possibility of a substantial increase. This model is also mainly suitable for large-scale production, such as mobile phones. It should be noted that for various reasons, this model has a much smaller market share in China's electronics industry than the first three models. The major manufacturers of large-scale parallel system machines are Philips, and Fuji has also introduced a NXT-type ultra-high-speed placement machine with a similar structure. By mounting a replaceable placement head, the same machine can be either a high-speed machine or a high-speed machine. It is a general-purpose machine, which can mount almost all placement components, thereby reducing the initial investment in equipment and increasing equipment investment to a minimum.

 

1.1.3 Mounter Comparison

 

Compound, turret and large parallel systems are high-speed installation systems, and are generally used for small chip component installations. A turret machine is also called a "Chip shooter" because it is commonly used to assemble chip resistors. In addition, such machines have the ability to "shot" at high speed. Because passive components, that is, "chips" and other leaded components, are not required to have high accuracy, the shooting machine assembly can achieve higher productivity. Because the structure of high-speed machines is much more complicated than that of ordinary boom-type machines, the price is also much higher. This must be considered when selecting equipment.

 

The test shows that the installation accuracy of the boom type machine is better, and the installation speed is 5000-20000 components per hour. The assembly speed of compound and turret machines is relatively high, generally 20,000-60000 per hour. Large-scale parallel systems have the fastest assembly speed, reaching 50,000-150,000.

 

1.2 Printing press

 

Unlike the placement machine, there are far fewer manufacturers of printing presses, mainly MPM in the United States, DEK in the United Kingdom, Minami in Japan, Hitachi, EKRA in Germany, especially MPM and DEK, regardless of brand awareness or market share It seems that they are all leaders in the printing press market. Printing machines can be divided into two types: semi-automatic and fully automatic. Semi-automatic cannot be connected with other SMT equipment and requires human intervention (such as conveying boards), but the structure is simple and the price is cheap (only equivalent to 1/10 ~ 1 / 5), suitable for scientific research institutes, the typical model of DEK 248. Fully automatic printing machine can be connected to the SMT production line without human intervention. It has a high degree of automation and is suitable for large-scale production. For example, the British DEK company DEK265 INFINITY printing press is a fully automatic printing press with servo pressure control system. The printing parameters can be set digitally by a computer. The screen and substrate marks can be automatically identified and aligned by its vision system. The printing repeat positioning accuracy can reach ± ​​0.004mm and the printing cycle is 8 seconds. Other typical models include the UP3000 series of MPM, the MK series of Minami, and the X5 of EKRA.

 

It should be pointed out that in the traditional solder paste printing process, one of the biggest variables that affect the printing effect is the constantly changing quality of the solder paste placed on the stencil; the evaporation of the flux in the solder paste; the evaporation of the low boiling point solvent in the solder; Oxidation of solder balls in an open environment and poor printability of solder paste during printing pauses. In addition, with the use of solder paste, the amount of solder paste pushed by the doctor blade is reduced, which causes missed printing, or the mesh cannot be completely filled due to excessive solder paste sticking to the doctor blade. The solution to this problem is to place the solder paste in a container and use an automatic solder paste application system to ensure that the solder paste is added to the template in a timely manner. In addition, the use of a container with a coating system reduces the exposure of solder paste to the operator and keeps equipment and other tools as clean as possible. At present, both MPM and DEK companies have adopted this new technology. MPM calls it "rheological pump" and DEK calls it "ProFlow".

 

1.3 Reflow oven

 

Reflow soldering equipment is developing efficiently, multifunctionally and intelligently. Among them are reflow furnaces with unique multi-jet airflow control, reflow furnaces with nitrogen protection, reflow furnaces with local forced cooling, and component temperature monitoring. Reflow ovens, reflow ovens with dual conveyors, reflow ovens with center support, etc. In addition to the above-mentioned new reflow furnaces, intelligent reflow furnaces have also appeared. The adjustment operation is controlled by a built-in computer. In the Windows operating environment, various data can be easily entered using the keyboard or light pen, and can be quickly accessed Take out or replace the reflow soldering process curve in the memory, save adjustment time and improve production efficiency. The operation of many mechanisms of the intelligent reflow furnace, for example: automatic reflow furnace starts and stops, the stored reflow soldering process curve is selected at a specified time, the heating zone settings are automatically adjusted, the reflow furnace is started, and it is closed at that time. The width of the chain conveyor is automatically adjusted to match the size of the printed circuit board. The automatic setting of functions such as the nitrogen pass process and the conventional air reflow process does not need to be manually operated. All are controlled by computer programs. The emergence of intelligent reflow ovens has added new vitality to the SMT soldering process.

 

主要 The main manufacturers of reflow ovens are American BTU, Heller, German ERSA, SEHO, Dutch SOLTEC, and Japanese ANTOM. Reflow ovens can also be manufactured by domestic manufacturers, such as Jintuo, Chuangyi, etc. Although the functionality, stability, and temperature control accuracy are somewhat different from foreign advanced levels, the performance can fully meet the demand and the price is much cheaper.

 

2. Line design: Do not blindly seek for the best

 

建立 When establishing an SMT production line, a reasonable introduction plan should be formulated based on the investment capacity of the enterprise, the size of the output, and the requirements for the placement accuracy of the circuit board. When choosing equipment, you should be “tailored”, and you must not blindly seek for perfection, so as not to cause unnecessary waste.

 

 3. Evaluation: Ensure equipment performance meets requirements

 

购买 When purchasing SMT equipment, it is important to evaluate the equipment in accordance with appropriate standards. The evaluation should focus on the capabilities of all aspects of the equipment to be purchased to ensure that the equipment performance meets the requirements. We take the most critical placement machine evaluation in SMT equipment as an example, the following is a list of evaluation of a certain type of high precision placement machine. There are four aspects: PCB processing, component range, component feeder, and placement requirements.

         (1) PCB processing

 

Description Requirements (example)

PCB size, maximum and minimum 50 × 50mm ~ 460 × 510mm

PCB thickness, maximum and minimum 0.6mm ~ 3.0mm

Mounting area, maximum 458 × 508mm

Positioning method Edge clamping

Positioning accuracy ± 0.05mm

板 Bad Board Identification Requirements

传输 Board transmission edge 3mm

基准 Fiducial camera Grayscale imaging

 

        (2) Component range

 

Description Requirements (example)

Standard Ability Minimum 80

脚 Dense Foot Capability SO-8 ~ PLCC84

GA BGA capabilities 8, 12, 16, 24, 32, 44, 56, 56, 72