With the rapid development of surface mount technology, placement machines are increasingly used in China's electronic assembly industry. Faced with numerous models of placement machines , how to select one is still a complex and difficult task. This article will give an overview of several key technical issues that should be paid attention to when selecting placement machines , so as to provide reference for enterprises when purchasing equipment.

SMT type

Fully automatic placement machine

At present, placement machines can be roughly divided into four types: boom type, composite type, turntable type and large parallel system. Different types of placement machines have their own advantages and disadvantages, which usually depend on the system requirements of the application or process. There is also a certain balance between their speed and accuracy. At present, the better brands of placement machines are: Siemens placement machines , Fuji placement machines and other placement machines .

 Fully automatic placement machine

Boom-type machines have good flexibility and precision and are suitable for most components. High-precision machines are generally of this type, but their speed cannot be compared with compound, turntable and large parallel systems. However, component arrangement is increasingly concentrated on active components, such as leaded QFP and BGA array components, and mounting accuracy plays a crucial role in high yields. Compound, turntable, and large parallel systems are generally not suitable for this type of component installation. Boom-type machines are divided into single-arm type and multi-arm type. The single-arm type is the earliest developed and still used multi-functional placement machine . The multi-arm placement machine developed on the basis of the single-arm type can double the work efficiency.

 Fully automatic placement machine

The compound machine is developed from the boom-type machine. It combines the characteristics of the turntable type and the boom-type. A turntable is installed on the boom. Like Simens' Siplace80S series placement machine , there are two with 12 suction Mouth turntable. Since the composite machine can increase the speed by increasing the number of booms and has greater flexibility, its development prospects are promising. For example, the latest HS50 machine launched by Simens is equipped with 4 such rotating heads, with a placement speed of up to 50,000 pieces per hour.

Because the pick-up and placement actions of the turntable machine are carried out at the same time, the placement speed is greatly increased. High-speed placement machines with this structure are the most commonly used in our country. Not only are they high-speed, but their performance is very stable. For example, Panasonic The MSH3 machine placement speed can reach 0.075 seconds/piece. However, due to the limitations of its mechanical structure, the placement speed of this machine has reached a limit and cannot be significantly improved.

Large parallel systems consist of a series of small independent assembly machines. Each has a lead screw positioning system manipulator with a camera and mounting head. Each mounting head picks up components from several tape feeders and can mount multiple partitions of multiple circuit boards, which are angularly aligned via machine timing. For example, PHLIPS' FCM machine has 16 mounting heads and achieves a placement speed of 0.0375S/piece. However, for each mounting head, the placement speed is around 0.6S/piece, and there is still the possibility of substantial improvement.

Composite, turntable and large parallel systems are high-speed installation systems and are generally used for the installation of small chip components. The turntable machine is also called a "chip shooter" because it is often used to assemble chip resistors and capacitors. Additionally, such machines have the ability to "shoot" at high speeds. Because the precision required for passive components, known as "chips" and other leaded components, is not high, die-shooting machine assembly can achieve higher throughput. Because the structure of high-speed machines is much more complex than that of ordinary boom machines, their prices are also much higher. This should be taken into consideration when selecting equipment.

Tests have shown that boom-type machines have better installation accuracy and installation speeds of 5,000-20,000 components per hour (cph). The assembly speed of compound and turntable machines is relatively high, generally 20,000-50,000 pieces per hour. Large parallel systems have the fastest assembly speed, up to 50,000-100,000 units.

visual system

The machine vision system is the second factor that significantly affects component installation. The machine needs to know the exact position of the circuit board and determine the relative position of the component and the board to ensure the accuracy of automatic assembly.

Imaging is accomplished using a vision system. Vision systems are generally classified as top-view, upward-view, head- or laser-aligned, depending on the location or type of camera. (1) A top-view camera searches for a target (called a datum) on the circuit board to place the circuit board in the correct position before assembly; (2) A top-view camera is used to detect components at a fixed position, generally using CCD technology , before installation, the component must be moved over the camera for video processing. At first glance, it seems a bit time-consuming. However, since the mounting head must move to the feeder to collect elements, if the camera is installed between the pickup position (from the feed) and the mounting position (on the board), the acquisition and processing of the video can be performed during the movement of the mounting head. At the same time, the placement time is shortened; (3) The head camera is directly installed on the placement head, and line-sensor technology is generally used to complete the detection of components during the process of picking up the components and moving them to the designated position. This kind of The technology is also called "flying alignment technology", which can greatly improve placement efficiency; (4) Laser alignment refers to generating a moderate beam from a light source and shining it on the component to measure the impact of component projection. This method can measure the size and shape of components as well as deviations from the central axis of the nozzle. However, for components with pins, such as SOIC, QFP and BGA, a third-dimensional camera is required for detection. This adds several seconds to the alignment of each component. Obviously, this will have a great impact on the speed of the entire placement machine system. Among the three component alignment methods (CCD, line-sensor, laser), CCD technology is better, and the current CCD hardware performance is at a comparable level. In terms of CCD hardware development, "Back-Lighting" and "Front-Lighting" technologies, as well as programmable lighting control, were recently developed to better cope with various component mounting needs.

Feeding

Boom-type machines can support many different types of feeders, such as belt, tray, bulk, tube, etc. This is in sharp contrast to high-speed installation systems, which can only use bulk or belt feeders.

When installing many large ICs, such as QFP and BGA, boom machines are the best choice. In addition to placement accuracy, the high-speed machine does not support the tray feeder is also an important reason.

Generally speaking, manufacturers should consider feeders for general use on their machines, but sometimes manufacturers will design feeders for a specific machine, which limits the use of the feeder on other machines. Not only do specialized machines leave a large number of feeders sitting idle, they also require space to store them.

flexibility

Due to the increasingly fierce competition in electronic products and the increasing uncertainties in production, it is necessary to frequently adjust product output or arrange product transformation. Therefore, corresponding requirements are put forward for the placement machine , that is, good flexibility is required to To adapt to the current ever-changing production and manufacturing environment, this is what we often call a flexible manufacturing system (FMS). For example, the American Global SMT machine , when exchanging functions from dispensing to SMT, only needs to interchange the dispensing component and the SMT component. This kind of equipment is suitable for processing enterprises with multi-tasks, multi-purposes and short production cycles. Machine flexibility is a key factor to consider when purchasing equipment.

make a choice

Automation equipment is the basis for realizing electronic assembly. When selecting equipment, you must consider the following key issues: machine type, imaging, feeding, and flexibility. With this understanding, you can identify the advantages and disadvantages of different equipment and make a wise choice. At the same time, the selection of equipment should be "tailor-made" and must not blindly seek perfection to avoid unnecessary waste.