I. Introduction

 

 

 

Mounting technology is one of the essential basic technologies in surface assembly technology. It evolved from the English name "Pick and Place" (pick and place), so some materials still call it pick and place technology. The English names of placement technology include "Chip Mounter" (chip component mounting) and "Component Mounter" (component mounting), as well as "ChipPlacement" (chip component placement) and "Component Placement" (component placement), which are different from today's The common Chinese names "mounting technology" or "SMT technology" are more consistent.

 

 

 

1. Features of mounting technology

 

 

 

Placing items or machine parts into specified locations quickly and accurately is a common process or operation process in various manufacturing and assembly in industrial systems. For example, in semiconductor integrated circuit packaging, in semiconductor packaging technology, the manufactured chip is removed from the dicing film and placed in a set position on the lead frame or packaging substrate (substrate) for the next step. Wire bonding or other interconnection processes are called Die Attaching, which is actually a mounting technology. Since in packaging technology, the chip shape and pick-up performance have relatively little change, the chip loading process is not technically critical compared to other complex and precision-requiring processes, and chip loading is usually combined with a bonding machine. A kind of equipment, so in packaging technology, placement is far less important than assembly technology. However, the two mounting technologies, process requirements and equipment principles are essentially the same, except that the chip mounting in packaging technology is higher than that of assembly technology in terms of equipment accuracy and process requirements. In recent years, with the development of high-density and high-precision assembly technology, the boundaries between packaging technology and assembly technology have begun to blur, assembly technology has begun to cross-integrate with packaging technology, and packaging-level precision placement machines have begun to be used in assembly technology. "Mounting" and "Satching" are shown in the figure below.

 

 

 

 

 

As far as the working principles and requirements of the placement technology itself are concerned, it is actually quite simple. Use a certain method to remove the SMC/SMD (surface mount components and surface mount devices) from its packaging and place it on the specified position of the printed board. However, there are few other process requirements in industrial systems that can be compared with the placement technology in SMT. The geometric size and shape, surface properties and weight range of the placement object (SMC/SMD), the requirements for placement speed and placement accuracy are vastly different from their working principles. The diversity of mounted components is shown in the figure below.

 

 

 

 

 

The characteristics of placement technology are described below.

 

 

 

(1) Mounting objects - surface mount components

 

① Types of surface mount components: covering almost all traditional electronic components. Figure 1.9 shows only a part of it.

 

② Volume of surface mount components: Taking chip components as an example, commonly used chip resistors range from 6.14mm3 (3216) to 0.0096mm3 (0402), a difference of about 640 times. If compared to different types, for example, surface mount transformers or connectors, the difference is thousands of times.

 

③ Top material of surface mount components: ceramics, metals, various plastics and other materials with different surface flatness and smoothness.

 

 

 

(2) Mounting speed

 

Since there are at least several to dozens of components on a circuit board, and as many as dozens or hundreds of components, hundreds to thousands of components, and these components can only be mounted one by one, so in order to improve efficiency , the current placement time of each component has been shortened to about 0.06 s (chip components), which has almost reached the limit of the movement speed of the mechanical structure.

 

 

 

(3) Mounting accuracy

 

Due to the continuous increase in assembly density and the application of 0.3/0.4 pitch IC and 0402 components, the requirements for placement accuracy are getting higher and higher. Using integrated mechanical, optical, electrical, and software and hardware technologies, the placement accuracy can now reach 75 μm under 3 Sigma. Some small components and fine pitch IC placement accuracy even requires 50 μm or higher under 4 Sigma. . The distance between components and components and between components reaches the order of 0.1mm, which means that SMT placement accuracy indicators are already on the same level as packaging technology requirements.

 

 

 

 

(4) Mounting the carrier circuit board

 

The main factors related to the mounting technology of the circuit board carrying mounted components are the geometric size and the stiffness in the thickness direction. The area of the circuit board can range from a minimum of less than 1 cm2 to a maximum of more than 4000 cm2, and the thickness dimension, which determines the stiffness of the circuit board in the thickness direction, varies from less than 0.5mm to more than 6mm (rigid board).

 

Since in SMT mounting technology, there are many types, geometric dimensions and parameters that affect mounting from surface mount components to carrier circuit boards, the mounting accuracy has reached the order of nanometers, while the mounting speed is close to the limit of mechanical operation. Therefore, placement technology has very high requirements on equipment. It is no exaggeration to say that placement technology is the key to surface assembly technology, and the placement machine, as a surface mounting equipment, plays a decisive role in placement technology that other technologies cannot match.

 

 

 

2.) Contents of placement technology

 

Mounting technology mainly includes two parts: mounting technology and mounting equipment, as shown below.

 

 

 

 

 

2. Mounting process

 

 

 

Mounting process In terms of mounting methods, there are three process methods: manual method, semi-automatic method and fully automatic method. Although the degree of automation of electronic assembly is getting higher and higher, in R&D departments, laboratories and scientific research institutions, manual and semi-automatic methods still have practical value. Even large-scale assembly factories cannot completely eliminate manual methods at present. In fully automatic Sometimes you can see examples of manual placement on the production line.

 

 

 

No matter which process method is used, the basic process is the same, that is: printed board loading, transportation and alignment, components "appear" at the set pickup position, picking up components, component inspection and positioning alignment Accurately, the components are placed and the printed board is transferred out of the work area.

 

 

 

1) Manual mounting

 

Manual mounting is to use tweezers or a vacuum suction pen to pick up the components from the package and place them at the specified position on the printed circuit board, as shown in the figure below. The manual placement machine used in the early days did not have machine positioning and placement control mechanisms. Although a so-called placement machine was used, it actually still fell into the category of "manual placement". Tweezers are only suitable for chip components, some dual-row leaded integrated circuits, and some special-shaped components. For QFP packaged integrated circuits, a vacuum suction pen must be used, and for some fine-pitch integrated circuits, a magnifying glass must be used. The speed, correctness and accuracy of manual placement completely depend on the operator's technical level and responsibility, so this method is neither reliable nor efficient. For IC packages such as BGA and CSP and chip components below 1005, the manual mounting method is already insufficient, and it is difficult to ensure the placement quality.

 

 

 

 

 

 

 

2) Semi-automatic placement

 

There is no "semi-automatic placement" placement method in the previous SMT materials, and it is indeed rare to see this method in actual production. However, this kind of automatic placement does exist in laboratories and scientific research institutions. and manual placement. The so-called semi-automatic placement method refers to a placement mechanism that uses simple mechanical positioning control, or a placement method that although it has more advanced positioning, detection and placement mechanisms, it cannot form an automatic assembly line function.

 

 

 

Since the semi-automatic placement method has a machine positioning and alignment mechanism, it gets rid of the limitations of manual placement. It not only improves efficiency and reliability, but also can mount various components, even the latest IC packages and chip components, so it is widely used in scientific research work. It plays an indispensable role in the product development and trial production of enterprises. The placement mechanisms newly developed by some companies in response to this demand have high accuracy and component adaptability, and are also high-tech products.

 

 

 

The picture below is a semi-automatic placement equipment used for product development, laboratories and scientific research.

 

 

 

 

 

3) Fully automatic placement

 

Fully automatic placement is an assembly method that uses fully automatic placement equipment to complete all placement processes. It is currently a commonly used placement method in large-scale production. In fully automatic placement, the printed board is loaded, transported and aligned, the components are moved to the set pickup position, the components are picked up, the components are detected and positioned and aligned, and the components are placed until the printed circuit board is printed. The entire process of board making and conveying away from the work area is completed by fully automatic machines without manual intervention. The placement speed and quality mainly depend on the technical performance of the placement equipment and its application and management level.

 

 

 

The fully automatic placement process is the crystallization of the comprehensive application of modern automation, precision and intelligent industrial technology. In the fully automatic placement machine, comprehensive high technologies of modern machine-optical-electricity integration such as precision machinery, high-speed and high-precision visual detection and control, intelligent detection and motion control, and computer numerical control are applied to achieve placement speed and accuracy. The performance, production efficiency and flexibility are continuously improved and perfected.

 

 

 

The fully automatic mounting process is the most equipment-dependent process in surface mounting technology. The production capacity, efficiency and product adaptability of the entire SMT production line mainly depend on the mounting process. In fully automatic mounting, the placement machine equipment play a decisive role. But this does not mean that equipment determines everything. Having advanced equipment does not mean having advanced technology and management, nor does it mean that high efficiency, high quality and high productivity can be naturally achieved. Just like a healthy and energetic person, without corresponding IQ and EQ, it is impossible to achieve career success.

 

 

 

3. The composition of the placement machine and its work flow

 

 

 

1) What is a placement machine?

 

SMT is the current common name for placement equipment in the industry. In the early days, people called placement equipment Pick-and-Place Equipment or Placement Equipment according to the basic functions of placement. Some people also called it Pick-and-Place Equipment. Component mounting machine (Chip Mounter or Component Mounter and Chip Placement and ComponentPlacement). A turret-type high-speed placement machine that was popular in the 1980s and 1990s and was specially used to mount chip components (Chip). The placement speed reached more than 36,000 pieces/h (usually expressed in cph), also known as ChipShooter.

 

 

 

The placement machine is the electronic manufacturing equipment with the largest value, the highest technical content, and the greatest impact on the entire assembly production capacity and efficiency among the entire SMT production equipment. The key to the selection and configuration of the SMT assembly line is the placement machine.

 

 

 

2) Composition of placement machine

 

The placement machine is actually a precision industrial robot that fully utilizes the high-tech achievements of modern precision machinery, electromechanical integration, photoelectric integration, and computer control technology to achieve high-speed, high-precision, and intelligent electronic assembly and manufacturing equipment. According to the assembly technical requirements and the manufacturer's design concept, people have launched patch machines with different functions, different uses, and different grades. But no matter which kind of placement machine, it consists of the following 5 main parts.

 

 

 

(1) Mechanical system

 

• Rack casing: It is the "skeleton" and "skin" of the patcher, supporting all transmission, positioning and transmission mechanisms, and protecting various mechanical and electrical hardware of the machine.

• Transmission mechanism: Its function is to send the PCB to a predetermined position, and then transfer it to the next process after the patch is completed.

• Servo positioning system: Its function is to support the placement head to ensure precise positioning of the placement head; second, to support the PCB carrying platform and enable the PCB to move in the X-Y direction. This system determines the placement accuracy of the machine.

 

(2) Identification and monitoring system

• Identification system: Confirm the placement performance and position of the identification objects (PCB, feeder and components) during the work process.

• Monitoring sensors: The placement machine is equipped with various types of sensors, such as pressure sensors, negative pressure sensors and position sensors. They are like the eyes of the placement machine, monitoring the normal operation of the machine at all times. The more sensors are used, the higher the level of intelligence of the placement machine.

 

(3) SMT head system

The placement head is a key component of the placement machine. After picking up the components, it can automatically correct the position under the control of the correction system and accurately place the components in the designated position.

 

(4) Feeder system

The SMC/SMD is provided to the placement head according to a certain rule and order for accurate picking, so it occupies a large number and position in the placement machine.

 

(5) Computer software and hardware system

It is the control and operating system of the placement machine, directing the placement to run effectively.

 

3) Work flow of the placement machine

The placement machine can quickly and accurately mount SMC/SMD components to the designated solder joints on the PCB according to the assembly process requirements without damaging the components and the printed circuit board through functions such as absorption-displacement-positioning-placement. On the disk position, the basic process is as follows.

① The PCB to be mounted enters the conveyor track. The sensor at the entrance of the track detects the PCB. The system notifies the conveyor belt motor to work and sends the PCB to the next position.

② When the PCB enters the starting point of the work area, the conveyor device sends the PCB to the placement position. When it is about to reach the position, it triggers the sensor of the placement position. The system controls the corresponding mechanism to make the PCB stay at the predetermined placement position. The mechanical positioning device works to fix the PCB in a predetermined position. The clamping device works to clamp and fix the PCB to prevent the PCB from moving.

③ The PCB positioning device works to determine that the position of the PCB is at the predetermined position, otherwise the position coordinates of the PCB are corrected with reference to the system coordinate system.

④ Check the processing optical identification mark points (Mark) according to the program settings to determine the PCB position.

⑤ The components packaged in the special feeder are transported or prepared to the predetermined location according to the programmed location. ⑥ The nozzle of the placement head moves to the position of picking up components, the vacuum is turned on, and the nozzle descends to pick up the components.

⑥ The nozzle of the placement head moves to the position of picking up components, the vacuum is turned on, and the nozzle descends to pick up the components.

⑦ Use the vacuum pressure sensor or photoelectric sensor to detect whether the component is sucked.

⑧ Detect the component height (vertical direction) through a camera or photoelectric sensor.

⑨ Detect the component rotation angle (horizontal direction) through a camera or photoelectric sensor, identify the component characteristics, then read the component characteristic values preset in the component database, compare the actual value with the detected value, and then judge the component characteristics. When the characteristic values do not match, it is judged that the picked component is wrong and the component is picked again. If they match, the current center position and corner of the component will be calculated.

⑩ Throw the wrong components into the scrap collection box.

⑪ According to the program setting, adjust the component angle through the rotation of the placement head; adjust the X/Y coordinates to the position set by the program through the movement of the placement head or the movement of the PCB, so that the center of the component coincides with the placement position point.

⑫ The nozzle drops to the preset height, the vacuum is turned off, the component falls, and placement is completed.

⑬ Start looping from step 5 until placement is completed.

⑭ The patch part moves to the unloading position, and the mounted PCB is transferred to the unloading track. The sensor at the start position of the unloading track is triggered, and the control system notifies the conveyor belt motor to work.Feed the PCB to the next position until it is fed out of the machine.