What should be noted when selecting a surface mount machine? With the rapid development of surface mount technology, the application of surface mount machines in China's electronic assembly industry is becoming increasingly widespread. Faced with numerous models of surface mount machines, selecting the right one is still a complex and difficult task. When selecting a surface mount machine, several key technical issues should be noted.

Surface mount machine type

At present, surface mount machines can be roughly divided into four types: boom type, composite type, turntable type, and large parallel system. Different types of surface mount machines have their own advantages and disadvantages, usually depending on the requirements of the application or process for the system, and there is also a certain balance between their speed and accuracy.

Mobile arm machines have excellent flexibility and accuracy, suitable for most components. High precision machines are generally of this type, but their speed cannot be compared to composite, rotary, and large parallel systems. However, the arrangement of components is increasingly concentrated on active components, such as QFP and BGA array components with leads, and installation accuracy plays a crucial role in high yield. Composite, rotary, and large parallel systems are generally not suitable for the installation of this type of component. Mobile arm machines are divided into single arm and multi arm types. The single arm type is the earliest developed and still used multifunctional surface mount machine. The multi arm surface mount machine developed on the basis of single arm can double the work efficiency. For example, YAMAHA's YV112 contains two boom mounting heads with 12 suction nozzles, which can simultaneously install two circuit boards.

The hybrid machine is developed from the boom type machine, which combines the characteristics of turntable and boom type. A turntable is installed on the boom, like Siemens' Siplace80S series surface mount machine, which has two turntables with 12 suction nozzles. Due to the flexibility of increasing the number of boom arms to improve speed, the development prospects of hybrid machines are promising. For example, Siemens' latest HS50 machine is equipped with four such rotating heads, with a mounting speed of up to 50000 pieces per hour.

Due to the simultaneous picking up of components and surface mounting actions, the turntable type machine greatly improves the surface mounting speed. This type of high-speed surface mounting machine is most commonly used in China, with not only high speed but also very stable performance. For example, Panasonic's MSH3 machine can achieve a mounting speed of 0.075 seconds per piece. However, due to the limitations of its mechanical structure, the mounting speed of this machine has reached a limit and cannot be significantly increased.

A large parallel system consists of a series of small independent assembly machines. Each has a screw positioning system robotic arm, which is equipped with a camera and mounting head. Each installation head picks up components from several belt feeders and is capable of installing multiple circuit boards in multiple partitions. These boards are aligned in position through machine timed angle changes. For example, PHILIPS' FCM machine has 16 mounting heads, achieving a mounting speed of 0.0375 seconds per piece. However, for each mounting head, the mounting speed is around 0.6 seconds per piece, which still has the potential for significant improvement.

Composite, rotary, and large parallel systems belong to high-speed installation systems and are generally used for the installation of small sheet-like components. Rotary machines are also known as "chip shooters" because they are typically used to assemble chip resistors and capacitors. In addition, secondary machines have the ability to shoot at high speeds. Due to the low precision required for passive components, such as "chips" and other lead components, the assembly of film makers can achieve high production capacity. High speed machines are much more complex in structure than ordinary boom type machines, so their prices are also much higher. When choosing equipment, this should be taken into consideration. The experiment shows that the installation accuracy of the boom type machine is good, with an installation speed of 5000-20000 components per hour (cph). The assembly speed of composite and rotary machines is relatively high, generally ranging from 200000 to 50000 pieces per hour. The assembly speed of large parallel systems is the fastest, reaching 50000-100000 units per hour.

vision system 

The machine vision system is the second factor that significantly affects component installation. Machines need to know the accurate position of the circuit board and determine the position of the components and board to ensure the accuracy of automatic assembly.

Imaging is accomplished through the use of a video system. Video systems are generally divided into overhead, overhead, head or laser alignment, depending on the position or type of camera.

(1) The overhead camera searches for a target (referred to as a reference) on the circuit board in order to place the circuit board in the correct position before assembly;

(2) Looking up cameras are used to detect components at fixed positions, usually using CCD technology. Before installation, the components must be moved above the camera for image processing. At first glance, it seems a bit time-consuming. However, since the installation head must be moved to the feeder to collect the components, if the camera is arranged between the picking position (from the feeding point) and the installation position (on the board), the acquisition and processing of the video can be carried out simultaneously during the movement of the installation head, thereby shortening the installation time;

(3) The head camera is directly installed on the sticker head, usually using Line sensor technology to complete the detection of the components during the process of picking them up and moving them to the designated position. This technology is also known as? quot; Flight centering technology "can significantly improve the efficiency of mounting;

(4) Laser alignment refers to the process of generating a moderate beam of light from a light source and shining it onto a component to measure the impact of the component's projection. This method can measure the size, shape, and deviation of the central axis of the suction nozzle of the component. But for components with pins, such as SOIC, QFPHE, and BGA, a 3D camera is required for inspection. In this way, the alignment of each component requires an additional few seconds of time. Obviously, this will have a significant impact on the speed of the entire SMT machine system. Among the three component alignment methods (CCD, line sensor, laser), CCD technology is the best, and the current CCD hardware performance has a considerable level. In terms of CCD hardware development, we have recently developed "Back Lighting" and "Reflection"; Front lighting technology and programmable lighting control to better meet the needs of various component mounting.

Delivery of materials

The boom type machine can support various types of feeders, such as belt type, disc type, bulk type, tube type, etc. This is in stark contrast to high-speed installation systems, which can only use either bulk or belt feeders. When installing many large ICs such as QFP and BGA, a boom type machine is the only option. In addition to mounting accuracy, the lack of support for disc feeders in high-speed machines is also an important reason.

Generally speaking, manufacturers should consider the universality of feeders on their machines, but sometimes manufacturers may also design feeders for specific machines, which limits their use on other machines. Specialized machines not only result in a large number of feeders being idle, but also require space to store them.

flexibility

Due to the increasingly fierce competition in electronic products and the increasing uncertainty in production, it is necessary to frequently adjust product output or arrange product transformation. Therefore, corresponding requirements have been put forward for surface mount machines, which require good flexibility to adapt to the ever-changing production and manufacturing environment. This is what we commonly refer to as Flexible Manufacturing Systems (FMS). For example, the SMT machine from Global Instruments in the United States only needs to exchange the dispensing components with the SMT components when exchanging functions from dispensing to SMT. This equipment is suitable for multitasking, multi-purpose, and short production cycle processing enterprises. Machine flexibility is a shutdown factor that we need to consider when selecting equipment.