PCBA Tech - About SMT chip process principle and equipment

The placement machine is one of the main equipment of the SMT production line. The main work is picking and placing (picking ad place), but because the picking speed is very fast, it generally requires at least tens of thousands or even tens of thousands of points per hour; the requirements for picking up objects are very high. Small, generally required as small as one-tenth of a millimeter; Picking accuracy is very high, and generally required to be accurate to tens of microns; Picking success rate is very demanding. At this stage, 4R and 5R are the standards. In the future, 6R or even zero defects may be required. The placement also requires fast, precise, and high-through rate. Based on the above reasons, the device that controls the placement, that is, the placement machine has undergone great changes. The speed is as high as more than 100,000 pieces per hour, and the accuracy is as high as 40Lm or less, and the placement ability can be As small as SI 0201 components and 0.3mm pitch devices, it has become a fact that the through rate can achieve 6R.

Because of the above reasons, it is imminent to control the quality of the patch to find a high-precision patch process. This article explains how to control the quality of the patch from the components selection, placement equipment, environment and other aspects.

2.1 Basic structure of placement equipment

(1) Rack

The common frame has integral casting type and welding type.

(2) Feeder

The feeder system is mainly composed of feeder, loading and transport mechanism.

(3) Mounting head

It is the main part of the placement and reclaiming action of the placement machine. Through the good cooperation between the various structures of the placement head, the picking and placement of components is completed, and the wrong components are thrown into the waste collection box.

(4) PCB positioning device

Before the PCB is loaded into the machine, make sure that the origin position of the PCB is consistent with the machine, so that the correct placement position can be obtained through the transformation of the coordinate system.

(5) Component centering device

Find out the collection size, feature, center, and other data of the component by means of camera visual positioning, etc., to correct the deviation of the component direction and rotation angle through the data of the control system.

(6) Software and system

Generally, each factory has its own programming method. You can write your own software or buy professional offline software, and equipment manufacturers will also bring their own programming software. There are placement machine equipment software that supports DOS, OS/2, APPLE OS, WINDOWS, WINDOWS NT, UNIX and other operating systems.

2.2 Principle of automatic placement

The main task of the placement machine is to pick up the components and mount the components, and program the PCB of the product to be produced by the programmer and according to the performance indicators of the machine to place the correct components in the correct position. The feeder and the PCB board are fixed. The placement head moves between the feeder and the PCB board to pick up the components from the feeder. After adjusting the position and direction of the components, they are then placed on the substrate.

2.2.1 Principles of PCB Reference Calibration

When the automatic placement machine is placed, the placement coordinates of the components are calculated based on a certain vertex angle of the PCB as the origin. However, there are some errors in PCB processing, so the PCB must be calibrated when mounting. The reference calibration is carried out using the reference mark (MARK) and the optical centering system of the placement machine.

2.2.2 Principle of visual alignment

Before mounting, a standard image of each component will be taken and stored in the image library. Each component picked up by Iron Decoration will be photographed and compared with the standard image of the component in the image library. If it is not correct, It will be judged that the model of the component is wrong, and the component will be discarded several times according to the program setting, and then an alarm will be stopped. Or identify the parts with unqualified pin deformation and coplanarity and send them to the throwing position specified by the program. You can also compare the center coordinates and corners of the component after picking up with the standard image, if they are offset. Then automatically correct the placement position according to the offset.

2.3 Work flow of placement machine

(1) Substrate positioning

When the PCB board reaches the stop position through the placement machine track, the camera finds the two identified positions on the PCB board and then calculates the exact position of the placement to ensure the accuracy of the placement to make a smooth, stable and accurate stop.

(2) Component feeding

The components required for placement are provided by the feeder to complete

(3) Pick up components

The placement head picks up components from the feeder

(4) Component positioning

The assembly center of the components is determined mechanically or optically, and the placement position is calculated by the machine to ensure that the coordinate corresponding to the placement position during placement is the central component position of the component to ensure accurate placement.

(5) Mounting

After the placement head picks up the component, the component is accurately and completely placed on the PCB board