PCBA Tech - SMT production line process composition and explanation

SMT, the full name of Surface Mounting Technology, is surface mount technology in Chinese. Various types of electronic components are mounted on the PCB light board. After soldering, subsequent DIP, test and inspection functions, it becomes the final product ---PCBA.

Let me introduce you to the SMT production line process and related equipment, as well as the functions and functions of each equipment, so that everyone has a preliminary understanding of SMT.

1. Programming and debugging the placement machine

According to the sample BOM patch location map provided by the customer, program the coordinates of the PCB pad location where the patch electronic components are located. The purpose of the programming program is to let the placement machine know which pads should be attached to which electronic component, and then compare the first piece with the SMT placement processing data provided by the customer, and then proceed to follow-up production after confirming that it is correct.

2. Printing solder paste

The solder paste is printed on the PCB board where the components need to be soldered with a stencil. The main purpose of the solder paste is to stick the electronic components to the position of the PCB pad. The solder paste is similar to toothpaste, and the main components are tin powder and Flux, to prepare for the soldering of components. The equipment used is a solder paste printer.

3. SPI

The solder paste detector detects whether the solder paste printing is a good product, whether there is any undesirable phenomena such as little tin, leakage, and excessive tin. It is taken by the camera, and then presented on the computer, and then through the system algorithm to determine whether the result is bad.

4. Mounter

The electronic components are accurately installed on the fixed position of the PCB. The placement machine is divided into a high-speed machine and a general-purpose machine

High-speed machine: used for attaching large and small components with pin spacing; general-purpose machine: attaching small pin spacing (pin dense), large-volume components (commonly known as large materials, special-shaped parts, etc., such as shielding covers, connectors), Components with different rules, etc.).

5. Reflow soldering

The main purpose is to melt the solder paste at high temperature, and after cooling, make the electronic components and the PCB board firmly soldered together. The equipment used is a reflow oven. Generally, reflow soldering is divided into ordinary, nitrogen and vacuum reflow soldering. There are mainly four temperature zones, namely Preheating zone, constant temperature zone, welding zone, cooling zone. The furnace temperature curve for reflow soldering must be set reasonably.

6. AOI

Automatic optical detector, to detect whether the welded components have poor welding, such as tombstone, displacement, empty welding, connecting bridge, etc.

7. Manual visual inspection

Manual visual inspection is mainly to detect PCBA false alarms by AOI, because AOI cannot fully detect all welding defects accurately at present, and false alarms will occur due to various situations, that is, a board that is normally welded is falsely reported as a welding problem. Need to use manual visual inspection to re-inspect. Determine whether the board is really bad.

8. Packaging

Qualified products will be packaged separately. The generally used packaging materials are anti-static bubble bags, electrostatic cotton, and blister trays. There are two main packaging methods. One is to use anti-static bubble bags or static cotton into rolls and separate packaging, which is currently the most commonly used packaging method; the other is to customize the blister tray according to the size of PCBA. Place the package in a blister tray, mainly for PCBA boards that are sensitive to needles and have vulnerable SMD components.

Summarize

SMT is one of the most popular electronic product assembly methods. SMT equipment has experienced manual to semi-automatic to fully automatic, and the accuracy has been improved from the previous millimeter level to the current micron level. SMT components have gradually developed in the direction of lighter, thinner, shorter and smaller.