PCBA Tech - Quickly understand the production process of PCBA

1. PCBA production environment

1. General environmental management and control:

Temperature: 20 degree Celsius～26 degree Celsius Relative humidity: 45%～70%

2. Small environment ESD control:

1) Requirements for warehouses and workshops: laying anti-static materials on the ground, laying anti-static rubber on the console, and connecting electrostatic grounding buckles (1MΩ±10%);

2) Employee requirements: wear anti-static clothes, shoes, and hats when entering the workshop, and wear static rings and anti-static gloves when contacting products;

3) Turnover boxes, packaging foams, and bubble bags must meet ESD requirements;

4) The leakage voltage of the equipment is less than 0.5V, the impedance to ground is less than 6Ω, and the impedance of the soldering iron to ground is less than 20Ω. The equipment needs to evaluate the external independent grounding wire.

2. Material control requirements

1. Material requirements:

(1) The PCB storage period is more than 3 months, and it needs to be baked at 120 degree Celsius, 2H～4H.

(2) BGA and IC pin packaging materials are susceptible to moisture and are prone to abnormal reflow soldering quality, so they need to be baked in advance.

(3) Check the humidity card: the displayed value should be less than 20% (blue), if> 30% (red), it means that the IC has absorbed moisture.

2. Requirements for accessories:

Commonly used 63/37 Sn-Pb solder paste. The solder paste must be stored in a refrigerator at a temperature of 2°C to 8°C. Before use, the temperature should be ensured for 4 to 8 hours, and in principle, no more than 48 hours.

Third, the characteristics of SMT process technology

1. SMT, the full name is Surface Mounting Technology, and the Chinese is surface mount technology. It is the direct assembly of SMD parts on the PCB. The advantage is that it has a very high wiring density, and shortens the connection line to improve the electrical performance. Its simple production process is boarding - printing - patching - reflow soldering - AOI inspection - receiving board

2. The SMT placement process is divided into single-sided, double-sided, and mixed processes

4. Introduction to the practical process of SMT production

1. Printing solder paste

The solder paste is uniformly printed on the pads of the PCB to prepare for the soldering of the components, so as to ensure a good electrical connection when the patch components and the corresponding pads of the PCB are reflow soldered. The equipment used is a printing machine. Located at the forefront of the SMT production line.

First make the stencil: the stencil is the stencil of the solder paste. Brush a layer of the solder paste on the stencil, and evenly coat the tin on each pad under the action of a squeegee.

Critical control point: steel mesh opening requirements, in order to achieve 50% hole filling, it should be determined according to factors such as PCB thickness, steel mesh thickness, hole and lead gap, etc. The steel mesh opening must be expanded outside, as long as the outside expansion does not exceed 2mm, the solder paste will be pulled back and filled into the hole.

2. Patch

Mounter: "Surface Mount System". In the production line, it is located behind the printing machine in the SMT production line. It accurately mounts the chip components to the printed tin by moving the placement head A device for the corresponding position of the paste or patch glue on the PCB surface.