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Solder paste printing is a complicated process in SMT patch processing, and it is prone to some shortcomings, which affect the quality of the final product. Therefore, in order to avoid some failures often occur in printing, the common shortcomings of SMT processing solder paste printing can be avoided or solved:
SMT patch
1. Draw the tip. Generally, the solder paste on the pad will be hill-shaped after printing.
Cause: It may be caused by the gap of the squeegee or the viscosity of the solder paste.
Avoidance or solution: SMT chip processing should properly reduce the gap of the scraper or select a solder paste with suitable viscosity.
2. The solder paste is too thin.
The reasons are: 1. The template is too thin; 2. The pressure of the squeegee is too large; 3. The flowability of the solder paste is poor.
Avoidance or solution: choose a template with a suitable thickness; choose a solder paste with a suitable granularity and viscosity; reduce the pressure of the squeegee.
3. After printing, the thickness of the solder paste on the PCB pads varies.
Reasons: 1. The solder paste is not uniformly mixed, which makes the particle size not common. 2. The template is not parallel to the printed board;
Avoidance or solution: Fully mix the solder paste before printing; adjust the relative position of the template and the printed board.
Fourth, the thickness is not the same, there are burrs on the edge and appearance.
Cause: It may be that the viscosity of the solder paste is low, and the hole wall of the template is rough.
Avoidance or solution: Choose a solder paste with a slightly higher viscosity; check the etching quality of the template opening before printing.
Five, fall. After printing, the solder paste sinks to both ends of the pad.
Causes: 1. The pressure of the squeegee is too high; 2. The positioning of the printed board is not firm; 3. The viscosity of the solder paste or the metal content is too low.
Avoidance or solution: adjust the pressure; fix the printed board from the beginning; select the solder paste with suitable viscosity.
6. Incomplete printing means that solder paste is not printed on some parts of the pad.
The reasons are: 1. The opening is blocked or some solder paste sticks to the bottom of the template; 2. The viscosity of the solder paste is too small; 3. There are large-scale metal powder particles in the solder paste; 4. The scraper is worn.
Avoidance or solution: clean the opening and the bottom of the template; select a solder paste with suitable viscosity, and make the solder paste printing can effectively cover the entire printing area; select the solder paste with the metal powder particle size corresponding to the opening size; check and replace the squeegee .
About the common shortcomings of SMT patch processing solder paste printing to avoid or solve methods, today I will introduce it here. Operators understand the causes and solutions of these solder paste printing shortcomings, and can avoid or quickly deal with these problems during work to ensure product quality.
In the daily SMT patch processing work, we most often deal with PCBA processing. Understanding the concept of PCBA processing has become a necessary skill for a high-quality SMT patch processing factory. In this article, we will You introduce PCBA processing and manufacturability design, hope it will be helpful to you.
1. The structure of PCBA
The structure of PCBA has a remarkable feature, that is, the components are mounted on one or both sides of the PCB. In order to facilitate communication, the two sides of PCBA are defined in IPC-SM-782. Usually, we call the side with more mounting components and packaging types as the primary side (Primary Side); on the contrary, the mounting component The surface with fewer package types is called the secondary side (Secondary Side), which respectively correspond to the Top surface and the Bottom surface defined by the EDA layer sequence.
Since the auxiliary assembly surface is usually welded first, and then the main assembly surface, sometimes we also call the auxiliary assembly surface the primary welding surface and the main assembly surface the secondary welding surface.
2. PCBA manufacturability design
The manufacturability design of PCBA mainly solves the problem of assemblability, and aims to achieve the shortest process path, the highest soldering through rate, and the lowest production cost.
The design content mainly includes: process path design, assembly surface component layout design, pad and solder mask design (related to pass-through rate), assembly thermal design, assembly reliability design, etc. The process path is mainly determined according to the total number of components used and the package type, which determines the layout of the components on the PCBA assembly surface.
3. Printed circuit board assembly
Printed circuit board assembly (Print Circuit Board Assembly, abbreviated as PCBA), refers to a printed circuit assembly that is equipped with electronic components and has certain circuit functions. It is also called a single board in an electronic manufacturing plant.
