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Technical Article

How To Solve Missing Paste Printing and Less Tin in SMT Assembly?

Time:2021-03-11 11:55:59 Click:

Causes of SMT Assembly missing paste printing and less tin 







1. The principle of solder paste printing


The solder paste is squeezed into the stencil through a scraper so that the solder paste contacts and adheres to the PCB surface. Then the solder paste that adheres to the PCB surface during demolding overcomes the resistance of the stencil wall and is transferred to the PCB surface.



2. Observe, think & compare


A>Although part of the substrate around the pad is covered by the stencil opening during printing, the solder paste at the bottom of the stencil opening is still difficult to contact the PCB pad and the surrounding substrate. As a result, it is not enough to overcome the hole wall during demolding. Resistance (Eg. Only a small amount of solder paste on the pad)?


B>There is a 35 um deep annular pit between the pad and the solder mask. Does the solder paste with the stencil opening on the pit not touch the bottom of the pit?


C>Why are other pads connected to the circuit not easy to miss?



3. Bare copper plate printing verification


The solder paste of 5 different brands of 4# powder can be stably tinned (laser + electro-polished stencil ) on a circular hole with a thickness of 0.1 and an opening diameter of 0.28.







Solutions of SMT Assembly missing paste printing and less tin


1. Find all the pads that are not connected to the outer circuit, change the size of these pads from the original circle with a diameter of 0.27 to a circle with a diameter of 0.31; Also, reduce the area of the deep pit around the pad, and make the original opening area on the deep pit become on the copper foil of the pad, so that the gap between the opening area on the deep pit and the bottom of the stencil is reduced. After the small batch verification is OK, the original stencil is used for mass production, and the soldering of the soldering pads that are difficult to solder is good (the area of the soldering pad is increased, and no poor soldering is found in the batch verification);


2. Reduce the PCB solder mask thickness and the influence of the higher height solder mask layer on the circuit near the pad. Generally, it is recommended that the PCB solder mask thickness should be less than 25um.


3. The new PH stencil is used to eliminate printing gaps to the maximum extent. PH stencil is introduced.







Grandes SMT Assembly Advantages


1. Strength Guarantee


▪ SMT factory: With imported SMT machines and multiple optical inspection equipment, which is able to produce 4 million points per day. Each process is equipped with QC personnel who will keep an eye on product quality.

▪ DIP production line: Two wave soldering machines and more than 10 employees who have worked for over three years. That’ s to say, these workers are highly skilled and can weld various SMT & DIP components.


2. Quality Assurance With High Cost Performance


▪ High-end equipment can paste precision special-shaped parts, BGA, QFN, 0201 package. It can also be soldered prototype pcba via SMT machine and placing bulk materials by hand.

▪ Both samples, small and large batches can be produced. And there is no SMT Machine starting cost.


3. Rich Electronic Products SMT Soldering Experience With Stable Delivery


▪ Accumulated services to thousands of electronics companies, involving SMT soldering services for various types of automotive equipment and industrial control motherboards. Furthermore, PCBA products are often exported to Europe and the United States, and the quality is able to be affirmed by new and regular customers.


4. Strong Maintenance Ability & Reliable After-Sales Service


▪ The maintenance engineers have sophisticated experience so that those defective boards caused by all kinds of smt soldering can be repaired. Meanwhile, ensuring the connectivity rate of each circuit board also make sense.

▪Order problems feedback will get response, solution and solved as soon as possible.


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