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Grape Ball Effect Causes the Effective Life of Solder Paste after Printing_Shenzhen Fitech

2023-09-15

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Grape Ball Effect Causes the Effective Life of Solder Paste after Printing

Grape ball effect refers to the SMT reflow process, the paste can not be completely melted and wet pads, and the formation of a small ball similar to grapes, affecting the reliability and appearance of the solder joints. The causes of the grape ball effect is mainly related to the quality of the solder paste, printing process, reflow profile and other factors. In this paper, we will focus on analysing the effective life of the solder paste after printing on the impact of the grape ball effect.


Solder paste printing effective life

The effective life after printing of solder paste refers to the time after the printing of solder paste on the PCB, at room temperature can maintain a good printing shape and performance. Reasonable management of the effective life is critical to the control of the grapevine effect, as the solder paste may oxidise, dry out and collapse after exceeding the effective life, leading to a reduction in print quality and increased soldering risk.

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Factors affecting the effective life of solder paste after printing

The post-press life of solder paste is affected by a number of factors, including the brand, type, formulation and storage conditions of the paste. Solder pastes from different manufacturers may have different effective life, usually between 2 and 8 hours.

Stencil opening size and board in-line time also affect solder paste life. The printed PCB is called a solder paste board, and the effective exposure time of the board in air shrinks as the stencil aperture size decreases. The smaller the stencil aperture size, the thinner the stencil, the smaller the amount of printed solder paste, the faster the drying of the paste, the mechanism and the evaporation of water droplets on the glass is consistent: the larger the droplets, the slower the disappearance, and vice versa, the faster the disappearance.

 

In order to avoid problems caused by the expiration of the effective life of the solder paste after printing, the following are some suggested measures:

Use solder paste in strict accordance with the instructions and specifications provided by the solder paste manufacturer, and observe the use period and storage conditions after opening.

Reasonably arrange the printing quantity and time according to the production plan to avoid the solder paste being exposed to air for a long time.

Regularly check the status of the solder paste on the printing plate, and replace or replenish fresh solder paste if any abnormality is found.

Use a special viscosity tester or other methods to test the viscosity of the solder paste to ensure that it is within the appropriate range.

Stir the solder paste with a stirring tool to make it uniform and consistent and avoid layering or settling.

Feed the printed board into the reflow oven as soon as possible before reflow to shorten the residence time and reduce oxidation and volatilisation.

Choose a suitable reflow profile to ensure that the solder paste can completely melt and wet the pads to form a complete solder joint.


Fitech Solder Paste

Printing solder pastes produced by Shenzhen Fitech have excellent printing performance, under-tin release performance and long time in-line performance up to 8 hours, as well as excellent slumping and thixotropic performance. For more information, please feel free to contact us.

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