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What factors should be considered in the selection of PCBA solder paste?
Jun 09, 2018

Solder paste is much more complex than pure tin-lead alloys. The main components are as follows: solder alloy particles, fluxes, rheology modifiers, viscosity control agents, and solvents. Indeed, it is necessary to grasp relevant factors and choose different types of solder pastes. At the same time, we must also choose the large-scale manufacturing process and stable quality. The following factors must be taken into consideration when selecting the solder paste:


1, the viscosity of solder paste


The viscosity of the solder paste is the most important factor affecting the printing performance. The viscosity is too high, the solder paste is not easy to penetrate through the opening of the template, the printed lines are incomplete, the viscosity is too low, and the flowability and edge collapse are easy to affect the resolution of the printing and The flatness of the lines.


The viscosity of the solder paste can be measured with an accurate viscometer. In actual work, if the manufacturer of the patch is purchasing imported solder paste, a simple method can be used to determine the viscosity in a simple way: use a spatula to pick up the solder paste and see if it is Slowly step by step to achieve moderate viscosity. At the same time, we also think that to make the solder paste has good viscosity characteristics for each use, we need to do the following:


(1) The production volume is small, and the solder paste is used repeatedly. It is necessary to formulate strict specifications. The solder paste outside the specifications must be strictly stopped.


(2) It is best to use a special stirrer for agitation;


(3) From 0 °C to room temperature, the seal and time must be guaranteed;



the uniformity and size of solder paste particles


Solder paste solder particle shape, diameter size and uniformity also affect the printing performance. Usually fine-grained solder paste will have better solder paste resolution, but it is prone to edge collapse, oxidation and opportunities. Pin spacing is usually one of the important selection factors, taking into account both performance and price.


the viscosity of solder paste


The stickiness of the solder paste is insufficient, and the solder paste does not roll on the template during printing. The direct result is that the solder paste cannot completely fill the opening of the template, resulting in insufficient deposition of the solder paste. If the viscosity of the solder paste is too high, the solder paste will hang on the wall of the template hole and not all of the solder paste will be printed on the pad.


The sticky choice of solder paste generally requires that its self-adhesive ability is greater than its bonding ability with the template, and its adhesive force with the template hole wall is smaller than its bond with the pad.


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