Composition and function of SMT solder paste

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Solder paste is an critical element of SMT output process. The scale of steel powder in solder paste, the distribution of metal written content, the proportion of flux, rewarming time, stirring time, storage ecosystem and storage time of solder paste will affect the printing high-quality of solder paste.

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The composition of SMT solder paste may be divided into two components: flux and solder powder.

(1) The key components and features of flux are as follows

Thixotropic agent: this part is principally used to regulate the viscosity and printing functionality of solder paste to circumvent the looks of tailing and adhesion in printing;

Activator: this component can take out the oxide about the area of PCB copper movie pad plus the welding areas of areas, and reduce the surface rigidity of tin and guide;

Solvent: the ingredient would be the solvent of flux part, which performs an excellent purpose during the mixing method of solder paste, and it has a particular impression about the provider everyday living of solder paste;

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Resin: it can maximize the adhesion of solder paste, guard and stop PCB from reoxidation after soldering. It plays a very important part in repairing pieces;

(2) Solder powder:

Alloy solder powder will be the principal part of solder paste, accounting for 85-90% from the solder paste top quality. The typically used alloy welding powders are as follows: Sn Pb, Sn Pb AG, Sn Pb Bi, Sn Bi, Sn Bi Ag and Sn Ag Cu. The composition and ratio of solder powder, its condition, particle sizing and area oxidation diploma have fantastic impact over the homes of solder paste.

Once the steel information is higher, the slump of solder paste is usually enhanced, that is conducive on the development of total solder joints. Owing on the rather small degree of flux, it might reduce the flux residue and efficiently avert the looks of solder beads. Its drawback is the fact that the printing and welding procedure demands are demanding. When the metal content is lower, the printability is nice, the solder paste is just not simple to stay on the scraper, the service lifetime on the bushing is extended, the wettability is good, as well as processing is simple; the downside is usually that it’s simple to break down, as well as defects these types of as solder beads and bridging are easy to appear. As a result, it can be necessary to select acceptable tin powder technical specs.

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The form of alloy solder powder might be divided into spherical shape and oval form. The spherical solder has excellent attributes. The particle sizing of solder powder is two hundred / 325, which involves finer metal particle size for fine spacing printing. Frequently, the dimensions and condition of tin powder particles are based on the opening size of printing steel mesh or steel mesh or the diameter of syringe. Tin powder with unique particle dimension ought to be picked for various pad measurements and element pins, and compact particles should not be chosen for the reason that little particles have a great deal more substantial area space, which can be quick to aggravate the burden of solder through surface area oxidation treatment method.

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