Technical requirements for solder paste for PV?

The technical requirements for solder pastes for photovoltaics are quite stringent to ensure the solder quality and long-term reliability of PV modules.These technical requirements are summarised in detail below: 

1. Alloy components

Eutectic or near-eutectic properties: The alloy components of the solder paste should be as eutectic or near-eutectic as possible to ensure that the solder joints have high strength and good solderability with the PCB plating of the photovoltaic module, component ends or pins.This helps to ensure the strength of the solder joint and the stability of the electrical connection.

Proportion of alloy components: The proportion of alloy components in the solder paste should be adjusted according to the specific application requirements.For example, a common tin-silver-copper solder paste may have a component ratio of Sn3Ag0.5Cu, while a tin-bismuth-silver solder paste may have a component ratio of Sn35Bi1Ag. These alloy compositions are chosen to provide the required mechanical and electrical properties.

2. storage performance

Stability: solder paste should maintain good performance stability during storage to avoid chemical changes or degradation of physical properties.This includes the uniform mixing of alloy solder powder and flux, as well as avoiding the occurrence of delamination.

Shelf life: solder paste should have a clear shelf life, and in the shelf life to maintain good printing performance and welding effect.

3. the printing performance

Not easy to dry: solder paste in continuous printing at room temperature, it should not be easy to dry, in order to maintain its good printability and fluidity.

Good rolling properties: solder paste should have good rolling properties, so that in the printing process smoothly through the screen or leakage plate aperture, the formation of a uniform layer of solder paste.

Releaseability: After printing, the solder paste should be able to easily detach from the stencil to avoid residue and waste.This helps to maintain the clarity and accuracy of the printed pattern.

4. viscosity characteristics

Meet the process requirements: the viscosity of the solder paste should be adjusted according to the specific printing process to ensure that the release of printing and shape retention.Viscosity is too high may lead to printing difficulties, while viscosity is too low may lead to solder paste collapse or diffusion.

Thixotropy: Solder pastes should have good thixotropy, i.e., the viscosity decreases under external force, making it easier to print; the viscosity recovers after the external force is removed, keeping the shape and not collapsing.This helps to ensure the uniformity and stability of the solder paste layer after printing.

5. Solder powder

Particle uniformity: the particles of solder powder should be evenly distributed to reduce the concentration of thermal stress and welding defects in the welding process.

Micro-powder content: micro-powder content should be controlled within a certain range to avoid flux melting and vaporisation of the burst phenomenon, affecting the welding quality and appearance.

Wettability and spatter control: solder powder and flux should be formulated to ensure that the solder has good wettability during the reflow process and to reduce the spattering of solder balls.This helps to form dense, uniform solder joints and improve the reliability of the soldered joints.

Summary: The technical requirements of solder paste for photovoltaics cover a wide range of aspects such as alloying components, storage properties, printing properties, viscosity characteristics and solder powder.Together, these requirements ensure the quality and reliability of PV modules during the soldering process, thereby improving the performance and lifetime of the entire PV system.