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How to Choose a Solder Paste according to Temperature Requirements?

2022-09-14

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How to Choose a Solder Paste according to Temperature Requirements?


In order to meet different packaging process requirements, in the actual process, the selection of solder paste products should match the packaging process temperature. How to choose solder pastes according to temperature requirements?

 

First of all, solder pastes can be divided into low-temperature, medium-temperature, and high-temperature categories according to the melting points or reflow temperatures. Low-temperature solder pastes usually refer to solder paste products with melting points lower than 160℃ or peak reflow temperatures lower than 200℃. High-temperature solder pastes usually refer to solder paste products with a melting point temperature above 240°C. The medium-temperature solder pastes are solder paste products with melting points between low-temperatures and high-temperature solder pastes.

 

The main factor that determines the melting and curing temperatures of solder paste is the alloy composition

At present, there are many types of solder pastes, such as low-temperature solder pastes represented by Sn42Bi57.6Ag0.4, medium-temperature solder pastes represented by SnAg3Cu0.5, high-temperature solder pastes represented by SnSb/SnSbNi, and special purpose solders represented by Au80Sn20. SnAg3Cu0.5 (melting point 217-219℃) and Sn42Bi57.6Ag0.4 (melting point 139℃) are the most popular products.

 

Process temperature is the important criterion for choosing a solder paste

Solder alloys are required to melt and wet the pads within the temperature range limited by the soldering process. The solder paste should be able to melt and effectively complete the soldering process with limited process temperatures. Excessively high or low temperature due to the mismatch between solder melting points and process temperatures is not beneficial for the formation of reliable solder joints.

 

Solder Paste Applications

Low-temperature solder pastes have low soldering temperatures, small thermal stress, small substrate warpage, and are energy saving and emission reduction, which are suitable for the packaging in temperature-sensitive components or processes such as FPCs, secondary and tertiary reflow in multiple reflows, etc. Medium-temperature solder pastes are currently the most widely-used solder paste product. It has a wide range of applications and good soldering effects. High-temperature solder pastes have high melting points and service temperatures, which are used in IGBTs, SMT zero-level packaging, and other fields.

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