Basic Requirements for Lead-free Electronic Solder in Electronic Assembly
Release time:
2022-09-23
【Summary Description】 Most (but not all) assembly manufacturers require a minimum solid phase temperature of 150°C to meet the operating temperature requirements of electronic equipment, and the maximum liquid phase temperature depends on the specific application. Good conductivity This is the basic requirement for electronic solder connection. Good thermal conductivity In order to dissipate heat energy, electronic solders must have rapid heat transfer capabilities. Smaller solid-liquid coexistence temperature range Non-eutectic alloy will solidify in a certain temperature range between liquid phase temperature and solid phase temperature. Most metallurgical experts recommend that this temperature range be controlled within 10 ℃ in order to form good solder joints and reduce defects. If the alloy solidification temperature range is wide, solder joint cracking may occur, causing premature damage to the equipment. Low-toxicity electronic solders and their components must be non-toxic, so this requirement excludes cadmium, thallium and mercury from consideration; some also require that byproducts extracted from toxic substances cannot be used, thus excluding bismuth, which is mainly derived from byproducts extracted from lead. Have good solderability Under the conditions of existing equipment and no-clean flux, the electronic solder should have sufficient wettability to be able to be used with regular no-clean flux. Because the cost of inert treatment of the wave crest is not too high, it can accept the requirements of wave soldering and inert environment, but in the case of SMT reflow, the alloy is best to have the ability to reflow under air, because the cost of inert treatment of the reflow furnace is higher. Good physical properties (strength, elongation, fatigue, etc.) The electronic solder must be able to provide the mechanical strength and reliability of 63Sn/37Pb, and will not have protruding fillet welds on the through hole device (especially for alloys with large solid-liquid coexistence temperature range). Production repeatability/melting point consistency. The electronic assembly process is a high-volume manufacturing process that requires a high level of repeatability and consistency. If the composition of some electronic solders cannot be repeatedly manufactured under high-volume conditions, or If its melting point changes greatly due to composition changes during mass production, it cannot be considered. Electronic solders composed of more than three components tend to be separated or changed in composition, so that the melting point cannot be kept stable. The higher the complexity of the alloy, the greater the possibility of its change.
Most (but not all) assembly manufacturers require a minimum solid phase temperature of 150°C to meet the operating temperature requirements of electronic equipment, and the maximum liquid phase temperature depends on the specific application.
Good conductivity This is the basic requirement for electronic solder connection.
Good thermal conductivity In order to dissipate heat energy, electronic solders must have rapid heat transfer capabilities.
Smaller solid-liquid coexistence temperature range Non-eutectic alloy will solidify in a certain temperature range between liquid phase temperature and solid phase temperature. Most metallurgical experts recommend that this temperature range be controlled within 10 ℃ in order to form good solder joints and reduce defects. If the alloy solidification temperature range is wide, solder joint cracking may occur, causing premature damage to the equipment.
Low-toxicity electronic solders and their components must be non-toxic, so this requirement excludes cadmium, thallium and mercury from consideration; some also require that byproducts extracted from toxic substances cannot be used, thus excluding bismuth, which is mainly derived from byproducts extracted from lead.
Have good solderability Under the conditions of existing equipment and no-clean flux, the electronic solder should have sufficient wettability to be able to be used with regular no-clean flux. Because the cost of inert treatment of the wave crest is not too high, it can accept the requirements of wave soldering and inert environment, but in the case of SMT reflow, the alloy is best to have the ability to reflow under air, because the cost of inert treatment of the reflow furnace is higher.
Good physical properties (strength, elongation, fatigue, etc.) The electronic solder must be able to provide the mechanical strength and reliability of 63Sn/37Pb, and will not have protruding fillet welds on the through hole device (especially for alloys with large solid-liquid coexistence temperature range).
Production repeatability/melting point consistency. The electronic assembly process is a high-volume manufacturing process that requires a high level of repeatability and consistency. If the composition of some electronic solders cannot be repeatedly manufactured under high-volume conditions, or If its melting point changes greatly due to composition changes during mass production, it cannot be considered. Electronic solders composed of more than three components tend to be separated or changed in composition, so that the melting point cannot be kept stable. The higher the complexity of the alloy, the greater the possibility of its change.
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