How to Select Alloy for Solder Preforms

When it comes to PCB assembly applications that need use of precise amounts of alloy, solder preforms are extensively used as a viable solution to the requirement. These products are generally available in standard shapes, the most common being squares, rectangles, washers, and discs. Sizes tend to vary on the basis of your chosen supplier of solder preforms and your custom requirement, if any. Dimensions of the preforms are usually held to tight tolerances to ensure accuracy and consistency in volume of alloy used. In most cases, these products are available in terms of the exact specifications that a manufacturer desires. The matter that remains, therefore, is selecting the right alloy for solder preforms.

Types of alloys for solder preforms

Every manufacturer should make sure that the solder preforms alloy they select happens to be the most suitable alternative for their specific process and PCB requirements. Of course, in most cases, this happens to be a workable compromise between all factors that are important including bond strength, flow temperatures, compatibility and cost effectiveness. Solders are usually categorized into six types, namely those based on Gallium, Bismuth, Indium, Tin, Gold, and Lead. Other elements like Antimony, Cadmium, Zinc, Copper and the like are alloyed together with these six to create hundreds of solder combinations that all present different features and properties relevant for different PCB manufacturing purposes.

Selecting the alloy for your solder preforms

The choice of alloy for your solder preform requirements depends on a variety of factors, including:

• The alloy should have a melting temperature that is at least 50°C higher than the operational temperature of the parts being soldered. This will ensure that the alloy doesn’t obtain flow consistency again as a result of using the circuit board and the heat that electrical conductivity generates.

• The alloy for your solder preform should, on the other hand, have a lower melting temperature as compared to that of the surfaces and components being soldered together along with the circuit board substrate. This will minimize heat damage and distortion of surrounding areas when the solder achieves flow consistency.

• Metal compatibility is the next most important factor to consider when choosing an alloy for solder preforms. For example, tin-based solders tend to aggressively destroy gold from gold-plated parts and hence, this combination will result in formation of brittle joints and intermetallic. These factors should be kept in mind before you select your preferable alloy type.

• Ease of operations and use is another important factor to consider. Certain metals and alloys are much easier to transform into various shapes and thicknesses. This ease of handling and use can affect the cost effectiveness and process timelines of your PCB assembly operations.

• The mechanical capabilities of the alloy will also affect your solder preform selection. Temperature resistance, mechanical fatigue, possibility of damage from vibrations and impact, strength, durability, and corrosion resistance of the alloy – these are important factors to consider.

The above pointers should serve as a viable guide in your selection of the right alloy for your solder preforms. Use it well.

Alpha Assembly Solutions Inc. is the global leader in the development, manufacturing and sales of innovative specialty materials used in a wide range of industry segments, including electronics assembly, power electronics, die attach, LED lighting.