What is Solderability

The ability of a metal to be wet by molten solder is known as solderability. A number of methods can measure solderability. The wetting force is measured and recorded as a function of time using a wetting balance. Despite being a quantitative test, there are issues when applying the findings to real-world soldering scenarios. It also calls for a costly piece of lab apparatus.

The solder bath dip and look test is a commonly used qualitative test. This test uses a solder pot, dipping mechanism, and power microscope, and it can call for the test samples to be aged in a steam bath. Both MIL-STD 202/208F and American National Standards ANSI/J-STD-002 provide clear instructions on how to use this test to determine if the wire is solderable.

Both bare and plated surfaces can be subjected to the solder bath dip and look test. The test is a broad indicator of surface oxides and cleanliness on bare surfaces. When used on plated surfaces, the test provides a reliable indication of the plated wire's solderability. In preparation for a subsequent assessment using the dip and look test, steam aging the plated samples encourages degradation through surface oxidation as well as intermetallic growth. Whether the solder is first steam aged or not, 95% wetting coverage is the general dip and look solderability acceptance criterion for the tested area.

CATEGORIES OF STEAM AGE

The ANSI/J-STD-002 solderability test recognizes three categories of steam aging.

CATEGORY 1

• No Need for Steam Ageing.
• Minimum Durability of the coating.
• Designed for surfaces that are expected to be exposed to at least some heat exposure and will be soldered shortly after the testing (e.g., within six months).

CATEGORY 2

• 1 Hour +/- 5 Min. Steam deterioration.
• Average Coating Durability (for finishes without tin and with tin-lead).
• Designed for surfaces coated with coatings other than Sn or Sn/Pb that will be soldered after a considerable amount of time has passed since the testing and may experience some minor heat exposure before soldering.

CATEGORY 3

• 8 Hours +/- 15 min. Steam deterioration.
• Average Coating Durability (standard for coatings made of tin and tin-lead).
• Designed for surfaces coated with Sn or Sn/Pb that will be soldered after being stored for an extended period (more than four months) following testing and being subjected to several heat exposures before soldering.

Metal finishing is the process of treating the surface of a metal product or component by adding or removing material. The importance of metal finishing is to alter the surface of the metal for good. 

SHELF-LIFE

In controlled circumstances, the link between steam aging and natural aging has demonstrated that appropriately plated tin and tin/lead systems that pass solderability after 8 hours of steam aging will continue to solder after 12 months and may continue to do so for an additional year. The maximum storage life of any plated wire cannot be precisely predicted due to the combined impact of the factors of the alloy base metal, underplates, surface geometry, and storage settings. To maximize plated copper alloy wire's solderability and shelf life, do the following:

• Use a copper or nickel underplate (recommended) over tin or tin-lead plating.
• Steer clear of tin or tin-lead coatings that have been artificially or organically brightened.
• The wire should be kept in its original packaging, ideally in a climate-controlled space.

DEFINITIONS

• WETTING – the process of a solder film adhering to a base metal in a largely uniform, continuous layer.
• DEWETTING – After coating a surface, molten solder recedes, leaving behind irregularly shaped mounds of solder divided by regions that are covered in a thin layer of solder, preventing the base metal from being seen.
• NON-WETTING – the base metal being exposed due to the partial adhesion of molten solder to a surface.
• PIN HOLES – Small holes that pierce through the base metal are imperfections in the wetted surface.
• SHELF-LIFE – The time frame, expressed in months and starting from the wire's plating date, within which the wire must pass a solderability test.