The solder ability of a substrate is a measure of the ease with which a soldered joint can be made to that material. Good solder ability requires wetting (low contact angle) of the substrate by the solder.
The procedure, considered to be destructive, tests whether the packaging materials and processes used during manufacturing operations produce a component that can be successfully soldered in the next level assembly.
There are two methods of testing device solder ability:
- Method 1 is known as ‘dip and look,’ which is for leaded and leadless terminations. It includes preconditioning if needed, the application of flux and the immersion of the terminations into molten solder. Dip and look solder ability testing is performed by subjecting the components to 0-8 hours of steam conditioning. After steam conditioning, the components’ terminations are dipped into the solder in a controlled fashion using a specific activated rosin flux. After dipping, the components are inspected to the criteria specified.
- Method 2 is a Surface Mount Simulation test. Surface mount simulation testing is performed by screen printing a specific solder paste onto a ceramic plate then placing the component onto the paste, followed by a specific convection reflow profile. Surface mount simulation testing can be used on all surface mount components including BGA and CGA which cannot use the dip and look method.
Solder Ability of Various Materials
| Solder Ability | Metals | Remarks |
| Excellent | Tin Cadmium Gold Silver Palladium Rhodium | Noble metals dissolve easily in solders, resulting in brittle joints. |
| Good | Copper Bronze Brass Lead Nickel Silver Beryllium Copper | High thermal conductivity of these metals requires high heat input during soldering, Oxidizes quickly so proper flux must be used. |
| Fair | Carbon steel Low Alloy Steel Zinc Nickel | Solder Joints became brittle in sulphur-rich environments. Avoid higher temperatures in the presence of lubricants (which contain sulphur). |
| Poor | Aluminium Aluminium Bronze | Tough oxides on the surface prevent wetting (formation of the inter-metallic layers). Solders have to be specially selected to avoid galvanic corrosion problems. Tin-zinc solders have proven to be reliable in joining aluminium to aluminium and aluminium to copper. They most often require flux and brushing with a stainless steel brush to break oxide coating to achieve proper bond. |
| Poor | High Alloy steel Stainless steels | Too much chromium oxide. The surface needs to be cleaned with an aggressive flux. |
| Very Difficult | Cast iron Chromium Titanium Tantalum Magnesium | May require pre-plating, or pre-tinning,[4] with a solder able metal or will require the use of a specialized solder. |
The inspection and failure criteria require:
- Removal of all flux prior to inspection of the terminal surface.
- Inspection of the devices at 10x to 20x magnification.
- A minimum of 95% solder coverage of each lead within the inspected area.
An exquisite illustration about the solder ability testing method and material bifurcation according to quality.
A one can use it for both leaded and lead-free components using Multi core Universal Solder ability Testers. Nowadays, in industries and research labs, such tests are difficult to replicate and are not suitable as standardised assessments.
Solder ability testing, utilising wetting balance technology, is a measurement of the weight and speed with which the solder meniscus climbs upwards on the component lead dipped in molten solder. When properly administered Wetting Balance measurement is by far the most accurate, quantitative method for measuring, testing and recording solder ability. Although the type of Wetting Balance used for through-hole (TH) and surface-mount (SM) components does differ, both are based on the same physical principals.
The wetting balance test method has for long been regarded as most versatile and has been used for assessing the efficiency of fluxes as well as the solder ability of the components. Examination of the results gives information about both the speed and extent of wetting and the behaviour of the surface upon prolonged exposure.
All components can be tested for solder ability. However, SIX SIGMA always considers the test to be destructive.