Warton Metals offer customers the opportunity of regularly monitoring the quality of the solder in their machine and production lines. For completely unbiased results, Warton use an independent UKAS approved assay office.
If you require further information please contact us.
A solder bath or pot can become contaminated in various ways. The solder can already include impurities when received, especially if the supplier uses re-cycled materials, or it may become contaminated over a period of time by leaching copper and other contaminants from the work being soldered.
Many contaminants such as silver and bismuth are not specifically detrimental in small quantities, therefore are only an indication of the purity of the solder. Contaminants such as aluminium, cadmium and zinc however are very detrimental to the performance of the alloy. Non metallic impurities such as sulphur and phosphorous are dangerous to the solder in as much as they can cause de-wetting conditions.
Some inclusions can be considered as either alloying additions or contaminants depending on particular applications. Other inclusions must be avoided at all costs. A description of the effect of impurities in a solder bath, some common contaminants and how they can have an effect on solderability, dross creation, joint formation and wetting ability are shown in the table below.
| Element | Problem |
|---|---|
| Aluminium |
As little as 0.005% may increase dross rate without affecting joint formation. 0.001% may result in a sluggish or gritty solder. No solid solubility of aluminum in tin or aluminium in lead. |
| Antimony |
Certain of the specifications require the intentional addition of antimony. Ostensibly this is to retard the transformation of tin into its grey state, sometimes known as 'tin pest'. However this argument no longer appears to have validity in a eutectic or near eutectic alloy. |
| Arsenic |
0.03% can cause dewetting but arsenic is not usually a contaminant in electronic applications. |
| Bismuth |
0.5% has been observed to cause some discoloration and oxidisation of solder, but appreciable amounts of bismuth would not normally be present in high quality electronic grade alloys or finishes. Bismuth can be added to increase spread or to dull joints otherwise bismuth is a contaminant which increases oxidisation. |
| Cadmium |
A levels of 0.002% joint formation will be noticeably affected. At 0.005% there will be a high incidence of bridging and icicling, together with a deterioration in joint strength and a reduced rate in spread. Also a health risk if high percentages are present. |
| Copper |
Can increase the rate of spread slightly but over 0.25% copper or even less joint formation will have deteriorated and could lead to dewetting and grittiness. |
| Gold |
At levels of 0.1% and quite often even less, the solder becomes sluggish and dull joints are formed. |
| Iron |
0.02% of iron can make joint formulation gritty. |
| Sulphur |
As little as 0.001% may inhibit wetting and produce grittiness. |
| Silver |
Has little effect on the wetting properties of tin/lead solders although it can be added to suit certain applications. |
| Sulphur |
The presence of zinc can cause dulling and increase bridging and icicling. 0.005% can cause lack of adhesion and grittiness. |
When copper and gold in combination add to 0.25%, joint formation will usually have deteriorated. The effects of aluminium, cadmium and zinc are cumulative. If more than one element is present the following lower limits are suggested 0.0005%, 0.002% and 0.001%.
To find out the quality of your solder bath, take a small sample (about the size of a fifty pence piece) from the wave of the solder machine and send it to Warton Metals for analysis. Each sample should have an accompanying 'application for analysis' filled in. Warton will send the sample to the UKAS approved assay office and results should be with you within 2 weeks. If any contaminants are present in the results, Warton will be happy to advise on a solution.
Please fill in the form to find out the cost, or to request an application for analysis.