Measuring plating thicknesses using the MetaScope 3

At higher frequencies electrical conductors experience a current displacement towards the surface called skin effect. In general a thick silver coating is used in high frequency applications. It is important to have a uniform plating thickness without any variations which can alter the conductor cross section and impact negatively on the conductor resistance.

Many conductive materials form an oxide layer when exposed to a normal atmosphere. This can cause problems when the material is further processed especially when it is exposed to high temperatures, e.g. when running conductors through an extrusion line.

Plated conductors are primarily used in automatic process equipment to ensure a good contact. Avoiding contact corrosion or the build up of local cells improves the fatigue life of crimp connections.

Most standards and specifications require a minimum plating thickness. These are acceptance criteria for customers and it may be necessary to demonstrate exact results.

Especially when using high value precious metals it is possible to significantly optimise process costs by tightly controlling plating thicknesses.

A probe is immersed into a relevant electrolyte and connected to a measuring device using a test lead. As soon as the power is switched on the plating material begins to separate itself from the conductor.

To conduct the measurement the amount of electrical charge (Q) is required. This can be determined using the following equation: Q = It (As)
where Q is the amount of electricity in coulombs, I is the current in amperes and t is the time in seconds. A constant current and exact time measurement are needed to obtain accurate results.

The graph depicts a typical example for silver plated copper. The abrupt end of the gradual increase signals the total removal of the silver plating. This point, caused by a change in resistance determines the measuring time (t).

Components and assembly of
MetaScope 3

1. Power lead connector
2. Clamp to hold probe in place
3. Probe
4. Glass container for electrolyte
5. Copper cathode
6. Measuring device with software

The measuring device has a new brushed stainless steel housing. The introduction of the new 5.7” TFT touch screen has significantly simplified the test process. Following many years of experience the magnetic stirrer has been greatly improved. It now has a black PVC base complete with a “start” button and the stirrer now has a 7 step speed setting. The base is now compatible with 107mm diameter glass containers.

In contrast to the previous model the Metascope 3 now measures with probes (test pieces) of variable diameters and lengths which are entered before each measurement. In order to ensure a constant current the software compensates for fluctuations by adjusting the current ± 10% of the nominal current of 0.5 Amps. In addition the transfer time is accurately determined using two algorithms. This significantly improves the accuracy of each measurement. The test results along with additional information including customer, job number, name of test, date, etc are recorded and stored on the device’s hard drive and can be exported using a USB memory stick.

• Greater accuracy in determining the exact plating thickness
• Improved plating quality
• Process control
• Reduced consumption of high value plating metals during production
• Cost savings through reduction in usage of materials

LEONI

Technical article in German language in trade magazine "DRAHT" 1/2013:
http://www.drahtmagazin.de/draht-fachartikel/ schichtdicke-exakt-gemessen _22365_de/