Changes

The primary requirement on an electroplated deposit is its thickness since a series of other properties such as porosity, hardness, and ductility, are depending on the layer thickness. A widely used method for thickness measurement is the one using microscopical evaluation of a mounted micro

thicknesses the X-ray fluorescence method is used which often is integrated for quality assurance into the manufacturing process, for example in selective reelto- reel electroplating plating lines. In this process the returned characteristic xray impulses of the coating material and the substrate, generated by the primary x-rays, are detected and counted and then converted into material thickness by a computerized indicator or recording and control unit.

Pores are surface defects which may have multiple causes. These include roughness and defects in the substrate layer or material such as grooves or

At the foot points of the pores the substrate material is exposed to the surrounding atmosphere. This can cause corrosion products to rise through the pores to the contact surface, expand there further, and thus lead to increased contact resistance. The allowable number of pores in gold layers, for example for connectors, mainly depends on the concentration of corrosive gases in the intended working environment.

Frequently a SO test at higher concentrations (100 ppm) and high humidity 2 levels (95% RH at 40°C) is used. One advantage of this method is that the severity level can be increased easily by varying the concentration of SO₂. Besides these, other corrosive gas mixtures of H₂S, SO₂, and NO₂ are used in porosity tests (i.e. tests according to ASTM B735 and B 799).

The hardness of electroplated surface coatings depends on their deposition parameters and therefore on the structure and concentration of incorporated substances. The hardness measurement is however not a true indicator of the mechanical properties such as frictional wear characteristics like for clad meltmetallurgically produced layers. This is caused by their fundamentally different structure compared to alloys. Brittleness and internal stresses also have an influence on the hardness.

A decrease in hardness can then be observed towards the layer's surface.

The ductility indicates how much a coating layer can be plastically deformed without cracking. Therefore it is an important measure for the quality of electroplated coatings.

If the ductility is too low, cracks can develop in the layer. This crack formation can occur due to internal stresses right after the deposition or develop from mechanical stressing during subsequent mechanical deformation.

For contact parts which are subjected to frictional sliding between each other, such as for example connector or sliding contact parts, the frictional wear is the determining factor for contact life and reliability. In general it is assumed that harder surfaces are more wear resistant. This usually is true for molten alloys, but not necessarily the fact for electroplated surface layers. As an example, low-carat molten AuCuCd layers exhibit despite a high hardness (HV 350) a higher mechanical wear than high-carat electroplated hard gold coatings (HV 120).

In the latter the incorporated carbon content acts as a lubricant, reducing wear significantly. Comparative tests of the mechanical wear of contact layers are After these additional testing will be performed, for example on actual connectors which then incorporate the real design characteristics in the connector contact area.

The contact resistance is the most important functional property determining the reliability of a contact layer.

The measuring voltage and current are usually in the range of < 20 mV and, 10 mA (DC or 1 kHz AC). The contact force is selected as 2, 5 or 10 cN,

Good adhesion of the electroplated layer on the substrate is mandatory for the reliable function of a contact system. The adhesion strength between the electroplated surface coating and the substrate depends on many factors, such as the surface roughness of the carrier metal, the surface preparation, thermal expansion properties, ductility, and others. A difference in formability of layer and substrate metal can easily lead to separation of the coating layer. Rapid temperature changes can also lead to delaminating if the thermal coefficients of expansion of the coating and the substrate differ substantially. A prerequisite for good adhesion is the careful surface preparation prior to the actual electroplating, which is usually integrated into the electroplating process equipment.

Quite often temperature tests are also used to judge the adhesion strength. For these samples are exposed to elevated temperatures between 120 and 400°C over a defined time period (5 to 60 min). At insufficient bonding strength bubbles are becoming visible and delaminating may occur.

In this context soldering is defined as using low temperature tin or tin alloys. A freuquently used method to determine the solderability is the immersion test. The coated material is inserted into a bath of the liquid solder and tinned for about 5 s. After this exposure 95% of the surface immersed must be wetted with the solder.

Gold is known to be well solderable, however problems can occur when soldering onto thin gold layers. Since the gold quickly dissolves in the soldering alloy the viscosity of the liquid solder is increased and can lead to reduced wetting. Gold and tin also form intermetallic compound phases which lead to embrittlement and thus reduce the mechanical strength of the solder bond. In addition non-precious alloying components or co-deposited carbon can be problematic for good solderability.

The wire bonding – a welding process of fine wires onto flat semiconductors and metal surfaces – was developed for contacting semiconductor

*Pull Test

==References==

[[Testing Procedures#References|References]]