Electrical and Frictional Performance of Tin-Coated Contacts Exposed to Wear and Fretting Corrosion

Sammanfattning: The complexity of electronic systems in vehicles is rapidly increasing, and as a consequence, the long-term reliability of automotive connectors has become an important issue. The aims of this thesis have been:1. to characterize the friction, wear and electrical properties of tin coatings,2. to achieve an improved fundamental understanding of the deterioration processes caused by wear and fretting corrosion,3. to propose improvements of tin coatings systems for electrical connectors.The required insertion force has a significant impact on the design and the cost of a connector. A reduced insertion force can be achieved by reduced contact load and/or reduced tin coating thickness, but this will increase the risk of fretting corrosion. Wear during the insertion stroke is essential in order to wipe off the non-conductive oxide layer. However, a thin tin layer may become worn off after only a few insertion strokes. The rider will then partly slide on the hard intermetallic compound formed between the substrate and the residual tin. Due to the restricted wear when sliding on the intermetallic compound more oxide will be formed during sliding than is removed and consequently the electrical contact resistance will increase.Two semi-empirical models are proposed, the first describing the contact resistance when the rider plows the free tin layer, and the second describing the contact resistance increase due to oxidation when the rider slides on the intermetallic compound.Two novel methods to improve the performance of pre-tinned material were evaluated. The first involves the use of a lubricant in combination with a textured surface, to improve the supply of lubricant into the contact spot. The second involves the addition of small amounts of a preferential oxidation additive to the tin. This increases the possibility of achieving a cold-welded contact spot, which results in an ultimately stable connection.