EP3070188A2 - Method for coating a press-in pin and press-in pin - Google Patents

Abstract

The invention relates to a method for coating a press-fit, wherein a base body made of copper or a copper alloy is galvanically coated from an alkaline cyanide electrolyte with a layer of a silver alloy containing more than 50 wt.% Ag, a balance of Sn and unavoidable Contains impurities.

Description

The invention relates to a method for coating a press-fit pin and a press-in pin.

The EP 2 596 157 B1 discloses a method of making a press-fit pin. In this case, a layer is deposited on a base body galvanically from methanesulfonsaurer solution, which is formed from a tin alloy.

The US 2009/0239398 A1 discloses a press-in pin which is coated with a layer made of a tin alloy. The tin alloy contains 0.5 to 15 wt.% Silver.

The US Pat. No. 6,361,823 B1 discloses an electroless method for coating a base made of copper or a copper alloy. In this case, the base body is first coated with a layer made of tin and then coated with an outer layer made of an alloy.

The DE 10 2005 055 742 A1 discloses a method of making a contactable layer on a metal element. The contact-adapted layer is formed essentially of tin. It may have intermetallic silver / tin phases with a silver content in the range of 25 to 40 wt.%.

The aforementioned coatings of a silver-containing tin alloy replace earlier coatings made from lead-containing tin alloys. The replacement is required because of EU Directive 2002/95 / EC, which prohibits the use of lead as an environmentally hazardous substance.

In the case of a layer made of a silver-containing tin alloy, however, in practice the formation of whiskers growing out of the layer sometimes occurs. Such whiskers can lead to the formation of short circuits.

The object of the invention is to eliminate the disadvantages of the prior art. In particular, a method for producing a press-fit pin and a press-in pin are to be specified in which the tendency to form whiskers is reduced.

This object is solved by the features of claims 1 and 14. Advantageous embodiments of the invention will become apparent from the features of claims 2 to 13 and 15 to 23.

According to the invention, a method for coating a Einpresspins is proposed, wherein a base made of copper or a copper alloy is galvanically coated from an alkaline-cyanide electrolyte at least partially with a layer of a silver alloy, the more than 50 wt.% Ag, a Contains residual Sn and unavoidable impurities.

In departure from the prior art, the layer is not deposited galvanically from an acidic electrolyte, but from an alkaline-cyanide electrolyte on the base body. The silver alloy forming the layer contains more than 50% by weight of Ag, preferably at least 55% by weight of Ag. It has surprisingly been found that with the method according to the invention, a largely pore-free connection of the layer to the base body can be achieved. In particular, it is possible with the proposed method to produce homogeneous single-phase layers. A press-in pin produced by the method according to the invention is characterized by a particularly low tendency to form whiskers.

For the preparation of the electrolyte, one of the following silver compounds can be used: silver cyanide, potassium silver cyanide, silver sulfide, silver sulfate. As tin compounds, the following compounds can be used to prepare the electrolyte: potassium stannate, sodium stannate, tin oxide, tin sulfate.

Furthermore, at least one of the following compounds is advantageously added to the electrolyte: sodium cyanide, potassium cyanide, sodium gluconate, potassium gluconate, ethylenediamine, ammonia, triethanolamine, glycine, thiourea, urea, nitrilotriacetic acid. The abovementioned compounds serve as complexing agents or as conducting salts.

Furthermore, at least one of the following further compounds may be added to the electrolyte: sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, potassium sulphide. The abovementioned further compounds act as complexing agents with respect to tin. Apart from that, the conductivity of the electrolyte can be adjusted with the other compounds.

The galvanic coating is advantageously carried out at a current density in the range of 5 to 20 A / dm ² . The pH of the electrolyte is suitably adjusted to 7 to 14, preferably to more than 8. A temperature of the electrolyte may be adjusted to a value in the range of 40 to 90 ° C, preferably 50 to 70 ° C in the coating. More preferably, the temperature is 55 to 60 ° C.

As the anode, an anode made of any one of the following materials can be used: graphite, platinum-plated titanium or niobium, silver, tin, silver or tin alloy. An anode made of titanium or niobium may also be coated with a layer of a mixed oxide based on Ir, Ta, Nb instead of the platinum. It is also possible to use an anode made of silver and a further anode made of tin, which are operated in two separate circuits. Further, anodes can be used in an anolyte with a diaphragm.

According to an advantageous embodiment of the invention, the layer in a thickness of 0.1 to 0.8 microns, preferably 0.2 to 0.6 microns applied. Before applying the layer formed from the silver alloy, an intermediate layer of Ni or Cu can be galvanically applied to the base body. Thus, the adhesion of the layer can be improved.

According to a further embodiment, the applied to the body layer for a period of 1 to 10 seconds to a temperature in the range of 200 to 500 ° C, preferably 300 to 400 ° C, heated. The heating causes a crystal growth in the layer. Furthermore, it can be reduced in the alloy, the concentration of Sn. As a result, intermetallic phases can form Ag ₃ Sn or Ag ₄ Sn. Such intermetallic phases are particularly effective against the formation of whiskers.

Further, the heat treatment may cause the formation of further intermetallic phases between the base body and the layer. Such further intermetallic phases consist for example of Cu ₆ Sn ₅ or of Cu ₃ Sn. If an intermediate layer made of Ni is provided on the base body, the heat treatment may cause the formation of a further intermetallic phase between the Ni intermediate layer and the layer made of the silver alloy. Such a further intermetallic phase is formed, for example, from Ni ₃ Sn ₄ .

According to another aspect of the invention, a press-in is proposed, with a base body made of copper or a copper alloy and the base body at least partially covering layer, wherein the layer is formed of a silver alloy containing at least 50 wt.% Ag, a balance of Sn and contains unavoidable impurities. The proposed press-in pin can be produced by the process according to the invention. It advantageously contains no lead. With the proposed layer, formation of whiskers can be effectively counteracted.

According to an advantageous embodiment of the invention, the silver alloy contains more than 63 wt.% And less than 90 wt.% Ag. Advantageously, the silver alloy contains 73% by weight to 89% by weight of Ag. Particularly preferably, the silver alloy contains 75 wt.% To 85 wt.% Ag.

The silver alloy is in particular formed from Ag ₃ Sn and / or from Ag ₄ Sn. It is in particular formed from an intermetallic phase of Ag ₃ Sn or Ag ₄ Sn. Such an intermetallic phase causes the formation of whiskers safely and reliably. Preferably, the silver alloy is greater than 95%, preferably greater than 99%, of a single such intermetallic phase.

The silver alloy may also be formed from an Ag or Sn matrix containing at least one intermetallic phase of Ag ₃ Sn and / or Ag ₄ Sn.

A thickness of the layer is suitably 0.1 to 0.8 μm, preferably 0.2 to 0.6 μm. The thickness of the layer is particularly preferably 0.3 to 0.4 μm.

According to a further advantageous embodiment of the invention, an intermediate layer formed of Ni or Cu is provided between the base body and the layer. The intermediate layer may have a further thickness of 1.0 to 3.0 μm, preferably 1.1 to 2.5 μm.

An average crystal size of the crystals forming the layer is advantageously 50 to 800 nm, preferably 100 to 600 nm, particularly preferably 150 to 400 nm.

Hereinafter, an embodiment of the invention will be explained in more detail.

For coating an electrical connector, in particular a Einpresspins, according to the inventive method, an electrolyte is used, the composition of which is shown in the table below. <U> Table </ u> additive concentration silver cyanide 0.5-10 g / l potassium stannate 20-140 g / l sodium cyanide 20-140 g / l sodium hydroxide 5-120 g / l

In particular, the pH of the electrolyte is adjusted to a value in the range of 8 to 13 by the addition of sodium hydroxide, potassium hydroxide or the like. The electrolytic deposition of the layer takes place at a temperature in the range of 50 to 70 ° C. and a current density of 5 to 20 A / dm ² .

Advantageously, the concentrations of the silver and tin-providing compounds are adjusted so that a single-phase intermetallic compound of Ag ₃ Sn or Ag ₄ Sn is formed.

The layer deposited on the base made of copper or a copper alloy may subsequently be heated to a temperature in the range of 300 to 400 ° C for a period of 1 to 10 seconds.

The press-in pin produced according to the invention is free of lead. The layer of silver alloy deposited thereon is hard, tough, and has a particularly low tendency to form whiskers.

Claims (24)

A method for coating a press-fit, wherein a base body made of copper or a copper alloy is galvanically coated from an alkaline-cyanide electrolyte at least partially with a layer of a silver alloy containing more than 50 wt.% Ag, a balance of Sn and unavoidable impurities , The process of claim 1, wherein one of the following silver compounds is used to prepare the electrolyte: silver cyanide, potassium silver cyanide, silver sulfide, silver sulfate. Method according to one of the preceding claims, wherein one of the following tin compounds is used to prepare the electrolyte: potassium stannate, sodium stannate, tin oxide, tin sulfate. Method according to one of the preceding claims, wherein at least one of the following compounds is added to the electrolyte: sodium cyanide, potassium cyanide, sodium gluconate, potassium gluconate, ethylenediamine, ammonia, triethanolamine, glycine, thiourea, urea, nitrilotriacetic acid. Process according to one of the preceding claims, wherein at least one of the following further compounds is added to the electrolyte: sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, potassium sulphide. Method according to one of the preceding claims, wherein the galvanic coating at a current density in the range of 5 to 20 A / dm ^{2 is} performed. Method according to one of the preceding claims, wherein the pH of the electrolyte is adjusted to more than 7, preferably to more than 8. Method according to one of the preceding claims, wherein a temperature of the electrolyte in the coating to a value in the range of 40 to 90 ° C, preferably 50 to 70 ° C, is set. Method according to one of the preceding claims, wherein an anode made of one of the following materials is used as the anode: graphite, platinized titanium, platinized niobium, silver, tin, silver alloy, tin alloy. Method according to one of the preceding claims, wherein the layer in a thickness of 0.1 to 0.8 microns, preferably 0.2 to 0.6 microns, is applied. Method according to one of the preceding claims, wherein an intermediate layer of Ni or Cu is applied galvanically to the base body prior to the application of the layer formed from the silver alloy. Method according to one of the preceding claims, wherein the intermediate layer in a further thickness of 1.0 to 3.0 microns, preferably 1.1 to 2.5 microns, is applied. Method according to one of the preceding claims, wherein the applied to the base layer for a period of 1 to 10 seconds to a temperature in the range of 200 to 500 ° C, preferably 300 to 400 ° C, heated. Einpresspin with a base body made of copper or a copper alloy and a body at least partially covering the layer, wherein the layer is formed of a silver alloy containing more than 50 wt.% Ag, a balance of Sn and unavoidable impurities. A press-fit pin according to claim 14, wherein the silver alloy contains more than 63% by weight and less than 90% by weight Ag. A press-fit pin according to claim 14 or 15, wherein the silver alloy contains 73% by weight to 89% by weight Ag. A press-fit pin according to any one of claims 14 to 16, wherein the silver alloy contains from 75% to 85% by weight of Ag. A press-fit pin according to any one of claims 14 to 17, wherein the silver alloy is formed of Ag ₃ Sn and / or Ag ₄ Sn. A press-fit pin according to any one of claims 14 to 18, wherein the silver alloy is formed of an intermetallic phase of Ag ₃ Sn or Ag ₄ Sn. A press-fit pin according to any one of claims 14 to 19, wherein the silver alloy is formed of an Ag or Sn matrix containing at least one intermetallic phase of Ag ₃ Sn and / or Ag ₄ Sn. A press-fit pin according to any one of claims 14 to 20, wherein a thickness of the layer is 0.1 to 0.8 μm, preferably 0.2 to 0.6 μm. Press-fit pin according to one of claims 14 to 21, wherein between the base body and the layer, an intermediate layer formed of Ni or Cu is provided. Press-fit pin according to one of claims 14 to 22, wherein the intermediate layer has a further thickness of 1.0 to 3.0 microns, preferably 1.1 to 2.5 microns. A press-fit pin according to any one of claims 14 to 23, wherein an average crystal size of the crystals forming the layer is 50 to 800 nm, preferably 100 to 600 nm, particularly preferably 140 to 400 nm.