Patent Application
20130084760
The present invention relates generally to electrical connectors and in particular to plated electrical connector contacts.
A wide variety of devices are available for consumers today. Many of these devices have connectors that that facilitate communication with and/or charging of the corresponding device. These connectors often interface with other connectors on cables that are used to connect devices to one another. Sometimes, connectors are used without a cable to directly connect the device to another device, such as a charging station or a sound system.
As smart-phones, media players, health monitoring devices and other electronic devices become increasingly prevalent, consumers become more reliant on the connectors and cables required to connect these devices to other computing devices and electrical outlets. The devices, and therefore the connectors for the devices and their corresponding cables, remain with consumers throughout the day as they travel in and out of fitness centers, kitchens, offices, factories, automobiles, and many other places.
Many of these locations provide opportunities for exposure to chemicals that pose little or no risk to the consumer, but present a harsh environment for contacts on traditional electrical connectors. For example, connectors regularly come into contact with food, sweat, and other elements that corrode the materials that make up the connector contacts. For example, a cable may even be plugged into an electrical outlet while the connector at the other end is exposed to harsh chemicals, such as a spilled soda, resulting in even greater corrosion.
Contacts are made primarily of copper alloys, due to their advantageous electrical properties. However, copper alloys are also highly susceptible to corrosion. Because of this, contacts are often covered with a sulfumate nickel underplate. As used herein, sulfumate nickel means any nickel that contains at least 98% nickel sulfumate Ni(NH2SO3)2. The nickel underplate acts as a corrosion barrier and a wear barrier, because it is less corrosive and harder than the copper alloy that it covers. A gold layer is often placed on the outer layer in order to decrease contact resistivity. Diffusion of ions between the gold layer and the copper results in additional corrosion. The nickel underplate acts as a diffusion barrier, preventing the diffusion of gold ions from the outer gold layer into the copper alloy and vice versa. But nickel has inherent porosity. The thicker the nickel plating, the more likely pores will be created that can form a channel from the gold layer all the way to the copper alloy. Therefore, porosity defeats the diffusion resistance properties of nickel, because the channels formed between the gold layer and the copper alloy allow for the travel of ions between these layers.
The traditional contacts described above regularly survive industry standard tests for corrosion susceptibility, but these tests are directed to exposure to gases that encourage corrosion, and not the harsher chemicals described above. When consumer electronics and other electronic products are returned because of connector failures, it is common to see corrosion that can only be explained by exposure to food, sweat, or other chemicals that have a corrosive effect on connectors, but fall outside of the industry standard tests. In order to provide connectors that perform well in a typical environment in which consumer electronics are used, protection of the connectors from the chemicals found in these environments is desirable.
Embodiments relate to the use of a multi-layer nickel underplate on a contact for an electronic connector. According to one aspect, the multi-layer nickel underplate comprises a leveling nickel layer that is applied to a substrate material on the connector, such as copper. A layer of sulfumate nickel is formed over the leveling nickel, and a layer of high-phosphorous nickel is formed over the sulfumate nickel.
In one embodiment the multi-layer underplate consists of three layers where the sulfumate nickel layer is formed directly on the leveling nickel layer and the high-phosphorous nickel is formed directly on the sulfumate nickel layer. In an embodiment, a gold-plating is applied to the high-phosphorous nickel plating. In an embodiment, the multi-layer nickel underplate is applied to only a portion of the contact. The multi-layer nickel underplate is applied to the entire surface area of the contact in an embodiment.
In an embodiment, the thickness of the leveling nickel plating is between 10 and 150 microinches, the thickness of the sulfumate nickel plating is between 10 and 150 microinches, and the thickness of the high-phosphorous nickel plating is between 10 and 100 microinches. In one embodiment, the combined thickness of the multi-layer underplate is between 30 and 180 microinches. In an embodiment, the thickness of the sulfumate nickel layer is dependent on the thickness of the leveling nickel layer. For example, the sulfumate nickel layer may have a thickness that is between 80% to 120% of the thickness of the leveling nickel layer. In an embodiment, the thickness of the high-phosphorous nickel layer is dependent on the thickness of the leveling nickel layer and/or the sulfumate nickel layer. For example, the high-phosphorous nickel layer may have a thickness that is between 25% to 100% of the thickness of the sulfumate nickel layer.
According to another aspect, leveling nickel plating is applied using an electroplating solution comprising: between 20-40 oz/gal Nickel sulphate, NiSO46H2O; between 4-20 oz/gal Nickel chloride, NiCl26H2O; and between 4-7 oz/gal Boric acid, H3BO3. In an embodiment, the electroplating solution further comprises between 0.1-3 oz/gal of one or both of paratoluene sulfonamide and benzene sulphonic acid. In an embodiment, the electroplating solution further comprises between 0.0006-0.02 oz/gal of formaldehyde chloral hydrate and/or allyl sulfonic acid. In an embodiment, the electroplating solution comprises between 0.01-0.5 oz/gal of one or both of the group comprising: sodium allyl sulfonate and pyridinum propyl sulfonate.
According to another aspect, the roughness of the substrate is greater than the roughness of the leveling nickel surface.
Many electronic devices such as smart-phones, media players, and tablet computers have corresponding cables that facilitate battery charging and communication with other devices.
Contacts are designed to interface with other contacts when the connector is attached to another device. For example, when connector 110 is plugged into a USB “port,” the contacts for the USB port become coupled to the contacts for cable 100. This coupling effect allows electrical signals used for communication and electricity used for charging a device coupled to the other end of cable 100. Although USB connectors are discussed herein to illustrate one possible embodiment, other embodiments may be implemented on different types of connectors, such as fire wire connectors, thunderbird connectors, and other connectors for multimedia devices, computers, and smart-phones.
The portion of contact 200 that is designed to be coupled with a contact that is part of another connector or port is referred to herein as the “contact portion” 210. Nickel plating of the contact portion is often used as part of the preparation process, in order to provide corrosion resistance and durability. Electroplating is a widely used method of nickel plating. Nickel electroplating is performed by immersing the contact into an electrolyte solution. The contact is used as a cathode, and when the nickel anode is being dissolved into the electrolyte, nickel ions traveling through the solution are deposited on the surface of the contact.
In an embodiment, a multi-layer nickel underplate is deposited on connector contacts using electroplating techniques. In another embodiment, electroless nickel plating techniques may be used to apply the multi-layer nickel underplate.
Referring to
Referring to
In an embodiment, leveling nickel layer 320A is not applied directly to the substrate, but is applied to a conductive material that is first applied to the substrate. For example, a layer of high-phosphorous nickel or another type of nickel may be applied to the substrate before the application of the leveling nickel layer 320A. The other type of nickel may even be second type of leveling nickel, for a two-layer leveling combination. In an embodiment, conductive material may be applied between layers 320A and 320B, and/or between layers 320B and 320C.
The first layer, or leveling nickel layer 320A of the underplate is made up of 40 micro-inches of leveling nickel in an embodiment. In other embodiments, the leveling nickel layer ranges from 10 to 150 microinches. As used herein, “leveling nickel” means any nickel that includes one or more additives that increase the leveling characteristics of nickel. Leveling nickel reduces porosity and creates level and smooth surfaces. Leveling nickel is applied to the substrate material, which may be a copper alloy.
Because electrical current tends to be attracted to the peaks of materials, plating materials also tend to be attracted to peaks in the substrate material during the electroplating process. This results in the build-up of plating materials on the peaks of the substrate material, creating a rough surface. When nickel with increased leveling characteristics is applied to a substrate using an electroplating technique, the nickel displays an increased attraction to the valleys in the substrate, creating a leveling effect by filling in the valleys instead of building up the peaks of the substrate. Leveling nickel includes high-leveling nickel, which is commonly used for decorative purposes due to the brightening effect resulting from the level distribution of nickel during the plating process.
Leveling nickel also includes any nickel which, when applied to a material, causes the resulting surface to be smoother than the surface of the material to which the nickel was applied. For example, optical measurement methods such as interference, path length, optical penetration, or resolution of focus may be used to measure roughness. A low coherence interferometer may be used to split a beam of light in the infrared range into two separate beams. One beam is directed at the surface and the other is directed at a mirror in the inferometer's reference arm. The probe receives and recombines the reflected light from the sample and reference arms and records the resulting interference. Based on this, the inferometer can determine the surface shape, roughness and waviness.
The additives used to achieve the leveling effect in leveling nickel are sometimes referred to as brightening agents or complexing agents. These additives may include ascorbic acid, isoascorbic acid, citrate, gluconate, tartrate, sulfo-oxygen, and other organic additives and brightening agents used to increase the brightness and leveling effects of nickel used for electroplating. These additives may also include secondary brighteners that work synergistically with other additives. Secondary additives may include 2-butyne-1, 4-diol, the general class of acetylenic alcohols, or coumarins. Although specific additives have been discussed herein, nickel that includes any additive that increases the leveling characteristics of nickel is considered leveling nickel, and may be used in an embodiment.
Due to simplicity and low cost, a popular nickel electroplating solution is known as the Watts solution. An example of a Watts solution that may be used in an embodiment includes the following composition ranges:
Nickel sulphate, NiSO46H2O: 20-40 oz/gal
Nickel chloride, NiCl26H2O: 4-20 oz/gal
Boric acid, H3BO3: 4-7 oz/gal
Agents such as paratoluene sulfonamide, benzene sulphonic acid can be added in concentration of 0.1-3 oz/gal (0.75-23 g/l) to achieve a leveling effect in an embodiment. These agents contain sulfur, and provide for a uniform plating. Agents such as formaldehyde chloral hydrate and allyl sulfonic acid can be added in concentration of 0.0006-0.02 oz/gal (0.0045-0.15 g/l) to achieve a leveling effect in an embodiment. These agents are secondary brightners, and produce in combination with other agents, a very smooth surface. Other agents such as sodium allyl sulfonate and pyridinum propyl sulfonate can be added to the solution in concentration of 0.01-0.5 oz/gal (0.075-3.8 g/l) to achieve a leveling effect in an embodiment.
The second layer, or the sulfumate nickel layer 320B, of the underplate is made up of 40 micro-inches of standard sulfumate nickel in an embodiment. In other embodiments, the sulfumate nickel layer 320B has a thickness between 5-150 microinches. Sulfumate nickel is very hard, and represents an inexpensive way to add strength and average corrosion resistance to the contact at a relatively low stress level. The porosity of the sulfumate nickel is mitigated by the leveling nickel layer, avoiding the main weakness of the traditional single-layer underplate.
The third layer of the underplate, or the high-phosphorous nickel layer 320C, is made up of 20 micro-inches of high-phosphorous nickel in an embodiment. In other embodiments, the high-phosphorous nickel layer 320C has a thickness between 5-100 microinches. As used herein, high-phosphorous nickel means any nickel that contains at least 4.5% phosphorous. However, high-phosphorous nickel does not commonly exceed 15% phosphorous. High-phosphorous nickel is one of the least corrosive of all nickel compounds, and acts as a sealer for the other layers.
In an embodiment, only the contact portion 210 of contact 200 is expected to come into contact with other contacts. Therefore, other plating materials or material quantities may be used on other portions of contact 200. For example, contact portion 210 includes a surface plate of 30 microinches or more of gold in an embodiment. Other portions, also described herein as non-contact portions, of contact may only have a thinner coating of gold applied, because gold is expensive, and non-contact portions of contact 200 are unlikely to achieve any additional advantage by having a thicker layer of gold plating.
To prove the corrosion resistance properties of the multi-layer nickel underplating, multiple embodiments were tested. The following equipment was used:
Potentiostat: Gamry PCI4/300 with Framework/DC105 software
Reference Electrode: Saturated calomel electrode (SCE)
Tempurature Control: Temperature-controlled hot plate and water bath
Reagents included a) Water: Reagent grade distilled, deionized water; ASTM D 1193, Type II; and b) Test solution: Phosphate-buffered saline (PBS) per ASTM F2129-08. Sigma-Aldritch. For preparation, all 5 pins of a micro-USB connector were shorted together on the solder side and connected to the test lead. Silicone sealant was used to cover all exposed metal surfaces except the pin mating ends.
For each of the following tests, a USB connector was submerged in the solution, and the open-circuit potential was measured for five minutes before the application of 0.7V versus the SCE. A measurement of electrical current was taken every 5 seconds. The test was performed at room temperature.
A first test was performed on a connector with contacts having a copper substrate, where the contact area of the copper substrate was plated with a 80 microinch sulfumate nickel plating, which was in turn plated with 30 microinches of gold.
A second test was performed on a connector with contacts having a copper substrate, where the contact area of the copper substrate was plated with a multi-layer nickel underplating. The multi-layer nickel underplating was plated with 30 microinches of gold. The multi-layer nickel underplating that was used in the second test included 40 microinches of leveling nickel plating, 40 microinches of sulfumate nickel plating, and 20 microinches of high-phosphorous nickel plating.
A third test was performed on a connector with contacts having a copper substrate, where the contact area of the copper substrate was plated with a multi-layer nickel underplating. The multi-layer nickel underplating was plated with 30 microinches of gold. The multi-layer nickel underplating that was used in the third test included 80 microinches of leveling nickel plating, 40 microinches of sulfumate nickel plating, and 40 microinches of high-phosphorous nickel plating.
The results of the tests are charted in
It is evident from the chart in
In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the invention, and what is intended by the applicants to be the scope of the invention, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.
