PATENT DOCUMENT

Publication Number: US-10553352-B2
Application Number: US-201715464077-A
Country: US
Kind Code: B2

Title: Corrosion resistant magnet assembly

Abstract:
Embodiments of the disclosure pertain to methods of plating magnets with a stack of layers such that the resulting magnet assembly has improved corrosion resistance. Embodiments of the disclosure are also directed to magnet assemblies formed by such methods. Some embodiments include a High Phosphorus Electroless Nickel (HiPEN) layer with Phosphorus content greater than 11% by weight.

Claims:
What is claimed is: 
     
       1. A receiver magnet assembly comprising:
 a magnet; and 
 a stack of layers disposed over the magnet comprising, in order:
 a barrier metal layer; 
 a catalyst layer comprising palladium or semi-bright nickel; and 
 a High Phosphorus Electroless Nickel (HiPEN) layer having Phosphorus content that is greater than 11% by weight, wherein the HiPEN layer is the outermost layer of the receiver magnet. 
 
 
     
     
       2. The receiver magnet assembly of  claim 1  further comprising a stress separation layer disposed between the barrier metal layer and the catalyst layer. 
     
     
       3. The receiver magnet assembly of  claim 2 , wherein the barrier metal layer comprises a first transition metal, and the stress separation layer comprises a second transition metal different from the first transition metal. 
     
     
       4. The receiver magnet assembly of  claim 3 , wherein the first transition metal is zinc, the second transition metal is copper. 
     
     
       5. The receiver magnet assembly of  claim 1 , wherein the magnet is a rare earth magnet. 
     
     
       6. The receiver magnet assembly of  claim 1 , wherein the catalyst layer comprises a monolayer of palladium. 
     
     
       7. The receiver magnet assembly of  claim 1 , wherein the stack of layers encloses the magnet. 
     
     
       8. The receiver magnet assembly of  claim 1 , wherein the catalyst layer increases the deposition rate of the HiPEN layer. 
     
     
       9. A receiver magnet assembly, comprising:
 a magnet; and 
 a stack of layers disposed over the magnet comprising, in order:
 a barrier metal layer; 
 a metal alloy layer; 
 a metallic passivation layer comprising palladium or semi-bright nickel; and 
 a High Phosphorus Electroless Nickel (HiPEN) layer having Phosphorus content that is greater than 11% by weight, wherein the HiPEN layer is the outermost layer of the receiver magnet. 
 
 
     
     
       10. The receiver magnet assembly of  claim 9  wherein the barrier metal layer comprises nickel, the metal alloy layer comprises nickel and zinc, and the metallic passivation layer comprises chromium. 
     
     
       11. The receiver magnet assembly of  claim 9 , wherein the metallic passivation layer increases a scratch resistance of the stack of layers. 
     
     
       12. The receiver magnet assembly of  claim 9  wherein the magnet is a rare earth magnet. 
     
     
       13. The receiver magnet assembly of  claim 9 , wherein the stack of layers encloses the magnet. 
     
     
       14. The receiver magnet assembly of  claim 9 , wherein the barrier metal layer comprises a first transition metal and the stack of layers further comprises a stress separation layer comprising a second transition metal different from the first transition metal. 
     
     
       15. A receiver magnet assembly comprising:
 a magnet; and 
 a stack of layers disposed over the magnet comprising, in order:
 a first metallic layer; 
 a second metallic layer different from the first metallic layer, the second metallic layer serving to reduce stress-induced corrosion; 
 a catalyst layer comprising palladium or semi-bright nickel; and 
 a High Phosphorus Electroless Nickel (HiPEN) layer having Phosphorus content that is greater than 11% by weight, wherein the HiPEN layer forms an exterior surface of the magnet assembly. 
 
 
     
     
       16. The receiver magnet assembly of  claim 15  wherein the first metallic layer comprises nickel, the second metallic layer comprises copper, and the catalyst layer comprises semi-bright nickel. 
     
     
       17. The receiver magnet assembly of  claim 15  wherein the magnet is a rare earth magnet. 
     
     
       18. The receiver magnet assembly of  claim 15  wherein the stack of layers further comprises a metallic passivation layer that comprises chromium. 
     
     
       19. The receiver magnet assembly of  claim 15 ,
 wherein the receiver magnet is mounted in a yoke of an acoustic receiver. 
 
     
     
       20. The receiver magnet assembly of  claim 15 , wherein the catalyst layer increases the deposition rate of the HiPEN layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/310,453, filed Mar. 18, 2016, and entitled “CORROSION RESISTANT MAGNET ASSEMBLY AND METHOD OF MAKING THE SAME”, which is herein incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to corrosion resistant coatings. 
     BACKGROUND 
     Receiver magnets are used in phone receivers, including in mobile phone receivers. The receiver magnet can be used to drive the coils to make the receiver work, thereby operating a speaker in the phone. Receiver magnets can be prone to corrosion that can result in degraded acoustic performance, for example, because of changed size and properties of the magnet itself, and/or because of smaller particles formed as the magnet corrodes. These particles can interfere with other components in the receiver, such as the coils, as they move. This can, for example, produce an undesirable “hissing” noise at the speakers or otherwise degrade audio quality. Hence, there is a need for receiver magnets to be corrosion resistant. Other magnets including rare earth magnets, used in acoustic or other applications, can also benefit from corrosion resistant properties. Corrosion resistant coatings can also be useful in other applications such as electrical contacts. 
     SUMMARY 
     Embodiments of the disclosure pertain to methods of plating magnets with a stack of layers such that the resulting magnet assembly has improved corrosion resistance. While some embodiments of the disclosure are particularly useful for improving corrosion resistance of receiver magnets while maintaining the receiver acoustic and drop performance, other embodiments can beneficially improve the corrosion resistance of magnets used in other applications or improve the corrosion resistance of other structures, such as electrical contacts. Embodiments also pertain to assemblies formed by such methods. 
     In some embodiments, a multi-layer stack of different materials is formed over a rare earth magnet (e.g. NdFeB) core. The multi-layer stack can include one or more layers having properties tailored to act as a barrier layer, a catalyst, a scratch protection layer, a passivation layer, and/or a corrosion resistant layer. The multi-layer stack can enclose the rare earth magnet core, thereby protecting all surfaces of the rare earth magnet core. 
     Some embodiments of the disclosure are directed to a receiver magnet assembly that includes a magnet and a stack of layers disposed over the magnet. Embodiments are also directed to methods of making such magnet assemblies. According to some embodiments, the stack of layers includes, in order: a barrier metal layer, a catalyst layer, and a High Phosphorus Electroless Nickel (HiPEN) layer, where the Phosphorus content in the HiPEN layer is greater than 11% by weight. 
     In some embodiments, the stack of layers can further include a stress separation layer disposed between the barrier metal layer and the catalyst layer. As examples, the barrier metal layer can comprise a first transition metal, and the stress separation layer can comprise a second transition metal. In particular examples, the first transition metal can be zinc and the second transition metal can comprise copper. The magnet can comprise a rare earth metal, and in some embodiments can take the form of a NdFeB magnet. In some example, the catalyst layer can comprise palladium. 
     Some embodiments of the disclosure are directed to a receiver magnet assembly include a magnet having a stack of layers disposed over the magnet and at methods of making such magnet assemblies. According to some embodiments, the stack of layers disposed over the magnet can include, in order: a barrier metal layer, a metal alloy layer, and a metallic passivation layer. As examples, the barrier metal layer can comprise nickel, the metal alloy layer can comprise an alloy of nickel and zinc, and the metallic passivation layer can comprise chromium. 
     According to some embodiments, the stack of layers can include, in order: a first protective metallic layer, a second metallic layer different from the first protective metallic layer, the second metallic layer serving to reduce stress-induced corrosion, a catalyst layer, and a High Phosphorus Electroless Nickel (HiPEN) layer, wherein the Phosphorus content in the HiPEN layer is greater than 11% by weight. As examples, the first protective metallic layer can comprises nickel, the second metallic layer can comprise copper, and the catalyst layer can comprise semi-bright nickel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified exploded view of an example receiver showing the location of a receiver magnet; 
         FIG. 2  is an illustration of a corroded receiver magnet displaced from its yoke; 
         FIG. 3A  is a simplified cross-sectional view of a magnet assembly with a nickel-copper-nickel stack formed over the magnet; 
         FIG. 3B  is a simplified cross-sectional view of a magnet assembly with a zinc layer and a chromium passivation layer formed over the magnet; 
         FIG. 4  is a flowchart of an example method of forming a corrosion-resistant magnet assembly according to some embodiments of the disclosure; 
         FIG. 5  is a simplified cross-sectional view of a magnet assembly with a stack of layers over a magnet, according to some embodiments of the disclosure; 
         FIG. 6  is a flowchart of an example method of forming a corrosion-resistant magnet assembly according to some embodiments of the disclosure; 
         FIG. 7  is a simplified cross-sectional view of a magnet assembly with a stack of layers over a magnet, according to some embodiments of the disclosure; 
         FIG. 8  is a flowchart of an example method of forming a corrosion-resistant magnet assembly according to some embodiments of the disclosure; 
         FIG. 9  is a simplified cross-sectional view of a magnet assembly with a stack of layers over a magnet, according to some embodiments of the disclosure; 
         FIG. 10  is a flowchart of an example method of forming a corrosion-resistant magnet assembly according to some embodiments of the disclosure; 
         FIG. 11  is a simplified cross-sectional view of a magnet assembly with a stack of layers over a magnet, according to some embodiments of the disclosure; 
         FIG. 12  is a cross section micrograph of the stack of layers from a magnet assembly formed according to embodiments of the disclosure; and 
         FIG. 13  is a simplified cross-section of a corrosion-resistant electrical contact, formed according to embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the disclosure pertain to methods of plating magnets with a stack of layers such that the resulting magnet assembly has improved corrosion resistance. The magnet in a receiver can corrode, causing total harmonic distortion (THD) or functional receiver failures. While some embodiments of the disclosure are particularly useful for improving corrosion resistance of receiver magnets while maintaining the receiver acoustic and drop performance, other embodiments can beneficially improve the corrosion resistance of magnets used in other applications or improve the corrosion resistance of other structures, such as electrical contacts. Embodiments also pertain to the assemblies formed by such methods themselves. 
     In some embodiments, a multi-layer stack of different materials is formed over a rare earth magnet (e.g. NdFeB) core. Although the explanation in the specification has been provided with NdFeB magnets as an example, methods described can be applicable to other kinds of magnets as well. The multi-layer stack can include one or more layers serving one or more functions. For example, layers can have properties tailored to act as a barrier layer, a catalyst, a scratch protection layer, a passivation layer, and/or a corrosion resistant layer. 
     Embodiments of the disclosure can operate with one or more acoustic receivers that can be used, for example in a speaker of a mobile phone.  FIG. 1  shows an exploded view of an exemplary acoustic receiver  100  illustrating the location of a magnet  145  within acoustic receiver  100 . 
     As shown in  FIG. 1 , acoustic receiver  100  can include various components, such as a diaphragm  130 , a voice coil  135 , a magnet plate  140 , a magnet  145 , a yoke  170 , springs  175 , and connectors  180 . Magnet  145 , housed inside yoke  170  in some embodiments, can drive voice coils  135  to make receiver  100  work. In some embodiments, magnet  145  can comprise a rare earth magnet. For example, magnet  145  can be a neodymium-based magnet such as Nd 2 Fe 14 B, sometimes abbreviated NIB. Although explained here in the context of a receiver magnet, embodiments of the invention based on neodymium-based magnets can be used in other applications such as hard drives, cordless tools, and electric motors. 
     Neodymium-based magnets undergo undesirable amounts of corrosion when exposed to the atmosphere. Such corrosion can be rapid and can degrade the performance of the device they are part of, in this example, the receiver (and hence the speaker). As the magnet corrodes, it can lose mass and hence change in shape and size, thereby affecting the properties and performance of the speakers. When the volume of the magnet decreases, the amount of magnetic flux created by the magnet decreases, and can fall below the amount of magnetic flux for which the receiver was designed. This can adversely affect performance. 
     Furthermore, corrosion of the magnet can generate small particles which can end up interfering with other components in the receiver such as vibrating coils that go around the magnet (e.g., voice coil  135 ). These particles can make contact with the coils and create a rubbing or “hissing” noise. 
       FIG. 2  illustrates an example of a corroded magnet  210  of an acoustic receiver. As shown in  FIG. 2 , corrosion at the surfaces of magnet  210  is particularly clear along at corroded side surface  230  of magnet  210 . Corroded side surface  230  can appear brownish-red because of the iron oxide buildup on the exterior of the magnet. The corrosion can also cause small particles to be formed around magnet  210 . Magnet  210  can also lose mass and get displaced from yoke  220  as shown in  FIG. 2 , leaving gaps between the edge of magnet  210  and yoke  220 , as illustrated by gap  240 . 
     In general, corrosion of neodymium-based magnets can be accelerated in the presence of heat, moisture, and acidic environments. For the purposes of studying corrosion behavior of the magnets, corrosion can be accelerated through heat soak, salt spray, acetic acid heat soak, etc. 
     One way to reduce corrosion of magnets is through the use of one or more protective coatings formed over the magnet. Protective coatings can be of varying thicknesses and can take the form of single layer or multi-layer stacks. Such layers can be applied using several techniques including brush painting, dipping, spraying, electrophoresis, physical vapor deposition, ion vapor deposition, electroplating, electroless plating, and other suitable methods. 
     Two examples of multi-layer layer stacks formed on a magnet  310  that impart some amount of corrosion resistance are shown in  FIGS. 3A and 3B , which are simplified cross-sectional views of a magnet assembly  300  and a magnet assembly  350 , respectively. Referring to  FIG. 3A , magnet assembly  300  includes a magnet  310 , a first nickel layer  320  formed over the magnet, a copper layer  330  formed over first nickel layer  320 , and a second nickel layer  340  formed over copper layer  330 . In embodiments, the thickness of first nickel layer  320  can be between 2 and 6 μm, the thickness of copper layer  330  can be between 2 and 5 μm, and the thickness of second nickel layer  340  can be between 2 and 6 μm. The three layers can be applied using electroplating and other suitable methods. Although nickel provides corrosion resistance, nickel is ferro-magnetic, interferes with the magnetic flux that magnet  310  produces, and can end up causing ‘magnetic shorting’ when the flux generated magnet  310  ends up getting stuck within first nickel layer  320 . 
     Referring to  FIG. 3B , magnet assembly  350  includes a magnet  310 , a zinc layer  360 , and a chromium passivation layer  370 . Zinc layer  360  provides an initial layer of corrosion resistance to underlying magnet  310 , and zinc, being non-magnetic, provides the advantage of not interfering with the magnetic flux generated by magnet  310 . However, the corrosion resistance provided by zinc can prove to be inadequate under some conditions. To further improve corrosion resistance of magnet assembly  350 , chromium passivation layer  370  is formed over zinc layer  360 . In embodiments, the thickness of zinc layer  340  can be between 2 and 10 μm. Layers  360  and  370  can be applied using electroplating and other suitable methods. 
     In some embodiments, a high phosphorus nickel formed by electroless plating, or High Phosphorus Electroless Nickel (HiPEN) can be used for plating a magnet to improve the corrosion resistance of the magnet assembly. HiPEN offers the advantage of being non-magnetic because of its high phosphorus content, which allows HiPEN to impart corrosion resistance while simultaneously having minimal impact on magnetic performance. Preferably, a phosphorus content of greater than 11 percent by weight renders the HiPEN non-magnetic with a magnetic permeability of close to 1. The high phosphorus content also changes the microstructure of the nickel, making it more amorphous. 
     According to some embodiments of the disclosure, a layer of HiPEN can be formed over a magnet to make the assembly corrosion resistant. However, the process of electroless nickel plating can be slow. During the electroless nickel plating process, electroless nickel can get trapped inside cracks near the surface region of the NdFeB magnet causing blistering and corrosion. To reduce or prevent such blistering and/or corrosion, a barrier layer can be formed between the magnet and the electroless nickel layer as described below in conjunction with  FIGS. 4 and 5 . 
       FIG. 4  and  FIG. 5  are directed to a method of forming a magnet assembly and the magnet assembly formed by such a method respectively, according to some embodiments of the invention.  FIG. 4  is a flowchart illustrating an example of a process  400  that can be used to make magnet assembly  500  of  FIG. 5 , according to some embodiments.  FIG. 5  is a magnet assembly formed by process  400 , although processes other than process  400  can potentially be used to form magnet assembly  500 . References will simultaneously be made to elements from  FIG. 4  and  FIG. 5  in the description below. 
     At block  410 , process  400  includes forming a barrier metal layer  520  over a magnet  510 . In some embodiments, barrier metal layer  520  can be or can include zinc. Zinc is diamagnetic and thus does not affect the magnetic flux from magnet  510 . In other embodiments, barrier metal layer  520  can include other transition metals, such as aluminum copper, nickel, or cobalt. During the subsequent electroless nickel plating process (described further below with reference to block  430 ), barrier metal layer  520  can prevent the electroless nickel from attacking and corroding magnet  510 . The thickness of barrier metal layer  520  can be tailored to ensure that subsequently deposited electroless nickel does not come in contact with the magnet. In some embodiments, the thickness of barrier metal layer  520  can be 2-4 μm. 
     Deposition of HiPEN on barrier metal layer  520  can be slow, thereby posing a risk of the HiPEN corroding barrier metal layer  520  during the HiPEN deposition process and eventually coming in contact with magnet  510 . Such a risk can be reduced by using a thin catalyst layer over barrier metal layer  520  to speed up HiPEN deposition. 
     At block  420 , process  400  includes forming a catalyst layer  530  over barrier metal layer  520 . In examples, catalyst layer  530  can include a monolayer of palladium, formed by a palladium dip. Other examples of catalyst layer  530  can include semi-bright nickel. Catalyst layer  530  can increase the rate of subsequent HiPEN deposition, and thereby reduce the risk of HiPEN coming in contact with magnet  510  by corroding through barrier metal layer  520  during HiPEN deposition. 
     At block  430 , process  400  includes forming a HiPEN layer  540  by electroless nickel plating. Unlike electroplating, in electroless nickel plating, it is not necessary to pass an electric current through the solution to form a deposit. Advantages of the Electroless Nickel (EN) process can include uniform deposition, and the ability to provide different kinds of finishes such as matte, bright, rough, or smooth. A relatively rough EN can help with adhesion to the yoke when the magnet assembly is sealed to the yoke using a glue. In some embodiments, the thickness of HiPEN layer  540  can be between 2 and 9 μm. 
     Layers formed over the magnet can be thin—on the order of a few microns—and hence prone to scratching from handling, both during and after the plating process. If the layers are very thin, even minor scratching can expose the underlying magnet. High volume production invariably involves handling and can cause scratching. A scratch resistant layer in the stack can be beneficial, for example, in such situations when used as a top surface. While the EN layer itself provides the advantage of scratch resistance when used as the top layer, a stress separation layer can be used to alleviate stress between the magnet and the outer layers. 
       FIG. 6  and  FIG. 7  are directed to a method of forming a magnet assembly and the magnet assembly formed by such a method respectively, according to some embodiments of the disclosure.  FIG. 6  is a flowchart illustrating an example of a process  600  that can be used to make magnet assembly  700  of  FIG. 7 , according to some embodiments.  FIG. 7  is a magnet assembly formed by process  600 , although processes other than process  600  can potentially be used to form magnet assembly  700 . References will simultaneously be made to elements from  FIG. 6  and  FIG. 7  in the description below. 
     At block  610 , process  600  includes forming a barrier metal layer  720  over a magnet  710 . In some embodiments, barrier metal layer  720  can be or can include zinc. Zinc is diamagnetic and thus does not affect the magnetic flux from magnet  710 . In other embodiments, barrier metal layer  720  can include other transition metals, such as aluminum, copper, nickel, and cobalt. The thickness of barrier metal layer  720  can be tailored to ensure that subsequently deposited electroless nickel does not come in contact with the magnet. In some embodiments, the thickness of barrier metal layer  720  can be 2-4 μm. 
     At block  620 , process  600  includes forming a stress separation layer  730 . In some embodiments, stress separation layer  730  can be or can include copper. Copper is also non-magnetic and does not interfere with the magnetic flux. In other examples, stress separation layer  730  can include other hard transition metals. The thickness of stress separation layer  730  can be tailored to ensure that the stack has an optimum thickness for alleviating stress. In some embodiments, the thickness of stress separation layer  730  can be 2-4 μm. Stress separation layer  730  can make magnet assembly  700  more suitable for high volume production. 
     At block  630 , process  600  includes forming a catalyst layer  740  over stress separation layer  730 . In examples, catalyst layer  740  can include a monolayer of palladium formed by a palladium dip. Other examples of catalyst layer  530  can include semi-bright nickel. Catalyst layer  740  can increase the rate of subsequent HiPEN deposition, and reduce the risk of HiPEN coming in contact with magnet  710 . 
     At block  640 , process  600  includes forming a HiPEN layer  750  by electroless nickel plating. Unlike electroplating, in electroless nickel plating, it is not necessary to pass an electric current through the solution to form a deposit. Advantages of the EN process can include uniform deposition, and ability to provide different kinds of finishes such as matte, bright, rough, or smooth. In some embodiments, the thickness of HiPEN layer  750  can be between 6-9 μm. 
       FIG. 8  and  FIG. 9  are directed to a method of forming a magnet assembly and the magnet assembly formed by such a method respectively, according to some embodiments of the disclosure.  FIG. 8  is a flowchart illustrating an example of a process  800  that can be used to make magnet assembly  900  of  FIG. 9 , according to some embodiments. Process  800  can be used in mass production of plating stacks.  FIG. 9  is a magnet assembly formed by process  800 , although processes other than process  800  can potentially be used to form magnet assembly  900 . References will simultaneously be made to elements from  FIG. 8  and  FIG. 9  in the description below. 
     At block  810 , process  800  includes forming a first protective metallic layer  920  over a magnet  910 . First protective metallic layer  920  can be formed using several techniques such as dipping, spraying, and other suitable methods. In some embodiments, first protective metallic layer  920  can be or can include nickel. Nickel diffuses into the boundaries of the magnet surface region holds the magnet&#39;s structure, and prevents cracks from propagating. In some embodiments, the thickness of first protective metallic layer  920  can be between 3 and 4 μm. 
     At block  820 , process  800  includes forming a second metallic layer  930 . Second metallic layer  930  can help to reduce stress extending from the substrate, thereby minimizing stress-induced corrosion. Second metallic layer  930  can also prevent further magnetic shorting between first protective metallic layer  920 , and layers deposited over second metallic layer  930 . In some embodiments, second metallic layer  930  can be or can include copper. In some embodiments, the thickness of second metallic layer  930  can be 2-4 μm. 
     At block  830 , process  800  includes forming a catalyst layer  940 . In examples, catalyst layer  940  can include semi-bright nickel. In some embodiments, semi-bright nickel can be used in place of, or in addition to, the more expensive palladium dip. Semi-bright nickel can have less grain refiner, which can result in larger nickel grains. This can create a rougher surface that promotes better plating adhesion. In some embodiments, ˜1 μm of semi-bright nickel can be used. Catalyst layer  940  can increase the rate of subsequent HiPEN deposition. 
     At block  840 , process  800  includes forming a HiPEN layer  950  by electroless nickel plating. Unlike electroplating, in electroless nickel plating, it is not necessary to pass an electric current through the solution to form a deposit. Advantages of the EN process can include uniform deposition, corrosion and scratch resistance, and ability to provide different kinds of finishes such as matte, bright, rough, or smooth. When compared to several other materials, a relatively thinner EN layer can provide the required corrosion and scratch resistance. This can allow for a bigger magnet for the same overall thickness of the magnet assembly. In some embodiments, the thickness of HiPEN layer  950  can be between 2-3 μm. 
     In some embodiments, a metal alloy layer, such as zinc-nickel alloy layer, can be used in the stack for corrosion resistance. A metal alloy layer can provide the advantage of easy manufacturability. 
       FIG. 10  and  FIG. 11  are directed to a method of forming a magnet assembly and the magnet assembly formed by such a method respectively, according to some embodiments of the disclosure.  FIG. 10  is a flowchart illustrating an example of a process  1000  that can be used to make magnet assembly  1100  of  FIG. 11 , according to some embodiments.  FIG. 11  is a magnet assembly formed by process  1000 , although processes other than process  1000  can potentially be used to form magnet assembly  1100 . References will simultaneously be made to elements from  FIG. 10  and  FIG. 11  in the description below. 
     At block  1010 , process  1000  includes forming a barrier metal layer  1120  over a magnet  1110 . Barrier metal layer  1120  can be formed using several techniques such as dipping, spraying, and other suitable methods. In some embodiments, barrier metal layer  1120  can be or can include zinc. In some embodiments, the thickness of barrier metal layer  1120  can be between 2 and 4 μm. 
     At block  1020 , process  1000  includes forming a metal alloy layer  1130 . In some embodiments, metal alloy layer  1130  can include an alloy of zinc and nickel. In such embodiments, the metal alloy layer can have the combined advantages of corrosion resistance from nickel and diamagnetism from zinc. The percentage of nickel and zinc in such an alloy can be tailored based on the desired properties. For example, the percentage of zinc by weight can be between 3 and 30%. In some embodiments, the alloy of zinc and nickel can be electroplated using a plating solution of zinc and nickel ions. In some embodiments, the thickness of metal alloy layer  1130  can be 8-12 μm. 
     At block  1030 , process  1000  includes forming a passivation layer  1140 . In examples, passivation layer  1140  can include metallic chromium. 
       FIG. 12  is a Scanning Electron Microscope cross-section  1200  of the tack of layers from a magnet assembly formed according to some embodiments of the disclosure. The magnet assembly shown in  FIG. 12  can be formed according to methods of  FIG. 6 . Cross-section  1200  depicts a magnet  1210 , a barrier metal layer (zinc)  1220 , a stress separation layer (copper)  1230 , and a HiPEN layer  1240 . 
     Methods described above can be used in several components in computing and other devices where magnets are used. Examples of such components can include audio receivers, speakers, cameras, wireless chargers, wearable devices, and other suitable methods. Methods described above and magnet assemblies formed by such methods can impart significant corrosion resistance and prevent various kinds of failures in the components. 
     In some embodiments, methods and systems as described above can be used to form corrosion-resistant features that do not include magnets. For example, methods and apparatuses described above can be used for form corrosion-resistant electrical contacts. Such contacts can be used in consumer electronic equipment such as smart phones, tablets, and laptop computers. In some examples, a contact made of a copper-alloy such as phosphor bronze can be clad with a Precious Metal Alloy (PMA). The PMA can further be coated with a corrosion-resistant stack, such as stacks formed on a magnet described above with reference to  FIGS. 4-11 . 
       FIG. 13  is a simplified cross-section of a corrosion-resistant contact  1300  formed according to some embodiments. As shown in  FIG. 13 , contact body  1360  can be made of a metal or metal alloy such as copper or phosphor bronze. Contact  1300  makes contact to substrate  1350  in the contact area  1360 , and is electrically separated from adjacent features by a dielectric  1340 . In some embodiments, dielectric  1340  can be an air gap. On the side of contact  1300  that is exposed to the environment, a layer of Precious Metal Alloy (PMA)  1330  is formed. In some embodiments, PMA layer  1330  can include Paliney 7, a palladium, silver age-hardenable alloy that contains 10% gold and 10% platinum having a high resistance to corrosion and tarnish while providing the mechanical properties of Beryllium Copper. Over PMA layer  1330 , contact  1300  includes a corrosion resistant layer  1320 . In some embodiments, corrosion resistant layer can be made of a stack of layers. In one example, the stack of layers can include layers  520 ,  530 , and  540  of  FIG. 5 , in that order, with layer  520  disposed nearest to PMA layer  1330 . In another example, the stack of layers can include layers  720 ,  730 ,  740 , and  750  of  FIG. 7  in that order, with layer  720  disposed nearest PMA layer  1330 . In yet another example, the stack of layers can include layers  920 ,  930 ,  940 , and  950  of  FIG. 9  in that order, with layer  920  disposed nearest to PMA layer  1330 . In yet another example, the stack of layers can include layers  1120 ,  1130 , and  1140  of  FIG. 11  in that order, with layer  1120  disposed nearest to PMA layer  1330 . Processes such as those described in  FIGS. 4, 6, 8, 10  can be used to form layers of corrosion resistant layer  1330 . 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. For example, while several specific embodiments of the disclosure described above use neodymium-based receiver magnets, the disclosure is not limited to any particular kind of magnet. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170320
Publication Date: 20200204
Grant Date: 20200204
Priority Date: 20160318
Inventors: KWOK, WAI MAN RAYMUND
WAH, MELISSA
Assignee: APPLE INC
CPC Classifications: [{"code": "H01F27/23", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/0221", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F7/0221", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F7/0221", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F41/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/23", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R9/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2209/024", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 59856219