JPH07506773A - Medium temperature diffusion bonding - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Medium temperature diffusion bonding To Tsui a! Wataru TECHNICAL FIELD The present invention relates to joining and bonding articles, and more particularly to diffusion bonding. (welding) method.

There is a great need to mechanically, electrically or thermally connect articles or parts/components to each other. It occurs in a wide range of situations and many techniques have been developed. e.g. microelectronic devices In the manufacture of.

Connect terminals mechanically and/or electrically, or It is often necessary to mechanically join the structures. The joining is , must be done without damaging already existing microelectronic devices. No.

The most common requirements for such junctions in microelectronic devices The approach is to solder the parts together. In soldering, fusion Provide a pure metal or alloy with a low point at the location to be joined. Lead-tin, lead-indium aluminum and indium solders are widely used. Lead-tin solder is a hardware Familiar solders available at Tor; other solders are for more specialized applications. It was made in. Melt the solder and surrounding area to be joined. It is heated to a sufficient temperature and allowed to flow over the surfaces to be joined. Stop heating and remove parts. to cool down. As the parts cool, the solder solidifies and joins the parts together.

Although soldering is widely used, it has drawbacks in some applications. before the solder melts to wet it and allow it to flow over the surfaces to be joined. It is usually necessary to use a flux to clean the surfaces to be bonded. Hula Oxides are often corrosive compositions that clean surfaces, but they also clean micro- Leaves residues that can cause long-term damage to electronic components and does not damage surfaces to be joined. Etch the surface with acid before starting soldering to improve solder adhesion. It may also be necessary to The acid used for etching is similarly May result in damage to the device. In addition, the micro- Low temperature solders suitable for electronic applications are unknown. To achieve good solder joints requires careful process control, including the use of precise temperature and atmospheric conditions. . After careful selection of solder, proper surface preparation of the parts to be joined, and precision Even with advanced process controls, gaps and holes that significantly reduce strength are May be present at the final solder joint.

Soldering is expected to be a viable joining technique for many applications. other In applications, these drawbacks make this technology unsatisfactory. So Improved joining techniques that can replace soldering in applications such as The present invention satisfies this need and also provides related advantages. This is what we are trying to provide.

Supervised by i Tsui Q The present invention provides a joining technology for joining two members/components. Ru. This technology is of particular interest in the microelectronic industry, but more The 0-piece method, which has wide applicability, is entirely in a solid state and can be used for parts and materials. During the bonding process, neither the bonding material nor the bonding material is melted during the process. No ching or flux required.

Process control requires only temperature control, which is usually very accurate. It is certainly possible. The preferred maximum process temperature is is acceptable for many microelectronic devices that are themselves damaged by It's in the heating range. The final bond is in tension and creep.

much more than that achieved by low temperature solder that is melted during the traditional bonding process. strong. The method of the invention requires the ability to press the surfaces to be joined; Applicability is limited to situations where pressing is possible and permissible.

According to the invention, the method for joining two parts includes a first part to be joined; providing a first bonding surface on the material. This first bonding surface is connected to the first material. a first region of the material; and overlying the first region of the first material. ) and includes a first layer of a second material having a different composition than the first material. No. The second material forms an adhesive coating on the first material and is heated to about 125°C. It is resistant to oxidation at temperatures of about 250°C. This second material is about 125 with negligible solid solubility in the first material at temperatures below about 125°C has an increasing finite solid solubility in the first material at temperatures above . second The material includes a sufficient amount of material in the first material to bond the first material and the second material together. Interdiffusion from about 125°C to about 250°C Achieved at a temperature of The method of the present invention further includes applying a second the second bonding surface including providing a bonding surface at a temperature of about 125°C to about Made of a third material that resists oxidation at temperatures of 250°C. This third material is interdiffusion into the second material sufficient to bond the two materials and the third material together; Achieved at a temperature of about 125°C to about 250'C. Approximately 12 at a temperature of 5°C to about 250°C, preferably about 200°C Press for sufficient time to interdiffuse the bonded surfaces. The second material and the third material are , are preferably, but not necessarily, made of the same material. When pressing The time period is preferably at most about 1 hour.

Many different systems have been identified as meeting the requirements of diffusion bonding. most preferred A new combination is nickel as the first material and gold as the second and third materials. It is. In another example of a combination that may be used, nickel is the first material and tin is the first material. can be the second and third materials; germanium can be the first material and tin can be the second and third materials; can be the second and third materials; beryllium can be the first material and tin can be the second and third materials; gold can be the second and third materials; further, gold can be the first material and platinum can be the second material; 2 and 3 materials. These examples are illustrative and not limiting. It's not a typical thing.

In a preferred embodiment, more specifically, a method for joining two members to each other is provided. The method involves providing a gold-coated nickel bonding surface on the first member to be bonded; providing a full mating surface on the second member to be mated, and connecting the two mating surfaces together by approximately When the temperature of 125°C to about 250°C is sufficient for interdiffusion of the 5 bonding surfaces. Includes each process of inter-pressing. A preferred bonding temperature is about 200°C.

The temperature of the bond should be low (approximately 125°C).

At lower temperatures, gold or other second material in nickel or other first material This is because the solid solubility of the material is almost zero.

Interdiffusion cannot occur without solubility; experiments have shown that there is sufficient interdiffusion and diffusion. The bonding effect is achieved at temperatures below 250 °C, therefore diffusion bonding at higher temperatures It has been proven that there is no need to do so. In addition, higher temperatures allow the process after completion of the process, resulting in increased heat and residual stresses in the joint and the parts being joined, Therefore, this should be avoided.This invention should be avoided in its current preferred application. When used for electronic device bonding, the device is subjected to temperatures exceeding 250°C. and increased interdiffusion leading to degradation of microelectronic devices. Therefore Therefore, the diffusion bonding range of the present invention is an intermediate temperature of about 125'C to about 250°C. degree range. However, if any of the materials melt at temperatures below 250°C If so, the maximum temperature during diffusion bonding should not exceed its melting temperature.

In a most preferred embodiment of the invention, the method for joining two members to each other comprises: , providing a nickel layer on the first member to be joined; the nickel layer of the first member; The gold layer ensures that the amount of gold present is approximately 0.5% or less of the amount of nickel present. It includes a process of coating to a very thick layer. Provide a nickel layer on the second component to be joined The amount of gold present is of the amount of 0. By coating with a thickness of 5% or less, the second Treat the parts in the same way. so that the gold layers of the first member and the second member are in contact with each other. put. the first member and the second member at a temperature of about 125°C to about 250°C; , pressing the first member and the second member for a sufficient period of time to interdiffuse the first member and the second member.

A preferred embodiment of the invention protects the nickel or other first material from oxidation and provides about 1 nickel or other first material within a temperature range of 25°C to about 250'C. Possible due to the ability of a thin gold layer of gold or other second material to diffuse However, it is completely solid-state diffusion bonding or welding.

Nickel will pressure bond to nickel at such low temperatures and mild pressures. Nickel normally forms nickel oxide on its surface, which interacts with each other. It acts as a diffusion barrier to diffusion and also inhibits nickel at such temperatures. Although the self-diffusion rate is low. Deposition of a thin layer of gold on the surface of nickel Sigon) protects nickel against oxidation and also improves the properties of the nickel-gold phase relationship. yields increased interdiffusion rates.

In a preferred embodiment, at least one of the surfaces to be joined is coated on nickel. nickel is a constituent material of the underlying structure. It can be in the form of a nickel layer deposited on the underlying structure. Others to join one surface has a nickel-gold structure on the opposite surface to interdiffuse with the nickel-gold structure on the facing surface. Must have money. It is also in the form of a thin gold layer on nickel. obtain.

Bonds formed by this method can be formed without the use of etch or flux. This is accomplished under mild temperatures and applied bonding pressures. The method of the invention applies to Can be used if the structure allows these bonding conditions. The final bond is tension and Very strong against creep, superior to that of solder joints formed with low temperature solder Other features and advantages of the present invention which result in improved mechanical properties further illustrate the principles of the invention. As will be apparent from the more detailed description below when considered in conjunction with the accompanying drawings that illustrate: It will be.

Brief description of the drawing FIG. 1 is a flowchart of a method for implementing a preferred embodiment of the invention.

FIG. 2 is a side view showing a preferred joining form just before starting joining, and FIG. 3 is a front view schematically showing the joint portion with the composition indicated.

III 17th day FIG. 1 shows steps in a preferred method of the invention, and FIGS. 2-3 show a preferred embodiment. The structure of the members to be joined is shown both before and after joining. Figure 1 and Referring to FIG.

First, a nickel layer 40 is applied to a first member 42 (20), as used herein. Nickel J is a nickel alloy containing pure nickel and other alloying elements. The alloy is acceptable as long as no brittle phases are formed during interdiffusion, including both. example For example, when lead and gold interdiffuse, they form a brittle phase. should rarely or never be present.

The first member 42 may itself be made of nickel, in which case its The upper part of the member made of nickel is considered layer 40. The nickel layer 40 is a gold layer. 44 (reference numeral 22). Layer 40 may be pure gold or nickel. It may also be a gold alloy that does not form an embrittlement phase during interdiffusion with layer 40.

The nickel and gold layers can be of various thicknesses. However, the gold layer 44 The total amount of gold in the nickel layer 40 is preferably about 0° of the total amount of nickel in the nickel layer 40. Do not exceed 5%.

If the amount of gold exceeds this value, the interdiffused nickel-gold layer obtained in subsequent processing will The net composition is now in the solid solution region of the phase diagram. It will disappear. In fact, the total composition is the solubility gap in the phase diagram. gap) area. Although this relationship is desirable, it is not an absolute requirement. . Partial interdiffusion or interdiffusion into compositions within the solubility gap is particularly important when applied during use. to ensure that there is a sufficiently large area over which any force applied is distributed. is acceptable when achieved over a relatively large bonding surface area.

In a preferred embodiment, the nickel layer 40 is pure nickel and the first member 42 is It was applied by electroplating, which was used as a plating base material. The plated nickel layer 40 is It was approximately 0.004 inch thick. Vacuum deposition of the plated first member 42 The surface of the nickel FJ40 is removed from contaminants and acids by ion cleaning. Cleaned by removing nickel chloride. The gold layer 44 is pure gold and is made of nickel. Following the deposition of the metal layer 40, the shape is formed by in-situ electron beam deposition. accomplished.

Gold layer 44 is approximately 4000 angstroms (400 nanometers) thick. Ta. so that the nickel Fi 40 cannot be recontaminated or reoxidized prior to the deposition of the gold layer 44. Vacuum was not broken between ion cleaning and full deposition.

Using techniques similar to those just described for the first member 42, the second member 46 is Nickel layer 48 (see numeral 24 in FIG. 1) and gold layer 50 (see numeral 26 in FIG. 1) ) has been established. However, it is not necessary to perform this technique. Second member 4 If there is a gold layer 50 on 6 or the entire second member is gold, then on second member 46 The bonding method works well even if the nickel layer is not provided. Ru. In microelectronics, contacts are made of gold or The method of the present invention can be used for such structures. It is.

After depositing each layer on the first and second members by the above method.

The first member 42 and the second member 46 are brought into contact so that the gold layers 44 and 50 face each other! < (code 28). FIG. 2 illustrates this dosage just before bringing layers 44 and 50 into contact. ing. These members 42 and 46 may be brought into contact in a vacuum, or these members may be brought into contact with each other in a vacuum. There is no need to immediately remove the gold layers 44 and 50 from the acid layer. This is because they do not become oxidized or form other types of diffusion barriers.

However, the facing surfaces of layers 44 and 50 become contaminated with contaminants such as dirt and grease. It is necessary to prevent it from being contaminated.

The first member 42 and the second member 46 are heated and pressed at an elevated temperature (not shown). No. 30). This temperature should be at least about 125°C. gold and d This is because nickels do not significantly interdiffuse at temperatures below that temperature. Therefore , the nickel/gold coated parts were kept at ambient temperature before the interdiffusion process. No substantial interdiffusion occurs even when stored at a low temperature (NC temperature). Ma Additionally, the temperature should not exceed about 250°C. Heat when using higher temperature and residual stresses are experienced, sufficient effectiveness is achieved at lower temperatures, and bonding is attempted. This is because there is a possibility that damage may be caused to the members being used.

Each member achieves reasonably complete interfacial contact at the surfaces of layers 44 and 50 and has a strong bond. Press with sufficient force to promote Applying force to a small area for bonding purposes At the joining line, geometric techniques such as the bump technique concentrate the It is possible to expand the applied force. Therefore, the effective applied force is Depends on the geometry of the area. This bonding phenomenon is mainly due to the application of sufficiently high temperatures. pressure plays no direct role other than promoting interfacial contact. stomach. Therefore, applied pressure is not the primary variable to consider in diffusion bonding operations. do not have.

The time required to join members together depends on the joining temperature. 200°C At the preferred bonding temperature, the bond is applied at an applied pressure of about 15,000 bonds per 1,000 square inches. Achieved within 60 minutes at full power. Other studies have shown that on the order of about 5 to 10 minutes It has been shown that shorter times such as 1 hour or more Excessively long times should not be used. Diffuse damage to parts to be joined This is because it can occur.

Figure 3 shows the composition profile near the junction region after some degree of interdiffusion. are doing. During interdiffusion, layers whose boundaries are initially well defined 40.44 ．． 48 and 50, gold from layer 40 interdiffuses with gold from layer 50; The gold from layer 44 interdiffuses with the nickel from layer 40, and the gold from layer 44 interdiffuses with the nickel from layer 40. Figure 3 shows that each layer becomes less clearly defined as it interdiffuses with Kel. The dashed lines indicate where the layers were physically located for the first time and indicate that those layers are no longer of their original composition. It shows that it is not a thing. Nickel layers 40 and 48 are primarily made of nickel. and gold, and the gold layers 44 and 50 have a substantial nickel content.

Finally, the gold and nickel were previously layered in layers 40, 44, 50 and 48. The bonding operation is completed by mutually diffusing the particles more uniformly across the pores.

Typically, the nickel layers 40 and 48 are made of nickel in the respective members 42 and 46. There is a small amount of interdiffusion into the contact between members 42 and 46 due to the interdiffusion layer. It will further help you get dressed.

In the practice of the present invention, first member 42 is made of nickel approximately 00,004 inches thick. layer 40 and a gold layer 44 approximately 4000 angstroms thick.

The second member 46 was entirely gold. The bond is approximately 15,000 volts per square inch. This was achieved in 60 minutes at approximately 200°C with an applied pressure of 100°C.

After joining, when I tried to remove member @2 from the joint, it turned out that it was not at the joint. Destruction occurred in the nickel. In other measurements, the nickel/gold alloy is Has a tensile strength in excess of 8,0OOp s i (bond per square inch) I understand. The nickel/gold alloy has an expected pressure of over 9000 psi. Leap strength was shown. Typical lead-tin solder has a tensile strength of about 5500 ps It had a creep strength of 300 psi. The joining of the present invention is probably Due to the higher melting point of its components, it is stronger than traditional solder joints.

Although specific embodiments of the present invention have been described in detail for the purpose of illustration, the spirit of the present invention and Various modifications are possible without departing from the scope and scope of the invention. Therefore, the present invention There is no limitation except as in the appended claims.

Size 0 Dimensions Procedural amendment November 2, 1994

Claims (17)

[Claims] 1. providing a first bonding surface on a first member to be bonded, the step of providing a first bonding surface on a first member to be bonded; The bonding surface of a first region of a first material; and a first material formed on a first region of the first material and having a composition different from that of the first material; a first layer of a second material, the second material being deposited on the first material at a temperature of about 125°C; forming an oxidation-resistant adhesive coating at a temperature of about 250°C; The material has negligible solid solubility in the first material at temperatures below about 125°C. and increasing finite solid solubility in the first material at temperatures above about 125°C. and the second material has a sufficient amount of the first material to bond the first material and the second material. Interdiffusion into the material is achieved at a temperature of about 125°C to about 250°C. , providing a second abutment surface on a second member to be joined, the step of: providing a second abutment surface on a second member to be joined; The bonding surface is made of a third material that resists oxidation at temperatures of about 125°C to about 250°C. and the third material has enough of the second material to bond the second material and the third material. Interdiffusion into the material is achieved at a temperature of about 125°C to about 250°C. , The first and second bonding surfaces are heated at a temperature of about 125°C to about 250°C. A process in which the bonding surfaces are pressed for a sufficient period of time to allow mutual diffusion. A method for joining two parts to produce a single item, including: 2. The method of claim 1, wherein the second material and the third material are the same type of material. 3. Claims wherein the first region is a layer of a first material deposited on the members to be joined. The method described in Section 1. 4. Claim in which the third material is present as a layer on the surface of the second member to be joined. The method described in 1. 5. 2. The method of claim 1, wherein the bonding time in the pressing step is about 1 hour or less. 6. An article obtained by the method according to claim 1. 7. providing a gold-coated nickel bonding surface on a first member to be bonded; providing a gold bonding surface on a second member to be bonded, and heating the two bonding surfaces to about 125°C; or about 250°C for a sufficient time to allow interdiffusion of both bonded surfaces. A method for joining two parts to produce a single item, including each step. 8. 8. The bonding surface on the second member is gold coated nickel. the method of. 9. 8. The method of claim 7, wherein the temperature during the pressing step is about 200<0>C. 10. An article obtained by the method according to claim 7. 11. providing a nickel layer on the first member to be joined; The gold layer is such that the amount of gold present is about 0.5% or less of the amount of nickel present. Coat it to the desired thickness, providing a nickel layer on a second member to be joined, the nickel layer of the second member comprising: The gold layer ensures that the amount of gold present is approximately 0.5% or less of the amount of nickel present. Coat it to a thick layer, Place the gold layers of the first member and the second member in contact with each other, The first member and the second member are heated at a temperature of about 125°C to about 250°C. and the second member for a sufficient time to interdiffuse. A method for joining two parts to produce a single item, including each step. 12. 12. The method of claim 11, wherein the first member is made of nickel. 13. providing a nickel layer on the first member includes forming a nickel layer on the surface of the first member; 12. The method of claim 11, including the step of depositing a layer of nickel. 14. 12. The method of claim 11, wherein the second member is made of nickel. 15. providing a nickel layer on the second member includes forming a nickel layer on the surface of the second member; 12. The method of claim 11, including the step of depositing a layer of nickel. 16. 12. The method of claim 11, wherein the temperature during the pressing step is about 200<0>C. 17. An article obtained by the method according to claim 11.