CN102420203B - Solder bump/metallization layer connecting structure body in microelectronic package and application of solder bump/metallization layer connecting structure body - Google Patents

Abstract

The invention relates to the micro-interconnection technology in the field of microelectronic packaging, in particular to a solder bump/metallization (transition) layer connection structure in microelectronic packaging with good solderability and its application, which is suitable for general microelectronic connection The invention relates to the technical field of manufacturing a metallization transition layer on a middle substrate and a printed circuit board pad, as well as under a solder bump in a flip chip interconnection. The connection structure is formed by connecting solder bumps and a metallization layer. The metallization layer is an alloy layer co-deposited with iron, nickel, and cobalt elements. The weight percentage range of iron is 59-69%, and the weight percentage range of nickel is 31-41%. %, the rest is cobalt; the solder is tin-silver or tin-silver-copper lead-free solder alloy with relatively high melting point. The invention adopts an electroplating method to plate an iron-nickel-cobalt alloy layer on the copper (or nickel) layer. Compared with the iron-nickel coating, the addition of a small amount of cobalt can allow the ratio of iron and nickel content to maintain a lower expansion coefficient in a wider range and remain constant in a wider temperature range.

Description

Solder bump/metallization layer connection structure and its application in microelectronic packaging

technical field

The invention relates to the micro-interconnection technology in the field of microelectronic packaging, in particular to a solder bump/metallization (transition) layer connection structure in microelectronic packaging with good solderability and its application, which is suitable for general microelectronic connection The invention relates to the technical field of manufacturing a metallization transition layer on a middle substrate and a printed circuit board pad, as well as under a solder bump in a flip chip interconnection.

Background technique

Semiconductor integrated circuit components are called "industrial rice". But in general, what people use is a package with a shell. Electronic packaging has many functions such as mechanical support, electrical connection, external field shielding, stress relaxation, heat dissipation and moisture resistance. Today, the rapid light, thin, short, and miniaturization of electronic equipment promotes the rapid development of the electronic packaging industry. In particular, the continuous improvement of chip performance puts forward higher requirements for electronic packaging density. This is mainly manifested in: the number of pins in the package is increasing; the wiring pitch is getting smaller and smaller; the thickness of the package is getting thinner; the proportion of the package body is getting larger and larger.

Among the four basic technologies of electronic packaging engineering, namely thin-thick film technology, micro-interconnection technology, substrate technology, sealing and packaging technology, micro-interconnection technology plays a role in connecting the past and the future. Regardless of whether the chip is mounted on the carrier or the package is mounted on the substrate, micro-interconnection technology must be used. Flip-chip micro-interconnection (FCB) technology is to arrange I/O terminals in the shape of a grid array on the entire chip surface, and the chip is directly mounted on the wiring board in an upside-down manner, and the grid array I/O terminals are connected to the corresponding electrodes on the wiring board. The pads make electrical connections. In this way, more terminals can be arranged in a limited area, so as to meet the requirement of pin narrow pitch in high-density packaging. The key technology in flip-chip micro-connection is to form bumps in the Al wiring electrode area of the original chip, among which solder bumps are the most common. In order to achieve good adhesion between the bump and Al and the passivation layer, and to prevent the element diffusion between the bump metal and Al, a multi-layer metallization layer, namely UBM (under bump metallization), is generally prepared under the bump. Typical adhesion metals are Ti, Cr, TiN, etc., which must form a strong enough adhesion with the electrodes on the chip. Typical barrier metals include W, Mo, Ni, Cu, etc. As a barrier layer, it can effectively prevent the formation of brittle compounds due to element diffusion. Typical connecting layers are Au, Cu, Pd, etc., which should have good solderability with solder alloys. Similarly, when the solder bump is connected to the metal wiring pad on the substrate, the metallization of the substrate pad is also required, that is, TSM (topside metallization). In a general BGA (ball gridarray) package, the chip package is mounted on a printed circuit board, and a metallization layer connected to the solder balls needs to be prepared on the printed circuit board.

In the microelectronics connection process, eutectic tin-lead solder, 37% of which is lead, was generally used in the past. About 20,000 tons of lead is used as solder every year in the world. If these lead-containing electronic products are discarded and buried, the lead in the alloy will be gradually corroded, dissolved, diffused and enriched by the aqueous solution in the natural environment, which will eventually cause serious damage to the natural environment, soil, natural water body and its animal and plant biological chains. Unrecoverable environmental pollution. As a result, people began to look for substitutes for tin-lead solders. At present, they mainly focus on tin-silver, tin-copper, and tin-silver-copper. The melting points of these solders are 30-40°C higher than traditional tin-lead solders. If these lead-free solders are used as bump materials, higher reflow temperatures are required as they react in a liquid state with the under-bump or pad metal layer. During the reflow process under such high temperature conditions, the reaction rate between the metallization layer and the solder will be accelerated. There are functions.

In addition, during the solid-state diffusion process, the interfacial compound layer grows rapidly, and the thick brittle compound and the resulting Kirkendall holes will seriously affect the reliability of the link. In addition, during the use of the package, due to the thermal mismatch between the device and the circuit board material, the connector will be exposed to a thermal cycle stress field, which will lead to fatigue failure of the connector.

Contents of the invention

In view of the above-mentioned actual situation of the prior art, the purpose of the present invention is to provide a solder bump/metallization (transition) layer connection structure and application thereof in a microelectronic packaging with good solderability, so as to solve the problems existing in the prior art. When the lead-free solder is connected to the metallization layer, it is easy to cause the metallization layer to be consumed quickly, making it lose its proper function, and fatigue failure of the connecting body occurs.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A solder bump/metallization layer connection structure in microelectronic packaging, the connection structure is formed by connecting solder bumps and metallization layers, and the metallization layer is an alloy layer co-deposited by iron, nickel, and cobalt elements. The weight percent range is 59-69%, the nickel weight percent range is 31-41%, and the rest is cobalt; the solder is tin-silver or tin-silver-copper lead-free solder alloy with relatively high melting point.

In the solder bump/metallized layer connection structure in the microelectronic package, in the metallized layer, the preferred range of iron weight percentage is 60-65%, the preferred range of nickel weight percentage is 32-35%, and the preferred range of cobalt weight percentage 3-8%.

In the solder bump/metallization layer connection structure in the microelectronic package, the weight percentage range of silver is 1-4%, the weight percentage range of copper is 0-3%, and the rest is tin.

The application of the solder bump/metallized layer connection structure in the described microelectronic package is electroplating or chemically plating a layer of iron-nickel-cobalt alloy on the surface of the conductive substrate or the surface of the non-conductive substrate covered by the conductive film; Paste stencil printing or positioning with balls, and then reflow to form a structure.

The application of the solder bump/metallized layer connection structure in the described microelectronic packaging, the iron-nickel-cobalt alloy coating is used as a ball grid array (BGA) package, flip chip (flip chip), stacked chip package or micro-electromechanical system (MEMS) micro-device packaging, the metallization layer under the solder bump or the metallization layer of the substrate pad.

In the application of the solder bump/metallization layer connection structure in the microelectronic package, the iron-nickel-cobalt alloy plating layer is used as the outermost layer to form a connection structure with the solder bump.

In the application of the solder bump/metallized layer connection structure in the described microelectronic packaging, the iron-nickel-cobalt alloy coating is additionally deposited on the surface with gold, platinum, palladium, tin or alloy coatings thereof, and then forms a connection structure with the solder bump .

The application of the solder bump/metallized layer connection structure in the described microelectronic packaging, the structure is used as a ball grid array (BGA) package, chip flip chip (flip chip), stacked chip package or micro-electromechanical system (MEMS) ) in the microdevice package, the connection between the microdevice and the substrate or printed circuit board.

In the application of the solder bump/metallized layer connection structure in the described microelectronic packaging, the expansion coefficient of the iron-nickel-cobalt alloy coating is adjusted by the content of iron in the coating, which is suitable for substrates with different requirements; the Sn-Ag-Cu solder is based on Process conditions as well as product type adjust the silver and copper content.

In the application of the solder bump/metallization layer connection structure in the described microelectronic packaging, the iron-nickel-cobalt alloy coating is electrodeposited on common copper or nickel metal layers; or, the iron-nickel-cobalt alloy coating is deposited on other types of transition metals layer electrodeposition.

The present invention has the following advantages:

1. The present invention utilizes the iron-nickel-cobalt coating and tin-silver or tin-silver-copper lead-free solder to form a connection structure, and the tin-silver or tin-silver-copper solder exhibits good wettability and Oxidation resistance, can be used as the outer surface layer, the connection structure can be formed by the direct reaction of the solder with the outer surface layer of the metallization layer.

2. The iron-nickel-cobalt coating (metallized layer) of the present invention has good wettability with tin-silver or tin-silver-copper solder, and the liquid reaction speed with the solder interface is very slow, resulting in extremely thin (submicron thickness) and The flat iron-tin compound layer meets the requirement of high reflow temperature in the lead-free soldering process; the growth rate of the compound is extremely slow within the normal operating temperature range of electrical appliances and during solid-state aging. And the connection interface formed with solder has good reliability performance, which is very suitable for the needs of lead-free connection technology in microelectronic packaging.

3. The iron-nickel-cobalt coating/tin-silver or tin-silver-copper solder connection structure of the present invention has good mechanical reliability. Comparable shear strength for braze structures. The cracks mainly occurred in the solder near the compound layer, indicating that the interface is reliable and stable.

4. The content of iron in the coating of the present invention can be adjusted within a certain range to obtain the thermal expansion coefficient closest to other layers; the solder of silver and copper in the solder can be adjusted according to the process requirements, and the growth rate of the interface compound and the reliability of the connector will not be affected after adjustment .

5. The manufacturing process of the iron-nickel-cobalt coating/tin-silver or tin-silver-copper solder connection structure of the present invention is relatively simple and has strong applicability.

6. The present invention can be implemented on the surface of a conductive substrate such as copper or nickel, or on the surface of a non-conductive substrate covered by a conductive film; it can be used as a connection between a micro device and a substrate or a printed circuit board, and the production of chip bumps craft use.

7. In the present invention, other coatings such as gold, platinum, palladium, tin and their alloys can be deposited on the outer surface of the iron-nickel-cobalt coating to improve oxidation resistance and wettability, and then react with tin-silver-copper solder to form a connecting body.

8. In the process of reflow and solid-state aging, the compound grows slowly at the interface between the metallization layer and the solder in the present invention, which can function as a diffusion barrier.

9. The connection interface between the metallization layer and the solder in the present invention has good mechanical reliability. After aging in high temperature environment, the connection interface maintains a high shear strength. The cracks mainly occurred in the solder near the compound layer, indicating that the interface is reliable and stable.

10. The invention adjusts the content of cobalt to change the percentage of iron and nickel in a wide range, and the metallization layer has a lower coefficient of thermal expansion, which reduces the damage caused by cyclic thermal stress during use and improves the service life of the device and safety and reliability. Therefore, the Fe-Ni-Co coating can achieve a low thermal expansion coefficient in a relatively wide range of composition ratios and keep it constant in a wide temperature range.

11. The weight percentage of iron and nickel in the present invention is close to the composition of Invar alloy (Fe64Ni36). Compared with the metallization layer of Invar alloy (Fe64Ni36) with extremely low coefficient of thermal expansion, the composition ratio of iron and nickel can be allowed to float within a certain range. The metallization layer can still maintain a low coefficient of thermal expansion, so its process is easy to control and has strong applicability.

12. The present invention uses the iron-nickel-cobalt alloy coating as the solder bump connection metallization layer in the microelectronics interconnection technology, which can be widely used in the microelectronics packaging industry, and is especially suitable for high-density micro-interconnections in the form of ball grid arrays and flip-chips. technology.

Description of drawings

Fig. 1 is a schematic diagram of flip chip interconnection technology applicable to the coating of the present invention. Among them, 4 chips; 5 lower iron-nickel-cobalt metallization layers; 6 tin-silver-copper solder bumps; 7 pad iron-nickel-cobalt metallization layers; 8 printed circuit boards.

Fig. 2 is a macroscopic cross-sectional view of the iron-nickel-cobalt coating/tin-silver-copper spherical bump connector.

Figure 3 is the microstructure of the Fe-Ni-Co coating/Sn-Ag-Cu interface.

Figure 4 shows the microstructure of copper/tin-silver-copper interface.

Figure 5 is a reflow soldering process curve.

Fig. 6 is the change curve of the thickness of the Fe-Ni-Co coating/Sn-Ag-Cu interface compound with aging days.

Fig. 7 is the fracture surface morphology of the iron-nickel-cobalt coating/tin-silver-copper connector after fracture.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

Example 1

Electroplate a layer of iron-nickel-cobalt alloy on the surface of a conductive substrate such as copper or nickel, or on the surface of a non-conductive substrate covered by a conductive film. The composition and thickness of the electroplating layer can be adjusted according to actual requirements. As shown in Figure 1, the plating layer realized by the present invention can be used as the pad iron-nickel-cobalt metallization layer 7 on the substrate and on the printed circuit board 8, and the bottom of the tin-silver-copper solder bump 6 in the chip 4 flip-chip connection. Iron nickel cobalt metallization layer 5 is used. As shown in Figure 2, the macroscopic cross-sectional view of the iron-nickel-cobalt coating/tin-silver-copper spherical bump connector.

A thin layer of iron-nickel-cobalt layer is plated on the copper substrate by means of electroplating, and its composition is: 60% of iron, 35% of nickel and 5% of cobalt (percentage by weight). Clean the surface of the plating layer with acetone reagent, use a mask with an aperture of 0.75mm to print solder paste bumps on the surface of the plating layer, and then place tin-silver-copper solder balls on it. The composition percentage of solder paste and solder ball is: tin 95.8%, silver 3.5%, copper 0.7%. The reflow soldering process is carried out in the BGA & CSP rework workstation equipment produced by OK Company in the United States, and the reflow process curve used is shown in Figure 5. The sample after reflow soldering was sealed in epoxy resin, and ground, polished, and corroded along the cross-section, and its structure was observed with a scanning electron microscope. The macroscopic cross-sectional view of the connected structure is shown in Figure 3, and the microstructure of the interface is shown in Figure 4. The number 1 in the figure represents tin-silver-copper solder; 2 represents the iron-nickel-cobalt coating; the portion indicated by the arrow is the formed compound layer 3 with a thickness of about 0.2 μm. In contrast, the copper/SnAg-Cu solder interface produces a very irregular copper-tin compound layer (as shown in Figure 5) with a peak thickness of 10 μm. It can be seen that the reaction speed of the iron-nickel-cobalt coating and the solder is very slow. The thermal expansion coefficient of the coating in this embodiment is about 4-10×10 ^-6 /°C, which matches the thermal expansion coefficient of the ceramic substrate (about 5-7×10 ^-6 /°C).

The iron-nickel-cobalt/tin-silver-copper joints prepared above were subjected to aging at 125° C. for different days, and then the thickness of the joint interface compound was measured. Figure 6 shows the change curves of the thickness of the two interface compounds with aging days. In the figure, SnAgCu/Cu is a copper/tin-silver-copper solder joint, and SnAgCu/Cu(FeNiCo) is an iron-nickel-cobalt/tin-silver-copper solder joint. It can be seen that during the solid-state aging process, the growth rate of the FeNiCo/SnAgCu solder interface compound is much lower than that of the Cu/SnAgCu interface, and the thickness of the FeNiCo/Solder interface compound grows extremely slowly. Figure 7 shows the ductile fracture surface morphology of the bonded structure after the solder balls were scratched. All these indicate that the interface formed by the plating layer and the solder has good mechanical reliability.

It can be seen that the iron-nickel-cobalt plating layer/tin-silver-copper connection structure of the present invention not only has a lower rate of compound formation and growth but also has relatively reliable mechanical properties. In the present invention, the iron content in the plating layer can be adjusted according to different connection materials, so that the connection layer has better thermal matching performance, and the content of silver and copper in the solder can also be adjusted according to process requirements. Therefore, the present invention is very suitable for technical fields such as the connection between micro devices and substrates or printed circuit boards in microelectronic packaging, and the production of bumps in chip flip-chip technology.

Example 2

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 59%, nickel 35%, cobalt 6%;

Solder composition: tin 95.8%, silver 3.5%, copper 0.7%.

Example 3

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 63%, nickel 33%, cobalt 4%;

Solder composition: tin 98.5%, silver 1%, copper 0.5%.

Example 4

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 67%, nickel 31%, cobalt 2%;

Solder composition: tin 95.8%, silver 3.5%, copper 0.7%.

Example 5

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 65%, nickel 32%, cobalt 3%;

Solder composition: tin 98.5%, silver 1%, copper 0.5%.

Example 6

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 61%, nickel 34%, cobalt 5%;

Solder composition: tin 95.8%, silver 3.5%, copper 0.7%.

Example 7

The difference from Example 1 is:

The composition of the iron-nickel layer is: iron 69%, nickel 31%;

Solder composition: tin 98%, silver 2%.

Experimental results show that within the scope of the technical solution of the present invention, the Fe-Ni-Co coating/Sn-Ag-Cu connection structure has lower compound generation and growth rate and better connection reliability, and the Fe-Ni-Co alloy coating has excellent wetting properties. Wet performance and oxidation resistance, lower growth rate of interfacial compounds and better mechanical reliability. The composition in the iron-nickel-cobalt coating of the present invention can be adjusted within a certain range, and its iron weight percentage is 59-69%; for the iron-nickel-cobalt alloy coating, only the composition of iron and nickel is in a very small range close to the composition of Invar alloy Within, the material can obtain zero or negative expansion coefficient. By adding a small amount of cobalt element, the proportion of iron and nickel can be allowed to fluctuate within a certain range, and the alloy coating can still maintain a very low or zero expansion coefficient, so its process applicability is stronger. The composition of silver and copper in the tin-silver-copper solder can also be adjusted, and the weight percentage range of silver is 1-4%, and the weight percentage range of copper is 0-3%. The present invention can be realized on the surface of a conductive substrate, or on the surface of a non-conductive substrate covered by a conductive film. The iron-nickel-cobalt coating/tin-silver-copper connection structure can be used as a connection structure between micro-devices and substrates or printed circuit boards in BGA packaging, and can also be used as a bump manufacturing process in chip flip-chip interconnection.

Therefore, the alloy coating can be used as a solder bump connection metallization layer in microelectronic interconnection technology. The iron-nickel-cobalt alloy coating can also be used as the outermost layer to directly connect with solder bumps; gold, platinum, palladium, tin or their alloy coatings can also be deposited on the surface, and then connected to solder bumps. Iron-nickel-cobalt alloy coatings can be electrodeposited over common copper or nickel metal layers; alternatively, over other types of transition metal layers.

Claims (7)

1. A solder bump/metallized layer connection structure in a microelectronic package, characterized in that: the connection structure is formed by connecting a solder bump with a metallized layer, and the metallized layer is made of iron, nickel, and cobalt elements. The deposited alloy layer, the solder is tin-silver or tin-silver-copper lead-free solder alloy with relatively high melting point; In the metallization layer, by weight percentage, the composition of the iron-nickel layer is: iron 59%, nickel 35%, cobalt 6%; correspondingly, by weight percentage, in the solder composition, tin 95.8%, silver 3.5%, copper 0.7%; Or, in the metallization layer, by weight percentage, the composition of the iron-nickel layer is: iron 63%, nickel 33%, cobalt 4%; correspondingly, by weight percentage, in the solder composition, tin 98.5%, silver 1% , copper 0.5%; Alternatively, in the metallization layer, by weight percentage, the composition of the iron-nickel layer is: iron 67%, nickel 31%, cobalt 2%; correspondingly, by weight percentage, in the solder composition, tin 95.8%, silver 3.5% , copper 0.7%; Or, in the metallization layer, by weight percentage, the composition of the iron-nickel layer is: iron 65%, nickel 32%, cobalt 3%; correspondingly, by weight percentage, in the solder composition, tin 98.5%, silver 1% , copper 0.5%; Alternatively, in the metallization layer, by weight percentage, the composition of the iron-nickel layer is: iron 61%, nickel 34%, cobalt 5%; correspondingly, by weight percentage, in the solder composition, tin 95.8%, silver 3.5% , copper 0.7%; On the surface of a conductive substrate, or on the surface of a non-conductive substrate covered by a conductive film, a layer of iron-nickel-cobalt alloy is electroplated or chemically plated; the solder is positioned by solder paste stencil printing or ball placement, and then reflowed to form a structure. 2. according to the application of the solder bump/metallized layer connection structure in the microelectronic packaging according to claim 1, it is characterized in that: the iron-nickel-cobalt alloy coating is used as a ball grid array package, chip flip chip, stacked chip package or In the micro-device package of MEMS, the metallization layer under the solder bump or the metallization layer of the substrate pad. 3. According to the application of the solder bump/metallization layer connection structure in the microelectronic package according to claim 1, it is characterized in that: the iron-nickel-cobalt alloy coating is used as the outermost layer to form a connection structure with the solder bump. 4. according to the application of solder bump/metallized layer connection structure in the microelectronic package of claim 1, it is characterized in that: iron-nickel-cobalt alloy coating deposits gold, platinum, palladium, tin or its alloy coating in addition on the surface , and then form a connection structure with solder bumps. 5. According to the application of the solder bump/metallization layer connection structure in the microelectronic packaging according to claim 1, it is characterized in that: the structure is used as a ball grid array package, flip chip, stacked chip package or micro-electromechanical In the micro-device package of the system, the connection between the micro-device and the substrate or printed circuit board. 6. According to the application of the solder bump/metallized layer connection structure in the microelectronic packaging according to claim 1, it is characterized in that: the expansion coefficient of the iron-nickel-cobalt alloy coating is regulated by the content of iron in the coating, which is suitable for different requirements The substrate; Sn-Ag-Cu solder adjusts the content of silver and copper according to process conditions and product types. 7. according to the application of solder bump/metallized layer connection structure in the microelectronics package as claimed in claim 1, it is characterized in that: the iron-nickel-cobalt alloy plating layer is electrodeposited on common copper or nickel metal layer; Or, iron Nickel-cobalt alloy coatings are electrodeposited over other types of transition metal layers.