JP4345075B2 - Copper and copper-based alloy excellent in wire bonding property and die bonding property and manufacturing method thereof - Google Patents

Description

【００３５】
本発明合金１〜５においては、いずれも結晶粒径を１０μｍ以上１５０μｍ以下とし、最終圧延時の圧延ロールの中心線平均粗さ（Ｒａ）を０．１５μｍ以下に制御することで、材料の表面粗さをＲａで０．１５μｍ以下に制御した。また、試験片を５％の硫酸で洗浄することで、酸化皮膜を６ｎｍ以下に制御した。この結果、いずれも均一なはんだ厚さ及びはんだ濡れ性、また良好なワイアーボンディング性が得られていることが分る。
【００３６】
一方、結晶粒径の小さい比較例Ｎｏ．６〜８では、ワイアーボンディング性に優れていても、均一なはんだ厚さが得られていない。特に、比較例８は粗さの比率も１／２超えていた。
また、圧延ロールの中心線平均粗さＲａが大きく、酸洗浄を行っていない比較例Ｎｏ．９〜１０は、材料の中心線中心線平均粗さＲａが大きく、また酸化皮膜厚さも厚かった。この場合、いずれもワイアー破断率が小さく、接合強度及びはんだ付け性とも低下していた。
【００３７】
比較例１１，１２は、圧延ロールの中心線中心線平均粗さＲａが大きい例である。この場合、結晶粒径、酸化皮膜厚が本発明の範囲を満たしているものであっても、ワイアー破断率が低下していた。
【００３８】
比較例１３，１４は、結晶粒径が本発明の範囲を越えている例である。比較例１３は酸化皮膜も厚いため、はんだ付け性も劣り、またワイアー破断率も低下していた。また、粗さの比率が１／２超えていた比較例１４では、はんだの均一性に劣っていた。
比較例１５は、酸化皮膜厚さが厚い例である。この場合、はんだ付け性に劣ることが分る。
【００３９】
比較例１６は、結晶粒径および表面粗さが本発明の範囲を越えている例である。この場合、はんだの均一性、ワイアー破断率の低下が観察された。また、比較例１６は粗さの比率も１／２超えていた。
【００４０】
すなわち、結晶粒径が１０μｍ以上１５０μｍ以下で、表面酸化皮膜が６ｎｍ以下で、中心線平均粗さ（Ｒａ）が０．１０μｍという条件を備えた本発明のみ、はじめて従来のめっき材である従来品１７〜２０並みのワイアーボンディング性、はんだ付け性及びはんだの均一な広がり性が得られることが分る。ここで、従来のＮｏ．１７〜２０はＮｉめっき品であり、コスト面で問題がある。従って、本発明は従来のＮｉめっき品に相当するボンディング性、はんだ付け性及びはんだの均一性による歩留まりの安定性を得たものであり、大幅なコスト削減が可能である。
【００４１】
【発明の効果】
本発明および本発明法は銅及び銅基合金において、結晶粒径、表面酸化皮膜の厚さ及び表面粗さの大きさや形状を共に制御することによって、これまでなし得なかったベア材でのワイアーボンディング性と同時にダイボンディング性を可能としたものであり、信頼性が要求されるリードフレーム材において、めっき工程を省略することが可能となり、大幅なコスト低減を実現できる極めて実用価値の高いものである。
【図面の簡単な説明】
【図１】本発明合金の結晶組織の顕微鏡写真（×７５）である。[0001]
BACKGROUND OF THE INVENTION
The present invention directly solders a chip (bare die bonding) without using a flux when mounting the chip (die bonding) on copper and a copper base alloy for a lead frame material of a semiconductor device, and leads for wire bonding The present invention relates to a copper and a copper-based alloy excellent in wire bonding property and die bonding property that enables direct bonding to a lead frame material (bare wire bonding), and a manufacturing method thereof.
[0002]
[Prior art]
Conventionally, in a semiconductor device, a lead frame material made of copper or a copper alloy is first formed into a predetermined shape by punching or etching, and then the semiconductor element and the lead frame material are wire-bonded with aluminum or gold wire. Plating the die pad part and the outer lead part. Then, the semiconductor element is joined to the plated die pad part by soldering or the like (die bonding), and the lead frame and the semiconductor element are joined by wire (wire bonding) and sealed, and then the outer lead part is soldered to the substrate. It was implemented by attaching.
[0003]
As can be seen, plating is indispensable for leadframe materials for bonding leadframe materials and wires (wire bonding) or leadframe materials and semiconductor elements (die bonding) and leadframe materials and substrates. It was.
[0004]
However, in the case of spot plating on a minute part, very high accuracy is required, and the quality of plating affects die bonding and wire bonding, and in some cases, defective products may occur. This problem can be solved by performing full-surface plating, but there is a drawback that it is too costly in the case of full-surface plating.
[0005]
For this reason, a technique for bonding using a paste at the time of die bonding of a semiconductor element has been developed, and thus a method of omitting plating has been developed. However, the lead frame portion has problems such as durability and electrical conductivity. In addition, expensive noble metal plating such as Au or Ag is still required. Therefore, the total number of processes does not decrease and does not lead to cost reduction. In particular, this problem is a major obstacle in discrete lead frames where the demand for cost reduction is becoming strict, and the demand for plating-less is very strong.
[0006]
Further, a flux is usually used during die bonding and soldering of the lead portion, but cleaning of this residue has also become a problem. That is, the use of chlorofluorocarbons, which have been used as a normal cleaning agent, is prohibited due to the problem of ozone layer destruction, and the regulation of alternative cleaning agents (alternative chlorofluorocarbons and chlorine-based cleaning agents) is becoming stricter. Under these circumstances, semiconductor products have been increasingly mounted with higher density in recent years, and the spacing between components has become narrower. Even a small amount of flux residue can cause short circuits such as migration. ing. There are few effective cleaning methods for removing the flux, and development of an effective cleaning agent is awaited. On the other hand, materials that can be mounted without using cleaning, that is, without using flux (non-flux die bonding and soldering) Development of materials that can be used is required.
[0007]
[Problems to be solved by the invention]
In response to this situation, much research has been conducted on a method of directly bonding a lead frame and a bonding wire without plating, that is, a bare wire bonding. In order to improve the bare wire bonding property, for example, Japanese Examined Patent Publication No. Sho 62-46071 has been studied in the past from the viewpoint of the lead frame material. Here, the surface roughness of the material is set to the maximum surface roughness (Rmax). It is disclosed that the bare bonding property is improved by setting it to 0.5 μm or less, or by further setting the single area of precipitates and inclusions to 3 × 10 ⁻⁶ mm ² or less.
[0008]
However, in order to actually set the maximum surface roughness (Rmax) to 0.5 μm or less, it is necessary to grind the rolling roll extremely smoothly, which requires enormous cost and time. Further, in order to make the single area of precipitates, inclusions, etc. 3 × 10 ⁻⁶ mm ² or less, it is necessary to control severe heat treatment conditions, and it is difficult to deal with as a mass production process.
[0009]
In order to implement bare solderability without flux, for example, Japanese Patent Application Laid-Open No. 11-12714 discloses a technique for reducing the thickness of the oxide film on the surface of the frame by acid cleaning. However, in chip bonding (die bonding) of the die pad part, it is required to spread the solder thinly and uniformly. For this reason, the solder is usually supplied after heating the frame, and further, a trowel, a die, etc. are used. A process for making the solder uniform is performed by mechanical processing. In this case, the surface tension of the solder is large only by controlling the thickness of the oxide film, and a uniform spread of the solder cannot be obtained at the die pad portion.
[0010]
The present invention has been made in view of such problems, and proposes copper and a copper alloy having excellent wire bonding properties and excellent die bonding properties in which solder in a die pad portion spreads uniformly and a method for manufacturing the same. Is.
[0011]
[Means for Solving the Problems]
The present inventor conducted extensive studies on various material factors affecting the solderability during die bonding, and found that the oxide film thickness and surface roughness (size) on the frame surface as well as the crystal grain size of the frame material, Found that it is important to control the shape of the surface roughness. That is, if the crystal grain size is not appropriate, the solder will spread evenly at the die pad portion when soldering without flux, even though the surface roughness of the material is sufficiently small and the oxide film thickness is also sufficiently small. However, it was found that die bonding failure may occur.
[0012]
On the other hand, even if the crystal grain size is appropriate, excellent wire bondability cannot be obtained unless both the oxide film thickness and the surface roughness are satisfied. Further, it was found that even with the same surface roughness, the uniformity of the solder differs depending on the shape of the surface roughness. This makes it possible to control the crystal grain size and the surface roughness as well as the oxide film thickness and surface roughness on the surface of the frame for the first time. Was found to be feasible.
[0013]
That is, the present invention
1. A wire bonding property and a die bonding property characterized by having a crystal grain size of 10 μm or more and 150 μm or less, a center line average roughness (Ra) of 0.15 μm or less, and an oxide film thickness of 6 nm or less. Excellent copper and copper base alloy.
[0014]
2. The total amount of 0.01 to 0.5% by weight, P 0.01 to 0.5%, or at least one selected from the group consisting of Fe, Ni, Sn, Zn, Cr, Co, Si, Mg, Ti, and Zr. 5% content, the balance is made of Cu and inevitable impurities, the crystal grain size is 10 μm or more and 150 μm or less, the center line average roughness (Ra) is 0.15 μm or less, and the oxide film thickness is 6 nm or less A copper and copper-based alloy excellent in wire bonding and die bonding, characterized by being
[0015]
3. The total amount is 0.01 to 5% by weight in terms of P 0.01 to 0.5% or one or more selected from the group consisting of Fe, Ni, Sn, Zn, Cr, Co, Si, Mg, Ti, and Zr. 0.5%, and further, if necessary, one or more selected from the group of Mn, Cd, Al, Pb, Be, Te, In, Ag, B, Y, La, Ce, Au, Ca The total amount is 0.01 to 2.0%, the balance is made of Cu and inevitable impurities, the crystal grain size is 10 μm or more and 150 μm or less, and the center line average roughness (Ra) is 0.15 μm or less, Furthermore, the oxide film thickness is 6 nm or less, copper and copper-based alloy excellent in wire bonding property and die bonding property.
[0016]
4). The copper and copper-based alloy having excellent wire bonding properties and die bonding properties according to the above 1 to 3, wherein the crystal grain size is 10 μm to 150 μm or less by heat treatment in an atmosphere having an oxygen concentration of 5% or less Manufacturing method.
[0017]
5. The wire bonding properties according to the above 1 to 3, wherein the heat treatment temperature for setting the crystal grain size to 10 μm or more and 150 μm or less is 300 ° C. or more and 900 ° C. or less, and the heat treatment time is 0.01 to 72 hours. A method for producing copper and a copper-based alloy having excellent die bonding properties.
It is.
[0018]
[Action]
Hereinafter, the reason for limiting the scope of the present invention will be described in detail.
The reason why the crystal grain size is 10 μm or more and 150 μm or less is that a stable and strong bonding force is required between the solder and the chip during die bonding. In particular, when trying to make the mechanical processing method such as soldering and dies thin and uniform, a capillary phenomenon occurs when the solder enters the grain boundary, and the solder tends to spread uniformly. In this case, when the crystal grain size is less than 10 μm, the effect of spreading of the solder due to the capillary phenomenon is small, and uniform spreading of the solder cannot be expected. Therefore, the crystal grain size is 10 μm or more. Further, a coarse crystal grain size larger than 150 μm is not preferable because it impedes the workability of the lead frame. From the balance with other characteristics, the crystal grain size is preferably 20 μm to 50 μm.
[0019]
Regarding the surface roughness, the center line average roughness (Ra) is set to 0.15 μm or less because it is necessary to stably obtain a strong bonding force in bonding the lead frame and the bonding wire. When Ra: 0.15 μm or more, the more stable and strong bonding force was not obtained as the material in which the lead frame was plated. Further, when the surface roughness is Ra: 0.06 μm or less, the uniformity of the solder is lowered and the roll polishing is expensive, which is not preferable. Therefore, the surface roughness of the material is Ra in the range of 0.06 to 0.15 μm, and more preferably Ra is 0.06 to 0.12 μm or less.
[0020]
Further, in order for the solder to spread uniformly, the shape of the surface roughness is preferably concave downward, and the ratio of the height on the convex side to the height on the concave side from the center line is 1: 2 or more, preferably 1: 5 or more is good.
[0021]
The reason why the thickness of the oxide film is 6 nm or less is that the surface oxide film needs to be sufficiently thin in order to perform soldering with non-flux. That is, when the surface oxide film thickness exceeds 6 nm, the bonding strength and solderability between the lead frame and the wire are lowered. Therefore, the surface oxide film thickness of the material is 6 nm or less, preferably 5 nm or less. Here, as the definition of the oxide film thickness, a value obtained by converting the reduced electric energy of the oxide by the constant current electrolysis method into CuO + Cu ₂ O was used.
[0022]
Next, the selection of the additive element of the copper base alloy according to the present invention and the reason for limiting the content range will be described.
(1) P
P has a deoxidizing effect and improves manufacturability during melting and casting. Moreover, there exists a function which improves heat resistance by content of P and formation of a phosphide. Furthermore, there is an effect of improving the bondability and solderability. However, if the P content is less than 0.01% by weight, these effects are insufficient, and the effect of forming a compound with other additive elements to be dispersed and precipitated cannot be sufficiently brought out. On the other hand, if it exceeds 0.5% by weight, the electrical conductivity and solder weatherability are lowered, and the bonding property and solderability are also lowered. Therefore, the content of P is set to 0.01 to 0.50% by weight.
[0023]
(2) Fe, Ni, Sn, Zn, Cr, Co, Si, Mg, Ti, Zr
Fe, Ni, Sn, Zn, Cr, Co, Si, Mg, Ti, and Zr have a function of making the crystal grain size uniform, and also have an effect of improving strength and elasticity. Fe, Ni and Co also form a compound with P to improve heat resistance. Furthermore, moderate inclusion has an effect of improving the bonding solderability. In order to exert this effect, it is necessary to contain 0.01% by weight or more, but if it exceeds 5.5% by weight, the electrical conductivity is remarkably lowered. Moreover, bonding property and solderability are deteriorated, and further, it is economically disadvantageous. Therefore, the total amount of these contents is in the range of 0.01 to 5.5% by weight.
[0024]
(3) Subcomponents As subcomponents, the total amount of one or more selected from the group of ln, Cd, Al, Pb, Be, Te, In, Ag, B, Y, La, Ce, Au, Ca When the content is 0.01 to 2.0%, the above characteristics are further improved. That is, the addition of these elements improves the strength, heat resistance and press workability without reducing the electrical conductivity of the copper-based alloy according to the present invention. However, if the content is 2.0% or more, the bondability and solderability, or the uniform spread of the solder deteriorates. Therefore, the total amount of these contents is in the range of 0.01 to 2.0% by weight.
[0025]
Next, the reason for limiting the range of heat treatment conditions will be described.
The reason why the oxygen concentration is set to 5% or less is that when the heat treatment is performed in an atmosphere having an oxygen concentration of 5% or more at a temperature of 300 ° C. or higher, the oxide film formed on the surface becomes thicker. This is because it becomes difficult to control the thickness. In order to control a uniform and thin oxide film, an oxygen concentration of 1% or less is desirable.
[0026]
The reason why the annealing temperature is set to 300 to 900 ° C. and the annealing time is set to 0.01 to 72 hours is to obtain the crystal grain size shown above. In this case, at a temperature of 300 ° C. or lower, it takes too much time to obtain a predetermined crystal grain size by heat treatment, which is economically disadvantageous. Moreover, it is difficult to control the crystal grain size uniformly at a temperature of 900 ° C. or higher. Therefore, the heat treatment temperature is set to 300 to 900 ° C. In order to uniformly control the crystal grain size, the heat treatment temperature is desirably 400 ° C. or higher and 750 ° C. or lower.
Next, embodiments of the present invention will be described by way of examples.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Example An alloy having the composition shown in Table 1 was melted using a high-frequency melting furnace, heated to 850 ° C., and then hot-rolled to a thickness of 5.0 mm. Next, the thickness was set to 4.8 mm by surface chamfering, and cold rolling and heat treatment were repeated to obtain a plate material having a thickness of 0.25 mm. Under the present circumstances, predetermined heat processing was implemented suitably in the middle process, and also the roughness of the rolling roll at the time of final rolling was adjusted. The plate material thus obtained was subjected to acid cleaning.
[0028]
Next, the crystal grain size, oxide film thickness, centerline average roughness (Ra), 90 ° W bending workability, bonding property, solderability, and uniformity of solder thickness were investigated for the above materials.
For the measurement of the crystal grain size, an etching method using iron chloride was employed. The surface of the test piece was etched with 5% iron chloride and observed with a 150 × optical microscope to determine the crystal grain size. A micrograph (× 75) of the crystal structure at this time is shown in FIG.
The centerline average roughness (Ra) was measured to a minimum unit of 0.01 μm using a universal surface roughness measuring instrument in accordance with JIS B0601. Further, the average of the height in the convex direction and the average of the height in the concave direction from the center line was calculated to obtain this ratio.
[0029]
Solderability was immersed for 9 ± 1 s in a solder bath (Sn: 63 wt%, Pb: 37 wt%) at 270 ± 5 ° C. by a vertical test method. Flux was not used. Solderability is evaluated by measuring the wetted area, where the wetted area is 99% or more is the best (◎), 95% or more is good (○), and less is not possible (×) It was.
[0030]
Regarding the solder thickness, the test piece was placed on a hot plate preheated to 380 ° C. in a reducing atmosphere of 10% hydrogen and 90% nitrogen, and about 1 g of 95Pb-5Sn thread solder was placed on the test piece and melted in the die. After spreading with (super hard material) and air cooling, the thickness was confirmed by SEM and EPMA. Here, the thickness was measured at five arbitrary points, and the variation within 10% was evaluated as ◯. The case where there was a variation of 10% or more or there was an abnormality such as a void was rated as x.
[0031]
For the measurement of the oxide film thickness, constant current electrolysis was performed under the conditions of electrolytic solution: 0.1 N-KCl, current density of 0.25 mA / cm ² , and the amount of reduced electricity was converted to the oxide film thickness. Here, the oxide film was calculated assuming CuO + Cu ₂ O. Also, in the case of an alloy, an oxide film containing an additive element is formed, but the amount of the additive element is small, and the oxide film is considered to be mainly an oxide mainly composed of copper, and the oxide film is formed as CuO + Cu ₂ O. The thickness was calculated.
[0032]
As a bonding property evaluation method, a pull tester was used to determine and evaluate the bonding strength and the wire breakage rate of the following equation.
Wire breakage rate (%) = (number of wire breaks / total number of tests) × 100
The wire bonding was performed using an ultrasonic bonding method under the bonding conditions shown below.
[0033]
Bonding wire material and wire system: Al wire 25 μmφ,
Atmosphere: Ultrasonic output: 0.2 W
Base temperature: Applied pressure: 0.25N
Time: 30ms,
Number of bonding: 20 pieces / sample 90 ° W The bending workability was performed using a bending jig with R = 0.2, in accordance with CES M0002. After the test, the center of the W-bending part where both ends were constrained was magnified 24 times with a stereomicroscope, and it was confirmed whether or not cracking occurred. The results are shown in Table 1.
[0034]
[Table 1]

[0035]
In the alloys 1 to 5 of the present invention, the surface of the material is controlled by setting the crystal grain size to 10 μm or more and 150 μm or less, and controlling the center line average roughness (Ra) of the rolling roll at the final rolling to 0.15 μm or less. The roughness was controlled to 0.15 μm or less with Ra. Moreover, the oxide film was controlled to 6 nm or less by washing the test piece with 5% sulfuric acid. As a result, it can be seen that uniform solder thickness and solder wettability, and good wire bonding properties are obtained.
[0036]
On the other hand, Comparative Example No. having a small crystal grain size. In 6-8, even if it is excellent in wire bonding property, uniform solder thickness is not obtained. In particular, Comparative Example 8 also had a roughness ratio exceeding 1/2.
Moreover, the comparative example No. which the centerline average roughness Ra of a rolling roll is large, and has not performed acid washing | cleaning. Nos. 9 to 10 had a large centerline average roughness Ra of the material and a thick oxide film. In this case, the wire breakage rate was small, and both the joint strength and the solderability were reduced.
[0037]
Comparative Examples 11 and 12 are examples in which the centerline centerline average roughness Ra of the rolling roll is large. In this case, even when the crystal grain size and the oxide film thickness satisfy the scope of the present invention, the wire breakage rate was reduced.
[0038]
Comparative Examples 13 and 14 are examples in which the crystal grain size exceeds the range of the present invention. Since Comparative Example 13 had a thick oxide film, the solderability was inferior and the wire breakage rate was also reduced. Further, in Comparative Example 14 in which the roughness ratio exceeded 1/2, the solder uniformity was inferior.
Comparative Example 15 is an example in which the oxide film thickness is thick. In this case, it turns out that it is inferior to solderability.
[0039]
Comparative Example 16 is an example in which the crystal grain size and the surface roughness exceed the scope of the present invention. In this case, a decrease in solder uniformity and wire breakage rate was observed. Further, Comparative Example 16 also had a roughness ratio exceeding 1/2.
[0040]
That is, the present invention is the only conventional plating material for the first time with the present invention having the condition that the crystal grain size is 10 μm or more and 150 μm or less, the surface oxide film is 6 nm or less, and the center line average roughness (Ra) is 0.10 μm. It can be seen that wire bondability, solderability, and uniform spreadability of solder of about 17 to 20 can be obtained. Here, the conventional No. 17 to 20 are Ni plated products, which are problematic in terms of cost. Therefore, the present invention obtains the stability of the yield due to the bondability, solderability, and solder uniformity equivalent to the conventional Ni-plated product, and can greatly reduce the cost.
[0041]
【The invention's effect】
The present invention and the method of the present invention are based on the control of the crystal grain size, the thickness of the surface oxide film, and the size and shape of the surface roughness in copper and copper-based alloys. Die bonding is possible at the same time as bonding, and it is possible to omit the plating process for lead frame materials that require high reliability. is there.
[Brief description of the drawings]
FIG. 1 is a micrograph (× 75) of a crystal structure of an alloy of the present invention.

Claims (4)

P0.01～0.5% in weight%, the balance being Cu and unavoidable impurities, the grain size is at 10μm or 150μm or less, the center line average roughness (Ra) is not more 0.15μm or less, the center The ratio of the average height in the convex direction to the average height in the concave direction from the line is 1: 2 or more, and the oxide film thickness is 6 nm or less. Excellent copper and copper base alloy. And P0.01～0.5% in weight%, further Fe, Ni, Sn, at least one selected from among the group of Co containing 0.01 to 5.5% in total, the balance being Cu and unavoidable The crystal grain size is 10 μm or more and 150 μm or less, the center line average roughness (Ra) is 0.15 μm or less, the average of the height in the convex direction and the average of the height in the concave direction from the center line. A copper and copper-based alloy having excellent wire bonding property and die bonding property, wherein the ratio is 1: 2 or more and the oxide film thickness is 6 nm or less. 3. The copper and copper base excellent in wire bonding property and die bonding property according to claim 1 or 2 , wherein the crystal grain size is 10 μm or more and 150 μm or less by heat treatment in an atmosphere having an oxygen concentration of 5% or less. Alloy manufacturing method. The wire bonding property and the wire bonding property according to claim 1 or 2 , wherein the heat treatment temperature for setting the crystal grain size to 10 µm or more and 150 µm or less is 300 ° C or more and 900 ° C or less, and the heat treatment time is 0.01 to 72 hours. A method for producing copper and a copper-based alloy having excellent die bonding properties.

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