JPH08199344A - Metallic layer for soldering connection - Google Patents

Abstract

PURPOSE: To provide a metallic layer for soldering connection small in solder spending rate, and an electronic circuit device using the same. CONSTITUTION: This metallic layer for soldering connection is formed by sputtering or vapor depositing an alloy comprising 0.5-5atom.% one of Al, Co, Cd, Fe, Ga, Ge, Mg, Mn, Mo, Pd, Pt, Ru, Si, Sb, Sn, V and Zn and the balance Ni, an alloy comprising 0.5-1atom.% one of Ag, As, Be, In, Pb, Pt and Zr and the balance Ni, an alloy comprising 0.5-5atom.% one of Al, Au, Ca, Cr, Ge, Ga, Mn, Pd, Pr, Pt and Zn and the balance Cu or an alloy comprising 0.5-1atom.% one of As, In, Mg, and Si and the balance Cu on a circuit board 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal layer for solder connection, which has a low consumption rate and maintains good connection even after a large number of soldering operations.

[0002]

2. Description of the Related Art In an electronic circuit device such as a large-sized electronic computer, a large number of electronic circuit components such as LSI are mounted on a printed board or a ceramic board to form an electronic circuit. Typical mounting methods for these are as follows.
First, a metal layer for solder connection is formed on a printed board, a ceramic board or the like (hereinafter referred to as a board). On the other hand, metal terminals for electrodes are formed on the electronic circuit component. After that, both are connected using solder.

After mounting electronic circuit components such as LSI on a substrate,
There is a case where a new component is removed from the substrate for changing the logic of the electronic circuit and the like, and a new component is mounted again (this process is hereinafter referred to as repair). For removal, the solder connection part of the electronic circuit component is heated and melted to remove the component. At this time, a part of the metal layer of the substrate is simultaneously removed from the substrate. The reason for this is that the solder connection is made by alloying part of the metal forming the solder alloy and part of the metal layer, and when removing the solder connection by heating and melting, part of this alloy Or because all are removed at the same time. As an example of a commonly used connection system, in the case of Sn / Pb solder and Ni layer, the connection is established mainly by forming Sn—Ni alloy. When removing electronic parts,
Part of this alloy is removed at the same time. When remounting a new component, a new metal layer in the same place is consumed for solder connection.

Although repair is essential for improving the manufacturing yield of electronic circuit devices, repeated repairs may consume the metal layer and eventually cause it to disappear. In this state, the normal connection is not established, so that the reliability of the solder connection portion is significantly reduced. Or solder connection itself becomes impossible. In order to prevent this, in the past, it has been most common to form a metallized thickness, which is expected to be consumed by repairing an allowable number of times, by a plating method or the like.

On the other hand, in recent years, in order to meet the demands for higher density and finer electronic parts, cleaner metal film forming method for electronic parts, and higher reliability of parts connecting parts, sputtering, vapor deposition, ion plating are performed. In many cases, it is required to form a metal layer for solder connection of about 1 μm or less by a physical vapor deposition method such as coating or a chemical vapor deposition method. In this case, increasing the thickness of the metal layer by sputtering or vapor deposition for the purpose of realizing repairs many times means that the residual stress of these films is several hundred to several times that of the film formed by plating.
Since it is as large as several thousand times, it is not suitable because the residual stress of the formed metal film causes a crack in itself. Due to such an obstacle, conventionally, the number of repairs that can be performed is limited to a small number of times, and the reuse rate of an expensive electronic circuit board is low.

Although there are many descriptions about the metal layer for soldering connection, the document "40th ECTC P
roceedings PP460-469 ， Reliability improvements in
There is solder bump processing for flip chips. "

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solder connecting metal thin film with a low consumption rate during soldering, and an electronic circuit device using the same, since repair can be performed many times. It is in.

[0008]

The above object can be achieved by any of the following means.

That is, the first means is to use Ni, which is a conventional solder connecting metal, with Al, Co, Cd, Fe, Ga,
Ge, Mg, Mn, Mo, Pd, Pt, Ru, Si, S
0.5 to 5 atomic% or less of any one of b, Sn, V, and Zn is added, or Ag, As, Be, I is added.
It is to add a metal of any one of n, Pb, Pt, and Zr to 0.5 to 1 atomic% to form a solid solution with Ni.
Here, the lower limit of the concentration of the added metal is 0.5%,
This is because if it is less than 0.5%, a remarkable effect cannot be obtained.
Also, the upper limit is 5%, and if it is larger than this, N is originally
This is because the reliability of the connection obtained by the i metal layer is not guaranteed. Here, the upper limit of the concentration of the latter group is 1% because the solid solubility limit of each metal in Ni at room temperature is 1%.
Because it is%.

The second means is to use Al, Au, Ca, Cr, Ge, Ga and M in addition to Cu which is a conventional solder connecting metal.
0.5 of any one of n, Pd, Pr, Pt, and Zn is added.
~ 5 atom% or As, In, Mg,
It is to add 0.5 to 1 atomic% of any metal of Si to form a solid solution with Cu.

[0011]

The operation of the present invention will be described below with reference to the drawings.

Generally, the stability of the phase of an alloy is described by the Gibbs free energy, and the free energy G ₂ of a _binary solid solution consisting of the elements A and B is expressed by the equation 1.

[Equation 1] G ₂ = G ₁ + ΔG mix (Equation 1) Here, [Equation 2] G ₁ = XaGa + XbGb (Equation 2), where Xa and Xb are the mole fractions of element A and element B in the solid solution, respectively. Rate (Xa + Xb = 1), Ga and Gb are free energies per mole of element A and element B, ΔGmix
Is the change in free energy due to mixing (Figs. 1 and 2
reference). In general, when enthalpy is H, entropy is S, and absolute temperature is T, the free energy G is [Equation 3] G = H-TS (Equation 3), so [Equation 4] G ₁ = H ₁ -TS ₁ (Equation 4) [Equation 5] G ₂ = H ₂ -TS ₂ (5) In addition, [6] ΔHmix = H ₂ -H ₁ (6) [Equation 7] ΔSmix = S ₂ - S ₁ (Equation 7) By substituting Eqs. 5 to 8 into Eq. 2, [Equation 8] ΔGmix = ΔHmix−TΔSmix (Equation 8) ΔHmix is heat generation or heat absorption due to mixing in FIG. 8, ΔSmix
Is the difference in entropy before and after mixing. Here, the volume change due to mixing is ignored. From the definition of entropy, [Equation 9] S = klnω (Equation 9) where k is Boltzmann's constant and ω is randomness [Equation 10] ω = (Na + Nb)! / Na! Nb! (Equation 10) And Na and Nb are the numbers of atoms of element A and element B, respectively. If the Avogadro number is NA, [Equation 11] Na = XaNA (Equation 11) [Equation 12] Nb = XbNA (Equation 12) Equations 9, 10 and Stirling's approximate expression (lnN! ≈Nln−
N), and using [Equation 13] kNA = R (R is a gas constant) (Equation 13), [Equation 14] ΔSmix = −R (XalnXa + XblnXb) (Equation 14) Next, the binding energy of the binary solid solution Consider FIG.
In the schematic diagram of, three types of bonds are possible. Here, the binding energy of AA is represented by εaa, the binding energy of BB is represented by εbb, and the binding energy of AB is represented by εab. The state where the atoms are separated at infinity is 0, and εaa,
The values of εbb and εab are negative. Where AB
When the number of bonds is represented by Pab, [Equation 15] ΔHmix = Pabε (Equation 15) where ε is the AB binding energy and AA and BB
It is a difference in average of binding energies and is represented by [Equation 16] ε = εab− (εaa + εbb) / 2 (Equation 16). Also, if the number of AB bonds is Pab, and the number of bonds per atom is Z, [Equation 17] Pab = NAZXaXb (Equation 17) Therefore, from Equations 16 to 18, [Equation 18] ΔHmix = ΩXaXb (Equation 18) (Equation 18) Here, when [Equation 19] Ω = NAZε (Equation 19) Ω> 0, the change of ΔHmix is as shown in FIG. Ω
When <0, it is convex downward. In any case, Xa
The slope of the graph at = 0 and 1 depends on Ω.

From the equations (8), (14) and (18) above, the change in free energy due to mixing is expressed by [Equation 20] ΔGmix = ΔHmix−TΔSmix = ΩXaXb + RT (XalnXa + XblnXb) (Equation 20) = Positive / negative of ΔHmix), and a change in ΔGmix depending on the magnitude of T are schematically shown. ΔHmix <
In the case of 0, ΔGmix <0 in all temperature ranges,
The mixing reduces the free energy of the system. ΔHmix> 0
In the case of, TΔSmix is larger than ΔHmix and ΔGmix <0 at all compositions at high temperature. On the other hand, at low temperature, TΔSmix becomes smaller than ΔHmix near the center of the composition, and ΔG
mix> 0. Near both ends of the composition, that is, Xa, Xb → 0
Then, from equation (14), the slope of -TΔSmix approaches minus infinity. On the other hand, the slope of ΔHmix is a finite value that depends on Ω as described above. Therefore, the value of ΔGmix is negative in the vicinity of Xa, Xb → 0. These are put together and FIG. 6 is obtained from FIG. 2 and FIG. From the above, ΔGmix due to the addition of a small amount of the second element is negative except at absolute 0 degrees,
It can be seen that mixing a small amount of the second element reduces the free energy of the system.

The formation rate of the intermetallic compound formed by the Ni alloy or Cu alloy and the molten solder is considered to depend on the elution rate of the Ni alloy or Cu alloy into the molten solder. It is generally known that, unlike isothermal growth of phases, the migration velocity Vn of atoms between phases that is controlled by diffusion without depending on nucleation is represented by the following equation.

[Equation 21] Vn = sνexp (−ΔGn / kT) (Equation 21) Here, ΔGn is the activity required for one atom to leave the phase γ and cross the interface to move to another phase η. It is the energy of conversion. Further, ν is the frequency (the number of times that one atom tries to cross the energy barrier per second), and s is the number of atoms that cross the interface. Therefore, the rate of movement of Ni atoms from the solid phase pure Ni into the molten solder, or the solid phase pure C
The speed V ₁ at which Cu atoms move into the molten solder from u, and the speed at which Ni atoms move into molten Sn from the Ni alloy added with a small amount of the second element α, or a small amount of the second element α was added. The velocity V ₂ at which Cu atoms move from the Cu alloy into the molten solder is expressed as follows using this.

[Equation 22] V ₁ = sνexp (−ΔG ₁ / kT) (Equation 22) [Equation 23] V ₂ = sνexp (−ΔG ₂ / kT) (Equation 23) Here, ΔG ₁ is shown in FIG. 7. As described above, the activation energy required for the Ni atoms in the solid phase pure Ni or the Cu atoms in the solid phase pure Cu to move into the liquid phase solder, and ΔG ₂ are
It is the activation energy required for the Ni atoms in the Ni alloy added with a small amount of the second element or the Cu atoms in the Cu alloy added with a small amount of the second element to move into the liquid phase solder. As discussed above, the free energy G (Ni + α) of the Ni alloy added with a small amount of the second element or the free energy G (Cu + α) of the Cu alloy added with a small amount of the second element is pure Ni. Free energy of G (N
i) or smaller than the free energy G (Cu) of pure Cu. Therefore, in FIG. 7, ΔG ₂ > ΔG ₁ , and as a result, V ₂ <V ₁ .

That is, a small amount of the second element is added to Ni or Cu.
The moving speed of the alloy in which the above metal is dissolved into the molten solder is smaller than that of pure Ni or pure Cu, and the consumption speed during soldering is small.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 8 shows an LSI chip having Au-plated electrode terminal portions on a ceramic multilayer wiring board having a solder connecting metal layer consisting of 98 atomic% Ni and 2 atomic% Co. FIG. 3 is a perspective view showing an outline of an electronic circuit device which is an embodiment of the present invention, which is connected by minute solder balls having a composition of Ag, Ag 3 wt%, and the balance Sn.

The electronic circuit device of the present embodiment has a plurality of LSs.
The I chip 7 is arranged on the multilayer wiring board 8 according to a predetermined layout pattern, the heat conduction relay member 11 is placed on the LSI chip, and the multilayer wiring board 8 is placed on the relay member 11.
Place the cap 10 that covers this on the
A cooling plate 9 is laminated on the upper surface of 0. The multilayer wiring board 8 is connected to the wiring board 13 via the connection pins 12 to form an electronic circuit.

Next, a method of manufacturing this electronic circuit device will be described.

First, a method of forming a solder connecting metal layer composed of 98 atomic% of Ni and 2 atomic% of Co on a ceramic multilayer wiring board, which is a feature of the present invention, will be described. First, an apparatus capable of simultaneously sputtering a plurality of targets, for example, a binary simultaneous ion beam sputtering apparatus, is used as a target.
Attach a 9% Co plate in place. Next, the ceramic multilayer substrate is covered with a stainless mask with a predetermined pattern removed, and the ceramic multilayer substrate is set at a predetermined position in the sputtering apparatus. Next, the Ni and Co targets are simultaneously A
A film in which Ni and Co are mixed is laminated to a film thickness of 1 μ on the ceramic multilayer substrate by sputtering with an r ion beam or the like. At this time, the composition ratio after lamination is Ni: Co = 98: 2.
The sputter strength is adjusted so that

Further, the LSI chip 7 having Au plating on the portion to be soldered, the cooling plate 9 and the cap 1
0, heat conduction relay member 11, connection pin 12, wiring board 1
Prepared 3. Also, as the first solder, Ag 3 wt%
-A fine solder ball having a composition of 97 wt% Sn,
Sn 37 wt% -Pb 45 wt% -as the second solder-
A solder alloy having a composition of Bi 18 wt%, a solder alloy having a composition of Pb 98 wt% -Sn 2 wt% as a third solder, and a silver solder having a composition of Ag 72 wt% -Cu 28 wt% were prepared. .

After that, first, a silver solder 17 is interposed between the back surface of the ceramic wiring board 8 and the connection pin 12
Both are connected by performing a process of heating to 00 ° C. and then cooling (hereinafter simply referred to as heat treatment).

Next, between the metal thin film portion for solder connection of the present invention on the surface of the ceramic multilayer wiring substrate 8 and the electrode terminal of the LSI chip 7, a minute solder ball 14 made of the first solder alloy is formed. The two are connected by performing a heat treatment at 240 ° C. with the interposition of.

On the other hand, between the cooling plate 9 and the cap 10,
Both are connected by performing a heat treatment at 340 ° C. with the third solder alloy 16 interposed.

Further, after the heat conduction relay member 11 is arranged on the LSI chip 7 connected to the ceramic multilayer wiring board 8, the periphery of the ceramic multilayer wiring board 8 and the cooling plate 9 and the cap 10 which have been previously connected are arranged. The second solder alloy 15 is interposed between the peripheral portion on the cap 10 side and 200
Both are connected by performing a heat treatment at ℃.

Next, the connection method using the metal thin film for solder connection according to the embodiment of the present invention is a technical subject of the present invention, in which the consumption speed of the metal layer for solder connection is small, and multiple repairs are possible. I will specifically verify whether there is.

In order to carry out a repair experiment, in the manufacturing process, an LSI chip was placed on a ceramic multilayer wiring board with a fine solder ball made of a first solder alloy interposed between them to obtain a temperature of 250 ° C.
By performing the heat treatment of 2 minutes for 2 minutes, a sample in which both are connected is prepared.

For comparison, an experimental sample similar to the one prepared by the conventional method for the solder connecting metal thin film on the ceramic multilayer wiring board is prepared. As a metal layer for conventional solder connection, 1 μm of Ni is sputtered. Similarly, this sample is heat-treated at 250 ° C. for 2 minutes with a small solder ball made of the first solder alloy interposed therebetween to connect the two.

Next, these two samples were embedded in an epoxy resin, cut so that the joint cross section of the solder and the metal layer for solder connection could be observed, and then polished, and the remaining thickness of the metal layer for solder connection was measured by an electron microscope. It was measured using. As a result, the remaining thickness of Ni, which is the conventional metal layer, was 0.3 μ, whereas the remaining thickness of Ni2% Co, which is the metal layer according to the present invention, was 0.6 μ. From this, it was verified that the Ni2% Co alloy, which is one embodiment of the present invention, has a low consumption rate, and therefore, repair can be performed using the metal layer having the remaining thickness.

Although the above is only one example of the present invention, the following experiment was conducted separately in order to confirm the consumption rate of the metal layer when another metal was added to Ni.

Ni with a purity of 99.99% has a purity of 99.9.
A Ni alloy in which 9% of Pd, Ge, Fe, and Co were mixed so as to be 2 atomic% was produced in a vacuum melting furnace.
After this Ni alloy was rolled to a thickness of 50 μm, a region was formed with a resist as shown in FIG. 9 in order to make the solder wet spread region constant when reflowing the solder. Sn-3Ag solder (diameter 2mm,
6 pieces of each composition were prepared by placing a length of 20 mm) together with a sufficient amount of flux for 5 minutes and 60 minutes at 250 ° C. in an electric furnace in an air atmosphere.
After heating and holding for 120 minutes, 180 minutes, 240 minutes, and 300 minutes, air cooling was performed. For comparison, the same experiment was performed only for pure Ni to which the second metal was not added.

The sample after solder heating and melting was embedded in an epoxy resin, cut and polished, and the remaining thickness of the Ni alloy and the thickness of the compound formed at the solder / Ni alloy interface were measured with a metallurgical microscope. Each thickness is 3 per sample
It was based on the average value of the measured values on a metallurgical micrograph (magnification: 1000 times).

FIG. 10 shows Sn3 for various Ni alloys.
The relationship between the average thickness of the compound formed by heat treatment of Ag and the heat treatment time is shown in a graph.

FIG. 11 shows Sn3 for various Ni alloys.
The graph shows the relationship between the remaining thickness of the Ni alloy after heat treatment of Ag and the heat treatment time.

As a result, the Ni alloy added with the second metal has a slower compound formation rate than the pure Ni and the remaining thickness of the Ni alloy is large. It turns out that is small. Therefore, when it is used as a metal layer for solder connection of an electronic circuit device, it is possible to repair a large number of times.

Although an example of a solder-connecting metal layer made of a Ni-based alloy has been described above, the same phenomenon can be achieved by adding a small amount of the second metal forming a solid solution with Ni, which is described in the claims. Occurs, and many repairs are possible.

Further, the same phenomenon occurs even when a small amount of the second metal forming a solid solution with Cu is added as described in the claims, and repair can be performed many times.

[0041]

According to the present invention, it is possible to realize a metal layer having a low consumption rate during heat treatment for soldering, which can be repaired many times. In order to improve the manufacturing yield of electronic circuit devices, especially electronic computers, which will be integrated with higher density in the future, repair of LSIs will be essential.
It can make a big contribution.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a change in free energy due to mixing.

FIG. 2 is an explanatory diagram showing a change in free energy and a composition field relationship before mixing.

FIG. 3 is an explanatory view showing an interatomic bond of a solid solution.

FIG. 4 is an explanatory diagram showing a change in ΔHmix depending on a mixed composition.

FIG. 5 is an explanatory diagram showing the effect of ΔHmix and T on ΔGmix.

FIG. 6 is an explanatory diagram showing a relationship between G1 and G2.

FIG. 7 is an explanatory view showing a change in free energy with the movement of atoms of solid phase Ni into molten Sn.

FIG. 8 is a perspective view showing a configuration of an electronic circuit device according to an embodiment of the present invention.

FIG. 9 is a perspective view showing the shapes and sizes of a Ni alloy plate and a resist.

FIG. 10 is a characteristic diagram showing the relationship between the average thickness of compounds formed of various Ni alloys and the heat treatment time.

FIG. 11 is a characteristic diagram showing the relationship between the average remaining thickness of various Ni alloys and the heat treatment time.

[Explanation of symbols]

 9 ... Cooling plate, 10 ... Cap, 11 ... Heat conduction relay member, 12 ... Connection pin, 13 ... Wiring board, 14 ... Solder ball, 15 ... Solder alloy, 16 ... Solder alloy, 17 ... Solder alloy.

Claims (4)

[Claims] 1. Al, Co, Cd, Fe, Ga, Ge, M
g, Mn, Mo, Pd, Pt, Ru, Si, Sb, S
A metal layer for solder connection, characterized in that an alloy made of 0.1 to 5 atomic% of any of n, V and Zn and the balance of Ni and unavoidable impurities is formed by physical vapor deposition or chemical vapor deposition. . 2. Ag, As, Be, In, Pb, Pt, Z
A metal layer for solder connection, characterized in that an alloy, in which any of r is 0.1 to 1 atomic% and the balance is Ni and unavoidable impurities, is formed by physical vapor deposition or chemical vapor deposition. 3. Al, Au, Ca, Cr, Ge, Ga, M
Any of n, Pd, Pr, Pt, and Zn is 0.1
A metal layer for solder connection, characterized in that an alloy consisting of -5 atomic% and the balance Cu and unavoidable impurities is formed by physical vapor deposition or chemical vapor deposition. 4. An alloy comprising any one of As, In, Mg, and Si of 0.1 to 1 atomic% or less and the balance of Cu and unavoidable impurities is formed by physical vapor deposition or chemical vapor deposition. Characteristic solder connection metal layer.