JP3206342B2 - Manufacturing method of ceramic IC package - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic IC package, and more particularly, to a PGA (Pin Gr).
The present invention relates to a method of manufacturing a ceramic IC package having pins of the (id Array) type or the like.

[0002]

2. Description of the Related Art In a process of manufacturing a ceramic IC package having pins for connection to a motherboard, such as PGA, a metal wiring made of W or the like formed on a surface of a ceramic substrate manufactured through a normal manufacturing process. After performing electroplating or electroless plating on the layer (metal pad) to form a plating film, brazing the metal pad with a pin and performing Au plating by the same method to manufacture a ceramic IC package. Is completed. After that, an LSI or the like is installed in the cavity of the ceramic IC package, and connection to a metal wiring layer is performed by wire bonding or the like, and then a lid (cover) or the like is provided to enclose the LSI, thereby forming a semiconductor device. Will be completed.

In the first step, there is a problem in how to set conditions in a so-called sintering step of brazing a pin on a metal pad formed on the surface of a ceramic substrate. In this sintering process, Kovar pins are usually used as pins, but it is necessary that the adhesion between the portion including the brazed pins and the underlying ceramic substrate be sufficiently good. One of the requirements for product reliability is that the product is cut, that is, the pin is cut. In addition, it is necessary that the metal wiring layer for wire bonding formed inside the cavity of the ceramic substrate is not deteriorated in the sintering step, and that the wire bonding be performed well after being covered with the Au plating film.

In order to satisfy the above conditions, it is necessary to form a plating film having good adhesion on a metal wiring layer serving as a base.

Conventionally, as a method of forming a plating film on a metal wiring layer, for example, Ni--Co by electrolytic plating is used.
Method of forming alloy plating film, N by electroless plating
A method of forming an i-P plating film and the like can be given. According to the method, a plating film having excellent adhesion to the underlying metal pad and adhesion to the upper layer such as Au plating is formed.

After forming the plating film by the above method,
A sintering step is performed. At this time, a reducing atmosphere consisting of 25% by volume of hydrogen and 75% by volume of nitrogen is usually employed to prevent oxidation of the metal wiring layer. The high content of nitrogen is to reduce the risk of hydrogen explosion and the like.

In the method described above, the manufactured IC
Although there is no major problem with the characteristics of the package, an Au plating film having excellent adhesion to the underlayer has to be used.
Since a considerable thickness of about 2 to 3 μm is required as a plating thickness, there is a problem that manufacturing cost is increased.

[0008]

On the other hand, when a Ni-B plating film is formed on a metal pad by electroless plating, there is no problem with the adhesion to the base, and the Ni-B and the solder have a good wettability. This method has the advantage that a plating film having sufficient performance can be formed even if the Au plating film formed thereon is thinned, and a method of forming a Ni-B plating film on a metal wiring has been studied. I have.

[0009] However, after forming a Ni-B plating film on the metal wiring, hydrogen conventionally used up to 25% by volume of hydrogen is used.
If the sintering step is performed in a reducing gas atmosphere containing 75% by volume of nitrogen and nitrogen, the surface of the plating film is discolored to black or gray brown. The discolored Ni-
A phenomenon in which a sintering aid such as CaO or MgO contained in the ceramic of the substrate rises on the surface of the B plating film also occurs.

For this reason, poor adhesion and partial discoloration of the Au plating film (a phenomenon in which the discoloration of the underlying electroless Ni-B plating film floats on the Au plating film as it is) often occurs, and the product yield is reduced. There was a problem of inviting.

[0011] In order to solve such a problem, a Ni-P plating film is usually formed by electroless plating on the Ni-B plating film to secure the adhesion between the Au plating film and the base. However, since the number of steps is naturally increased, the manufacturing cost is increased, which is not a preferable method.

The present invention has been made in view of such a problem, and when a method of forming a Ni-B film by performing an electroless plating process on a ceramic substrate having a metal wiring layer of W or the like is adopted, In the sintering step, discoloration of the Ni-B plating film and floating of the sintering aid contained in the ceramic substrate on the Ni-B plating film are suppressed, and the surroundings of the Au plating film formed in the next step ( It is an object of the present invention to provide a method of manufacturing a ceramic IC package that improves the adhesion between the Ni-B plating film and the Au plating film.

[0013]

In order to achieve the above object, a method of manufacturing a ceramic IC package according to the present invention is to provide an electroless Ni-B plating process on metal wiring on the surface of a ceramic substrate having a conductor circuit therein. And then brazing the pins on the plating film in a reducing gas atmosphere containing no nitrogen or in an inert gas atmosphere.

[0014]

First, the cause of discoloration after the sintering step of the Ni-B plating film and the method of the present invention for preventing the discoloration will be described. In a Ni-B plating film formed by electroless plating using a plating bath containing dimethylaminoborane (hereinafter, referred to as DMAB) as a reducing agent, B (boron) in addition to Ni is 0.8 wt%. %. This is because a plating film is formed by a chemical reaction represented by the following chemical formulas 1 to 4, and Ni ₂ is contained in the plating film.
This is because B also precipitates.

[0015]

Embedded image 4Ni ²⁺ + BH ₄ ⁻ + 8OH ⁻ → 4Ni + BO ₂ ⁻
+ 6H ₂ O

[0016]

Embedded image 4Ni ²⁺ + 2BH ₄ ⁻ + 6OH ⁻ → 2Ni ₂ B +
6H ₂ O + H ₂

[0017]

Embedded image 3Ni ²⁺ + (CH ₃ ) ₂ NHBH ₃ + 3H ₂ O
→ 3Ni + (CH ₃ ) ₂ H ₂ N ⁺ + H ₃ BO ₃ + 5H ⁺

[0018]

Embedded image 4Ni ²⁺ +2 (CH ₃ ) ₂ NHBH ₃ + 3H ₂
O → Ni ₂ B + 2Ni + 2 (CH ₃ ) ₂ H ₂ N ⁺ + H ₃
BO ₃ + 6H ⁺ + ／ H ₂ As described above, when the ceramic substrate on which the Ni—B plating film containing Ni ₂ B is formed is heated in a gas atmosphere containing nitrogen in the sintering process, The reaction shown in (1) proceeds to produce boron nitride (BN).

[0019]

2B + N ₂ → 2BN As a result of calculating the thermodynamic free energy in the above formula, the free energy is negative and is sufficiently biased toward the generation system, so that the reaction proceeds sufficiently in the sintering step. I know I can.

FIGS. 1A and 1B are graphs showing the results of analysis of the surface of the Ni—B plating film after the sintering process by electron spectroscopy (ESCA). The shaft has strength. (A) is N
A region corresponding to _1S, shows a region corresponding to (b) is B _1S, Sample A, B is obtained by arbitrarily extracting discolored samples, Sample C was carried out the method of the present invention A sample is shown.

From the spectra shown in FIGS. 1A and 1B, it is shown that BN was formed in Samples A and B, which is the main cause of discoloration of the Ni—B plating film after the sintering process. Is determined to be due to the formation of BN. On the other hand, in the present invention, since a reducing gas or an inert gas containing no nitrogen is used in order to suppress the formation of BN in the Ni-B plating film, the sample C shows generation of BN. There is no strong spectrum.

Next, the reason why the sintering aid floats on the Ni-B plating film after the sintering step will be described.

A small amount of a heavy metal element such as Bi, Pb, As, S (sulfur) or the like is mixed as a liquid stabilizer in a commercially available electroless plating solution containing DMAB. These trace metal elements and the like are slightly (about several ppm) inevitably incorporated into the coating. Also, when these trace heavy metal elements and the like are not contained in the plating solution, the formed plating film becomes more pure without containing these heavy metal elements and the like, but when such heavy metal elements and the like are removed from the plating solution, In addition, since the self-decomposition reaction of the plating solution itself cannot be suppressed, a good plating film cannot be formed.

FIG. 2 is a graph showing the result of analyzing the surface of the Ni-B plating film after the sintering step by electron spectroscopy (ESCA). From the spectra shown in FIG. 2, Pb and sintering aid contained in the plating solution were detected in the plating films of Samples A and B. This is because Pb incorporated into the plating film plays a role as a diffusion promoter, and once diffuses into the ceramics in the sintering process, combines with the sintering aid, and then diffuses again into the plating film. It is estimated that there is not.

Sample C obtained by the method of the present invention includes:
No sintering aid has been detected.

Although this mechanism is not clearly understood, the sintering step in the method of the present invention, that is, in a reducing gas atmosphere or an inert gas atmosphere, does not cause the sintering aid to float. In a conventional sintering process in an atmosphere containing nitrogen, it is considered that nitrogen plays some role to lift the sintering aid.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a ceramic IC package according to the present invention will be described below.

FIG. 3 shows PGA before electroless plating.
FIG. 10 is a plan view showing a ceramic substrate of the type 10;
Is a ceramic substrate made of alumina, 11 is a metal pad portion, 12 is a lid sealing portion, and 13 is a wiring portion for wire bonding.

First, the ceramic substrate 10 on which the metal wiring such as the metal pad portion 11 shown in FIG. 3 is formed is subjected to Ni supply source NiSO ₄ , a reducing agent DMAB, a complexing agent such as an organic acid salt, and other components. Electroless plating is performed by dipping in a plating bath containing an accelerator and a stabilizer.
A Ni-B plating film (containing 0.8 wt% of B) having a thickness of μm was formed. The film thickness of 5 μm is a film thickness conventionally used in PGA of electroless plating specifications.

Next, a sintering process was performed, and Kovar pins were brazed to the metal pad portions 11 of the ceramic substrate 10. The brazing temperature varies depending on the composition of the Kovar pin and the brazing material. When a low-temperature eutectic Kovar pin is used, Ag (75 wt%), Cu
(25 wt%) alloy is brazed at 750 ° C. for 10 minutes. When a high temperature eutectic Kovar pin is used, an alloy of Ag (85 wt%) and Cu (15 wt%) is used at 850 ° C. Perform brazing for 10 minutes.

Then, under the above two conditions,
Further, the sintering process was performed while changing the atmosphere to 100% by volume of hydrogen gas and 100% by volume of argon gas, and the adhesion between the ceramic substrate 10 and the brazed portions of the pins was evaluated. As a method for evaluating the adhesion between the ceramic substrate and the brazed pin, the brazed pin is pulled vertically at a speed of 10 mm per minute, when the pin breaks or peels off from the substrate. The strength was shown as the adhesion strength of the pinned portion. The results are shown in Table 1 below.

As a comparative example, the following Table 1 also shows the results of evaluation of the adhesion of the underlayer to the pinned portions when the sintering process was performed in a gas atmosphere of 75% by volume of nitrogen and 25% by volume of hydrogen. .

[0033]

[Table 1]

As is clear from the results shown in Table 1, in the case of the embodiment, a large adhesion strength is obtained, and the portion where the pins are brazed has excellent adhesion with the ceramic substrate as the base. You can see that it is. On the other hand, in the case of the comparative example, the wettability with the silver solder was poor, and peeling occurred in the pad, so that accurate strength could not be measured.

Next, after the sintering step, an Au plating step was performed to form a 0.1 μm thick Au plating film, and the adhesion between the Au plating film and the base was evaluated. In this Au plating process, a plating film was formed by performing plating using both electrolytic Au plating and electroless Au plating. Then, an Au ribbon is bonded to the formed Au plating film,
The adhesion strength was measured.

The specific measurement of the adhesion strength is 100 μm in width.
m, Au having a thickness of 20 μm and a purity of 99.99 wt%
The ribbon was pressed at a pressure of 450 gf and a bonding time of 1.5 seconds to form Au.
The Au ribbon joined to the plating film and joined in a loop was hooked using an appropriate jig, pulled vertically at a speed of 5 mm per minute, and measured for the strength at break. Generally, in the Au wire bonding reliability test, in the above test, it is a condition that the Au wire itself breaks, that is, so-called broken wire,
The strength at this time is about 2 gf or more. Tables 2 and 3 below show the evaluation results of the adhesion strength.

[0037]

[Table 2]

[0038]

[Table 3]

As is evident from the results shown in Tables 2 and 3, in each of the examples, the value was much larger than 2 gf, indicating that the film had sufficiently high adhesion strength. On the other hand, in the case of the comparative example, an accurate strength could not be measured as in the case of the adhesion strength of the pinned portion.

Next, Ni- formed by electroless plating is used.
The thickness of the B plating film was changed from 1 to 10 μm with the values shown in Tables 4 and 5, and the atmosphere was changed to 100% by volume of hydrogen gas and 100% by volume of argon gas in the same manner as described above. 750 ° C, 850
° C, and in each case, the discoloration state of the plating film and the floating state of the sintering aid on the plating film were observed. All of the sintering aid lifting conditions were analyzed using ESCA. The evaluation results are shown in Tables 4 and 5 below. The final evaluation items include, in addition to the state of discoloration of the film and the state of lifting of the sintering aid, whether or not the plated film itself formed by the electroless plating process was good (phenomena such as bleeding). Assessment of whether or not it has occurred) is included.

[0041]

[Table 4]

[0042]

[Table 5]

As is clear from the results shown in Tables 4 and 5, it was found that when the plating film was 3 μm or more, no discoloration of the plating film and no lifting of the sintering aid were observed. When the thickness of the plating film is 8 μm or more, discoloration of the plating film and lifting of the sintering aid are not recognized, but it is not preferable because bleeding occurs in the plating process. Was. However, the discoloration that occurs when the thickness of the plating film is smaller than 3 μm is not caused by the generation of BN, unlike the conventional case. Therefore, it is presumed that the cause of the discoloration was caused by the fact that W used as the underlying metal wiring layer diffused into the Ni plating film.

Of the conditions shown in Tables 4 and 5 above, evaluation was made on the adhesion of the underlayer at the pinned portion and the adhesion between the Au plating film and the underlayer for some of the conditions where the brazing temperature was set at 750 ° C. Was done.

FIG. 4 is a graph showing the results of evaluation of the adhesion of the substrate to the pinned portion, in which the vertical axis represents the adhesion strength of the pinned portion, and the horizontal axis represents the thickness of the Ni-B plating film. . FIG. 5 is a graph showing the results of evaluation of the adhesion between the Au plating film and the underlayer. The vertical axis represents the adhesion strength of the Au plating film, and the horizontal axis represents the thickness of the Ni—B plating film. I have.

As is clear from the results shown in FIGS. 4 and 5, the thickness of the Ni—B plating film is about 2 μm to about 10 μm.
Between m, the adhesion strength of the pinned portion and the adhesion strength of the Au plating film hardly depend on the film thickness, are almost constant, and have sufficient strength.

Table 6 below shows the case where the method of manufacturing the ceramic IC package according to the example was performed based on the various results described above, and the case where the method of manufacturing the conventional ceramic IC package according to the comparative example was performed. 3 shows the discoloration state of the plating film, the floating state of the sintering aid on the plating film, and the defect rate of the product determined from the adhesion strength of the pinned portion and the adhesion strength of the Au plating film. The thickness of the Ni—B plating film formed at this time is 5 μm, and the condition in the sintering step is a temperature of 750 ° C. for 10 minutes.

[0048]

[Table 6]

As is clear from Table 6, in the case of the comparative example, a considerably defective product was manufactured, but in the case of the example, the defect rate was 0%. It has been demonstrated that the IC package manufacturing method is excellent.

[0050]

As described in detail above, in the method for manufacturing a ceramic IC package according to the present invention, the metal wiring on the surface of the ceramic substrate having the conductor circuit therein is formed.
After performing the electroless Ni-B plating treatment, the method includes a step of brazing pins on the plating film in a reducing gas atmosphere containing no nitrogen or in an inert gas atmosphere. Ni- formed by B plating
It is possible to suppress discoloration of the B-plated film and floating of the sintering aid contained in the ceramic substrate on the Ni-B-plated film. And the adhesion between the Au plating film) and the ceramic IC package having excellent performance.

Further, since the Au plating film has good throwing power, the thickness of the Au plating film itself can be reduced, and the manufacturing cost can be reduced.

[Brief description of the drawings]

1 (a) and 1 (b) show Ni—B after a sintering step.
It is the graph which showed the result of having analyzed the surface of the plating film by the electron spectroscopy (ESCA).

FIG. 2 is a graph showing the result of analyzing the surface of a Ni—B plating film after a sintering process by electron spectroscopy (ESCA).

FIG. 3 is a plan view showing a ceramic substrate according to an embodiment before performing an electroless plating process.

FIG. 4 is a graph showing a result of evaluating the adhesion of a base to a pinned portion.

FIG. 5 is a graph showing the result of evaluating the adhesion between an Au plating film and a base.

[Explanation of symbols]

 Reference Signs List 10 ceramic substrate 1 metal pad portion 12 lid sealing portion 13 wiring portion for wire bonding

Continuation of the front page (56) References JP-A-61-104085 (JP, A) JP-A-1-214150 (JP, A) JP-A-3-200359 (JP, A) JP-A-6-264284 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23/50 H01L 23/12 H01L 21/60 C23C 18/00

Claims (1)

(57) [Claims] An electroless Ni-B plating process is performed on a metal wiring on the surface of a ceramic substrate having a conductive circuit therein, and then, in a reducing gas atmosphere containing no nitrogen or in an inert gas atmosphere, Ceramics I, characterized by including a step of brazing a pin on a plating film.
Manufacturing method of C package.