TWI479967B - Solder precoating method - Google Patents

Description

Solder precoating method

The present invention relates to a solder pre-coated substrate in which solder is pre-coated on an electrode portion of a circuit board on which electronic components are to be assembled, an assembly substrate using the same, and a solder pre-coating method.

In recent years, with the miniaturization of electronic equipment and electronic components, the electrodes of the electronic circuit board are also formed in a narrow range, and a plurality of electrodes are formed at extremely narrow intervals, so that the arrangement pitch of the electrode portions (pads) of the electronic circuit board is fine. For example, in the case of a semiconductor package, an electronic circuit having a wiring pattern in which a fine pitch is arranged by an insulating film (solder mask) and a wiring pattern region exposed from the insulating film is regarded as a circuit pattern of an electrode portion is used. In the substrate, a solder layer (pre-coated solder) is formed in advance on the electrode portion of the electronic circuit board, whereby the semiconductor wafer terminal (electronic component) can be bonded to the substrate via the solder layer. Here, when the solder pre-coating is performed on the finely pitched electrode portion of the electronic circuit board, it is generally difficult to accurately perform the printing of the solder paste by a screen printing method or the like as usual, and thus generally adopts After the solder paste is completely coated on the circuit board, the solder is pre-coated on the surface of each electrode portion by heating.

However, in the evolution of the arrangement pitch of the electrode portions becoming more and more fine, in the method of applying the solder paste to the substrate by applying the solder paste to the substrate and applying the solder, the solder is pre-coated on the substrate electrode. At the time of the part, various problems occur due to the influence of the surface tension of the solder, the wettability, and the like. Specifically, the following problems occur: 1) as shown in FIG. 4, in each electrode portion 3a, Between 3b, the position of the largest protrusion of the formed solder 4 will be different; 2) as shown in Fig. 5, in the single electrode portion 3, the protrusion of the solder 4 will form a plurality of problems; 3) as shown in Fig. 6. As shown, the formation of the solder layer on the side of the electrode will be prioritized, resulting in a problem that the amount of solder formed on the electrode portion 3 will be reduced. If such a problem occurs, the height of the solder between the electrode portions will fluctuate, resulting in poor bonding with the electronic components.

One of the means to avoid the above problems 1) to 3) can be considered in the shape of the electrode portion (pad). For example, it has been proposed so far that the coupling conductor pattern (electrode portion) is formed by a wiring pattern that becomes a wiring, and a coupling pad that is continuous with the wiring pattern at a position where the bump is provided to the electronic component; And forming a means for coupling the pad width dimension W1 to be larger than the shape of the wiring pattern width dimension W2, in other words, the electrode portion shape is formed by means having a width of a part of the long side direction, which is larger than the wide part shape at the other portion (refer to the patent) Document 1). Further, there has been proposed a method in which the pad (electrode portion) is formed into a shape having a length L and a width W of (L/W) < 10 (see Patent Document 2).

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2000-77441 (Patent Document 2) Japanese Patent Laid-Open No. Hei 5-226825

However, according to the method described in Patent Document 1, since it is necessary to provide a wide portion in the electrode portion, it is disadvantageous to miniaturization of the arrangement pitch, and further, when it is required to further downsize electronic equipment and electronic parts, prediction is difficult to cope with. . On the other hand, the means described in Patent Document 2 is because of the electrode The portion is formed into a specific shape, and a specific solder material is used, and thus there is a disadvantage that the solder material is limited.

On the other hand, an object of the present invention is to provide a solder-pre-coated substrate which can be stably bonded to electronic components by forming a solder layer having a high degree of variation on a plurality of electrode portions arranged at fine pitches, irrespective of solder material, and using the same. The assembled substrate is formed.

As a result of intensive studies to solve the above problems, the inventors of the present invention have found out the causes of the above problems 1) to 3), and have a large influence on both the shape of the upper surface of the electrode receiving portion and the thickness of the electrode portion. Therefore, it has been found that the shape of the upper surface of the electrode portion which is as fine as possible in the arrangement pitch of the electrode portions is a rectangle, and the ratio (L/W) of the electrode length (L) to the electrode width (W) in the upper shape is set to a specific range. The above problem can be solved by setting the thickness of the electrode portion to be equal to or less than the electrode width, and the present invention has been completed.

That is, the solder pre-coated substrate of the present invention is a solder pre-coated substrate in which a plurality of electrode portions are arranged at fine pitches in an opening portion of an insulating film covering the main surface of the substrate, and a solder pre-coating is applied to the electrode portion. The shape of the portion satisfies the following shapes (i) and (ii): (i) the upper surface of the electrode portion is a rectangle having a ratio (L/W) of the electrode length (L) to the electrode width (W) of 6.0 or less (however, L≧W); (ii) The electrode portion thickness (t) is equal to or less than the electrode width (W).

The assembled substrate of the present invention is characterized in that the electronic component is thermocompression bonded using the solder precoated on the solder precoated substrate of the present invention described above.

The solder precoating method of the present invention uses insulation on the main surface of the cover substrate In the film opening portion, a substrate having a plurality of electrode portions is arranged at a fine pitch, and a solder paste is applied to the electrode portion of the substrate, and then solder is applied to the electrode portion by heating. The shape of the electrode portion is set to satisfy the following shapes (i) and (ii): (i) the upper surface of the electrode portion is a rectangle having a ratio (L/W) of the electrode length (L) to the electrode width (W) of 6.0 or less. (However, L≧W); (ii) The electrode portion thickness (t) is equal to or less than the electrode width (W).

According to the present invention, the solder layer formed on the plurality of electrode portions arranged on the substrate at fine pitches will not occur such that the maximum protrusion position is different between the electrodes or a plurality of protrusions are formed in the single electrode portion. The solder layer on the side surface of the electrode is more likely to cause a problem such as a decrease in the amount of solder formed on the surface of the electrode portion. Since it is a good solder layer which does not have a high degree of variation, an effect of forming a stable bond with the electronic component can be obtained. Further, according to the present invention, the solder material used in the formation of the solder layer is not limited, and the arrangement pitch of the electrode portions can be made finer than conventionally.

In the solder pre-coated substrate of the present invention, as shown in FIG. 1, the plurality of electrode portions 3 are arranged at a fine pitch in the opening 2' of the insulating film 2 covering the main surface of the substrate 1, and solder is applied to the electrode portion 3 having a specific shape. Pre-coating (not shown).

In addition, in Fig. 1, (a) is a schematic plan view of the base substrate, and (b) is a schematic cross-sectional view taken along the line x-x in (a), and (c) is the above (a). In the middle, the cross-sectional view of the y-y line is cut.

The electrode portion 3 of the solder pre-coated substrate of the present invention is formed to satisfy the following shapes (i) and (ii): (i) the ratio of the electrode length (L) to the electrode width (W) is exhibited on the upper surface of the electrode portion 3 (L/W) is a rectangle of 6.0 or less (however, L ≧ W); (ii) The thickness (t) of the electrode portion 3 is equal to or less than the electrode width (W).

In this case, the ratio (L/W) of the electrode length (L) to the electrode width (W) set to the electrode portion 3 of the present invention is 6.0 or less, and the thickness (t) is at the electrode width (W). Hereinafter, a good solder having no height variation can be formed on the surface (upper surface). Preferably, the (L/W) value of the above (i) is 5.0 or less. Further, the electrode portion 3 of the present invention has a rectangular shape on the upper surface thereof, and the arrangement pitch of the electrode portions 3 can be made fine (in particular, the pitch between the electrode portions 3 is within a range described later).

In the solder precoated substrate of the present invention, the electrode length (L) is preferably 30 to 250 μm, particularly preferably 70 to 150 μm. When the electrode length (L) is too small, when the opening 2' is provided in the insulating film 2, there is a possibility that the yield is deteriorated and the productivity of the solder precoated substrate is lowered. On the other hand, if the electrode length (L) is too long, the position of the largest projection of the solder 4 formed on the electrode portion 3 is different between the electrode portions 3a and 3b (see Fig. 4), and the contents of the single electrode portion 3 are different. It is easy to form a plurality of protrusions of the solder 4 (see FIG. 5), and it is difficult to bond the semiconductor wafer to the solder portion having such a large variation in height.

In addition, the specific range of the relevant electrode width (W) may be appropriately set so as to satisfy the above (i), and the specific range of the thickness (t) of the relevant electrode portion may be the same as the above electrode. Width (W), It is sufficient to set it as necessary to satisfy the above (ii).

In the solder precoated substrate of the present invention, the pitch between the electrode portions 3 is preferably 150 μm or less, and particularly preferably 100 μm or less. In general, the smaller the arrangement pitch of the electrode portions 3, the smaller the amount of solder formed on the electrode portion 3, and the influence of the variation in the solder height on the assemblability tends to be larger. According to the present invention, the amount of solder can be effectively suppressed. The height variation occurs, so that even fine pitches within the above range can be accommodated.

In the solder pre-coated substrate of the present invention, an electronic circuit substrate as shown in FIG. 1 is used, that is, 2' in the opening portion of the insulating film 2 covering the main surface of the substrate 1, and the plurality of fine pitches are provided to satisfy the above (i) and (ii). The substrate of the specific shape electrode portion 3 can be obtained by applying the solder paste on the electrode portion 3 of the substrate 1 and then pre-coating the molten solder on the electrode portion 3 of the substrate 1 by heating. .

When the solder paste application is performed on the electrode portion 3 of the substrate 1, for example, a screen mask in which an opening is formed in each of the electrode portions 3 on the substrate 1 is used, but is used to cover the plurality of electrode portions 3. A mesh mask having an opening formed in a wide range, and the position or shape of each electrode portion 3 is roughly ignored in a wide range including a plurality of electrode portions 3 arranged at fine pitches by screen printing or the like. The solder paste can be fully coated.

The substrate to which the solder paste has been applied is not particularly limited. For example, preheating is performed at about 150 to 200 ° C, and reflowing can be performed at a maximum temperature of about 170 to 280 ° C. The coating and smoothing heat treatment on the substrate can be carried out in the atmosphere or in an inactive environment such as N ₂ , Ar or He.

In the solder pre-coated substrate of the present invention, the solder material used in the formation of the solder layer is not particularly limited, and for example, a solder paste containing a solder powder and a flux known in the art may be used as the solder paste. A precipitation type solder paste containing a precipitation type solder material and a flux is known.

In the solder of the solder precoated substrate of the present invention thus formed, the height (the height of the largest protrusion) is usually about 10 to 20 μm, and the solder height variation between the electrode portions 3 is small. Specifically, the standard deviation (n=20) of the pre-coated solder height (i.e., the height of the largest protrusion) on the electrode portion 3 is usually preferably from 1 to 2.5, particularly preferably from 1 to 2. Further, as shown in FIG. 2 and FIG. 3, the solder formed on the solder pre-coated substrate of the present invention does not have the above problems 1) to 3), and a single protrusion portion is formed on a single electrode portion. Further, the amount of solder formed on the electrode portion will be more than the side surface.

In the assembled substrate of the present invention, the electronic components mounted on the electronic circuit board are thermocompression bonded by the solder precoated on the solder precoated substrate of the present invention.

In particular, in the assembled substrate of the present invention, it is preferable to pre-coat the main surface of the substrate and the main surface of the electronic component with the solder pre-coated on the electrode portion of the main surface of the solder pre-coated substrate (in detail, on the substrate) The electrode portion of the main surface and the electrode (bump) provided on the main surface of the electronic component are flip-chip coupled, but are not limited thereto.

When it is a flip chip coupled assembly substrate, it is preferable to exhibit a state in which an underfi11 resin is filled between the solder precoated substrate and the electronic component. That is, generally, considering the filling property of the underfill resin, the substrate is The longer the electrode length (L) is, the more advantageous it is. On the other hand, if the electrode length (L) is too long, the formed solder will have a shape as shown in Fig. 4 or Fig. 5, which tends to cause a height variation. On the other hand, in the present invention, in order to sufficiently ensure the filling property of the underfill resin, even if the electrode length (L) is set to be long, the electrode portion can be formed to satisfy the above (i) and (ii). With a shape, a solder layer having no height variation can be formed in a good shape.

[Examples]

Hereinafter, the invention will be described in detail by way of examples, but the invention is not limited to the following examples.

[Manufacturing example (modulation of solder paste)]

First, 70 parts by weight of WW grade Tall Rosin, 20 parts by weight of hexyl carbitol (solvent), and 10 parts by weight of hydrogenated castor oil (shake agent) are mixed. It is heated and melted at 120 ° C, and after cooling to room temperature, a viscous flux is prepared.

The solder powder (all of the average particle diameters of 5 μm) shown in the following (a) to (d) is used in an amount of 35 parts by weight, and 65 parts by weight of the flux prepared as described above, using a tempering mixer (THINKY) The "AWATORI RENTARO" system was subjected to kneading, and the solder pastes of the four kinds of metals shown in Table 1 were separately prepared.

(a) Sn-Ag-based solder alloy powder (Sn3.5Ag) having an Ag content of 3.5% by weight (b) Sn-Ag-Cu-based solder alloy powder (Sn3Ag0.5Cu) having an Ag content of 3.0% by weight and a Cu content of 0.5% by weight (c) Sn-containing solder alloy powder (Sn) containing 100% by weight of Sn (d) Sn-Pb system having a Sn content of 63% by weight and a Pb content of 37% by weight Solder alloy powder (63Sn37Pb)

[Examples 1 to 12 and Comparative Examples 1 to 14]

The main surface was covered with an insulating film having an opening, and the dimensions of each part (electrode length (L), electrode width (W), and electrode portion thickness (t)) were arranged at a pitch of 100 μm in the opening as shown in Table 1. And various semiconductor package substrates are produced. On the substrate, a solder paste having a metal composition shown in Table 1 was applied to a 100 μm thick screen by screen printing, and heated by a smooth heat treatment curve (ambient: oxygen concentration: 300 ppm or less) at a maximum temperature of 260° C., and then impregnated. The solder pre-coated substrate was obtained by removing the flux in an ultrasonic cleaner equipped with a butyl carbitol solution at 60 ° C.

The following evaluations were performed for each of the solder pre-coated substrates obtained as described above. The results are shown in Table 2.

<solder shape>

The solder layer formed on the solder pre-coated substrate was observed with a microscope, and the positional deviation of the maximum protrusion portion of the solder layer, the presence or absence of the presence or absence of the protrusion portion, and the formation state of the solder layer on the side surface of the electrode were confirmed, and evaluation was performed according to the following criteria.

(1) Regarding the positional deviation of the largest protrusion and the presence or absence of the protrusions in the plural: ○: The maximum protrusion is located within a range of ±10% of the electrode length (L) from the center C of the electrode portion toward the longitudinal direction of the electrode, and the protrusion There are no more than two cases (see Figure 2) ×: Non-existent "○"

(2) The state of forming the solder layer on the side surface of the counter electrode: ○: the portion where the largest protrusion of the solder formed on the electrode portion is located, and the thickness of the solder layer (solder height) in the vertical direction on the electrode portion is h, and the distance is When the thickness of the solder layer in the vertical direction of the side surface of the electrode (when the thickness of the left and right side surfaces is different, the thickness from the side surface having a larger thickness) is d, it is a case where h>d (refer to FIG. 3) ×: the above h and d system h≦d

<Standard difference between average solder height and solder height>

Using a depth of focus meter (manufactured by KEYENCE Co., Ltd.), the height of the solder layer formed on each electrode portion of the solder pre-coated substrate was measured at 20 points (measuring the position of the electrode portion of the position), and the average was calculated. Value (average solder height), standard deviation (standard deviation of solder height).

The solder pre-coated substrate, the assembled substrate, and the solder pre-coating method of the present invention are described in detail above, but the scope of the present invention is not limited to the above description, and may be appropriately carried out without departing from the gist of the present invention. Change or improve.

1‧‧‧Substrate

2‧‧‧Insulation film

2’‧‧‧ Opening

3‧‧‧Electrode

3a, 3b‧‧‧electrode

4‧‧‧ solder

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing an embodiment of a solder pre-coated substrate of the present invention, except for pre-coated solder, wherein (a) is a schematic plan view, (b) is a cross-sectional view taken along line x-x, and (c) is a y- y line cutaway view.

FIG. 2 is a schematic view showing a solder shape evaluation standard of the solder pre-coated substrate of the embodiment, and a schematic cross-sectional view of the solder when the electrode portion is cut along the longitudinal direction (when viewed from the side surface side of the electrode portion).

3 is a view for explaining a solder shape evaluation standard of the solder pre-coated substrate in the embodiment, and a schematic cross-sectional view of the solder when the portion of the largest protrusion of the solder formed on the electrode portion is vertically cut in the direction of the electrode.

4 is a view showing a position of a maximum projection of the solder 4, and a description of a conventional problem between the electrode portions 3a and 3b, and a schematic cross-sectional view of the solder 4 when the two electrode portions 3a and 3b are cut along the longitudinal direction ( a), (b).

FIG. 5 is a view for explaining a conventional problem in which a plurality of projections forming the solder 4 are formed in a single electrode portion 3, and a schematic cross-sectional view of the solder 4 when the electrode portion 3 is cut along the longitudinal direction.

FIG. 6 is a view for explaining a conventional problem in which the formation of the solder layer on the side surface of the electrode is prioritized, and the amount of solder formed on the surface of the electrode portion 3 is reduced, and the solder 4 is a schematic cross-sectional view when the electrode portion 3 is vertically cut in the longitudinal direction.

1‧‧‧Substrate

2‧‧‧Insulation film

2’‧‧‧ Opening

3‧‧‧Electrode

Claims (3)

A solder precoating method is a method in which a substrate of a plurality of electrode portions is disposed at a fine pitch in an opening portion of an insulating film covering a main surface of a substrate, and a solder paste is entirely applied to an electrode portion of the substrate, and then heated at the electrode portion. A method of performing solder pre-coating, wherein the shape of the electrode portion is set to satisfy the following shapes (i) to (iii): (i) the electrode portion has an electrode length (L) versus an electrode width ( W) has a ratio (L/W) of 6.0 or less (however, L≧W); (ii) electrode portion thickness (t) is equal to or less than electrode width (W); (iii) electrode length (L) is 30 ~250μm. The solder precoating method according to claim 1, wherein in the above (i), the ratio (L/W) of the electrode length (L) to the electrode width (W) is 5.0 or less. The solder precoating method according to claim 1, wherein the pitch between the electrode portions is 150 μm or less.