JP5562550B2 - Soldering method - Google Patents

Description

  The present invention relates to a technique for depositing solder on the surface of a pad electrode for external connection provided on a wiring board. More specifically, the present invention is used for flip chip mounting of an electronic component (chip) such as a semiconductor element. The present invention relates to a solder deposition method for depositing solder on a pad electrode provided on a wiring board.

  A wiring board provided with such pad electrodes is also referred to as a “semiconductor package” for convenience in the following description in that it functions as a package for mounting a semiconductor element or the like.

  In a wiring board (semiconductor package), a pad portion (pad electrode) is defined in a required portion of the outermost wiring layer, and an electrode terminal of a semiconductor element or the like mounted on the pad electrode is provided on the pad electrode. Connected. The wiring layer is covered with an insulating layer (solder resist layer) except for the pad electrode portion. That is, a corresponding portion of the outermost insulating layer (solder resist layer) is opened, and the pad electrode is exposed from the opening. The pad electrode is arranged in a convex shape on the wiring substrate, or the surface of the pad electrode is the same surface as the substrate surface, or the electrode surface is inside the substrate surface (inside the substrate). It is formed so as to be in a position retracted.

  As means for connecting an electrode terminal (chip pad) of a semiconductor element to such a pad electrode, a solder bump is typically used. And as the formation method, while the plating method using a photo process and the vapor deposition method using a metal mask are the mainstream, on the wiring substrate in which the pad electrodes are formed at a fine interval (pitch), When solder is applied to the pad electrode, a technique called a super just method is used. This is because an adhesive layer is selectively formed only on the surface of the pad electrode, a minute solder powder (particle) is adhered thereto, and the solder powder is melted by reflow, whereby the solder is covered on the pad electrode. It is a method of wearing.

  In performing solder deposition using such a method, conventionally, the pitch of pad electrodes (distance between the electrode centers of adjacent electrodes) and electrode gaps (sides of adjacent electrodes facing each other) It was not clear what kind of particle size solder powder was used for the distance between the side surfaces), and there was no fixed standard.

An example of a technique related to such solder deposition is described in Patent Document 1 below. In the technique described here, a solder material composed of a mixture of solder particles and a liquid having a flux action is supplied onto the workpiece in a state where the solder particles are uniformly dispersed in the liquid.
JP 2006-43737 A

  The number of electrode terminals is increasing in the semiconductor elements mounted on the wiring board in order to cope with the recent increase in density and functionality, and the pitch of the electrode terminals (pad pitch) is becoming narrower. . Along with this, a technique for soldering the pad electrode on the wiring board side is also required to support a narrow pitch.

  However, as described above, when performing solder deposition using a technique called the super just method, the particle size of the solder powder to be used with respect to the electrode pitch and the electrode gap was not clear (or a certain standard) Therefore, when the electrode pitch (electrode gap) is further narrowed, a short circuit due to solder occurs between adjacent electrodes, and there is a problem that the desired narrow pitch cannot be accommodated.

  FIG. 5 is a diagram for explaining the problem. In the figure, (a) shows a state after supplying the solder powder 3 to the surface (upper surface and side surface) of the pad electrode 2 defined in a part of the wiring layer formed on the substrate (insulating layer) 1. (B) schematically shows a short circuit caused by the solder 4 between two adjacent pad electrodes 2. When the gap between the adjacent electrodes 2 and 2 becomes too narrow, when the solder powder 2 adhering to the opposite side surface of each electrode 2 is melted, it comes into contact with each other, and the solder in the contacted portion expands due to surface tension, As shown in the figure, the electrodes are short-circuited to form a bump (solder 4).

  The present invention was created in view of the problems in the prior art. When solder powder is adhered on a pad electrode, the solder powder is melted and solder is deposited on the electrode, solder between adjacent electrodes is created. It is an object of the present invention to provide a solder deposition method that can suppress the occurrence of short-circuiting and contribute to the desired narrow pitch.

To solve the above problems of the prior art, according to the present invention, the gap between the pad electrodes entire top and side surfaces of the substrate provided with a plurality of pad electrodes exposed from the resin layer was used as the experimental sample, the adjacent The relationship between the ratio (S / D) between (S) and the average particle diameter (D) of the solder powder and the occurrence rate of the short circuit due to the solder that can occur between the adjacent electrodes at the ratio is obtained by experiments. A step of preparing table data having boundary data where the incidence value decreases to 0%, and a plurality of pad electrodes whose entire upper surface and side surfaces are exposed from the resin layer, and one of the solder resist layers preparing a wiring board on which the plurality of pad electrodes in the opening are arranged, an adhesive is formed only on the upper and side surfaces of the plurality of pad electrodes of the wiring substrate, between the adjacent pad electrode of the wiring substrate From the gap between the table data, select a solder powder which the value of the ratio (S / D) had a particle size in the case three or more conditions are satisfied, the selected solder powder only the upper surface and side surfaces of the pad electrodes There is provided a solder depositing method comprising a step of selectively depositing and a step of depositing solder on the surface of the pad electrode by melting the deposited solder powder.

  According to the solder deposition method of the present invention, the table data obtained from experiments in advance (the relationship between the value of the ratio of the electrode gap to the solder particle size and the occurrence rate of shorting due to solder between adjacent electrodes is defined. The solder powder having an optimum particle diameter according to the electrode gap of the pad electrode to be soldered (the ratio is equal to or greater than a predetermined value and the occurrence rate of short circuit becomes 0%) The solder is deposited on the electrode using a solder powder having a particle size of As a result, it is possible to suppress the occurrence of a short circuit due to soldering between adjacent electrodes as seen in the prior art (FIG. 5), and as a result, it is possible to cope with a desired narrow pitch.

  Other structural features of the solder deposition method according to the present invention and unique advantages based thereon will be described in detail with reference to embodiments of the invention described below.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram for explaining table data used for carrying out a solder deposition method according to an embodiment of the present invention.

  In FIG. 1, (a) schematically shows a configuration of a substrate 10 used in the investigation described later (plan view), a wiring layer 11 including a pad electrode to be soldered, and this wiring. An insulating layer 12 formed under the layer 11 and a solder resist layer 13 formed on the wiring layer 11 and the insulating layer 12 by exposing a required portion (pad electrode) of the wiring layer 11 are provided. . Copper (Cu) is used as the material of the wiring layer (pad electrode) 11 and epoxy resin is used as the material of the insulating layer 12.

  Further, (b) shows a cross-sectional structure when viewed along the line AA in the configuration of (a), and shows a state after the solder powder 14 is supplied onto the pad electrode 11. The solder powder 14 adheres only to the surface (upper surface and side surface) of each electrode 11 as shown in the figure, and does not adhere to other portions (on the insulating layer 12). That is, the solder deposition method according to this embodiment is intended for the case where the pad electrode 11 is formed in a convex shape on the substrate 10 and the side surface is exposed together with the upper surface of the electrode 11.

  (C) shows the ratio (S / D) of the electrode gap S to the solder particle diameter D by changing the electrode gap S between the adjacent pad electrodes 11 and 11 and the average particle diameter D of the solder powder 14 in various ways. And the results of investigating the occurrence rate of shorts due to solder between adjacent electrodes. That is, the table data defining the relationship between the S / D value and the short-circuit occurrence rate obtained from the experiment is shown. This table data characterizes the present invention and is used when a soldering method is carried out as will be described later.

  As can be seen from this table data (experimental results), by using solder powder when the S / D value satisfies the condition of a predetermined value or more (in the example shown, S / D ≧ 2.92), a short circuit is achieved. This makes it possible to apply solder with reduced generation of solder. This S / D value is based solely on the experimental results, and there may be some variation and error between the individuals to be investigated. Therefore, if the condition of S / D ≧ 3 is generally satisfied, the occurrence of a short circuit will occur. It is expected that it can be suppressed.

  Incidentally, the short-circuit occurrence rate (%) shown in FIG. 1C is shown with respect to the number of pads (number of pad electrodes). In other words, a short-circuit occurrence rate of 1% means that a short-circuit occurs at one location for 100 electrodes. Therefore, if a chip having 100 pad electrodes is considered, one short circuit occurs for each chip, and this chip is rejected as a defective product.

  Next, a solder deposition method performed using the table data will be described with reference to FIGS. 2 and 3 showing an example of the process. In each process drawing, for the sake of simplicity of illustration, only the configuration of the part (pad electrode and its peripheral part) related to the present invention is shown.

  First, in the first step (see FIG. 2A), a wiring board having a pad electrode 21 to be soldered is prepared.

  Such a wiring board is, for example, a wiring board having a multilayer structure that can be formed using a build-up method, and a wiring layer made of copper (Cu) and a resin layer (insulating layer) made of an epoxy resin are alternately arranged. Each wiring layer is connected to each other through conductors (vias) stacked and filled in via holes formed in the resin layers. Further, a pad portion (two adjacent pad electrodes 21 in the illustrated example) is defined at a required portion of the outermost wiring layer. The pad electrode 21 is formed on the insulating layer (resin layer) 22. Further, a solder resist layer is formed on the wiring layer (outermost wiring layer) and the insulating layer 22 to cover the surface so that the pad electrode 21 is exposed, although not particularly illustrated. The pad electrode 21 is made of copper (Cu) as an example.

  Next, a cleaning process is performed on the surface of the wiring board prepared in this manner (on which the pad electrode 21 is formed in a convex shape). As the method, alcohol washing with ethanol, IPA (isopropyl alcohol) or the like, acid washing with dilute sulfuric acid (10% by weight) or the like is performed. Further, the surface is washed with water.

  In the next step (see FIG. 2B), the surface-cleaned wiring board is immersed in a chemical solution containing an adhesive 31 (containing components such as imidazole derivatives and benzotriazole derivatives). Since the adhesive 31 is selectively formed only on the metal (in this case, the surface of the pad electrode 21), it is not formed on the insulating layer 22. When the chemical is washed with water and dried, the adhesive 31 is selectively formed only on the surface (upper surface and side surface) of the pad electrode 21 as shown in the figure.

  In the next step (see FIG. 2C), the above-described table data (FIG. 1C) is applied to the pad electrode 21 formed on the insulating layer 22 (the adhesive 31 is formed on the surface). ), A solder powder having an optimum particle size according to the electrode gap of the pad electrode 21, that is, a solder powder 23 having a particle size satisfying the condition of S / D ≧ 3 is selected. The selected solder powder 23 is adhered to the surface of the pad electrode 21. At this time, the solder powder 23 also adheres to the insulating layer 22 as shown. As a material of the solder powder 23 to be used, for example, Sn—Ag—Cu (melting point 218 ° C.), Sn—Ag (melting point 221 ° C.), Sn—Cu (melting point 227 ° C.) or the like is used.

  In the next process (see FIG. 2D), the solder powder 23 adhered on the insulating layer 22 when the solder powder 23 is adhered in the previous process (that is, other than the portion of the pad electrode 21). Excess solder powder 23) is removed by air blow or water shower.

  In the next step (see FIG. 3A), heat treatment (200 ° C., about 30 minutes) is performed to temporarily fix the solder powder 23 adhered to the surface of the pad electrode 21 (adhesive 31). When heat treatment is performed in this step, the adhesive 31 on the pad electrode 21 is vaporized, and the solder powder 23 is directly attached (fixed) on the pad electrode 21 as shown in the figure.

  In the next step (see FIG. 3B), flux 32 as a surface treatment agent is applied to the pad electrode 21 (the solder powder 23 is temporarily fixed on the surface) formed on the insulating layer 22. To do. As the flux 32, a water-soluble flux containing halogen is used.

  In the next step (see FIG. 3C), the solder powder 23 on the pad electrode 21 is melted and bumped by reflow (at a temperature equal to or higher than the melting point of the solder for about 30 seconds) (solder 24).

  At that time, the solder powder 23 (see FIG. 3B) adhering to the opposite side surface of each adjacent electrode 21 is melted, and the melted portions (solder) approach each other. Since the solder powder 23 satisfying the above condition (S / D ≧ 3) is used, even if the molten solder swells due to surface tension, the electrodes are kept insulated from each other as shown in the figure without short-circuiting the electrodes. Bumped (solder 24).

  In the last step (see FIG. 3D), the surface is washed with water to remove the flux 32 (water-soluble flux containing halogen). Furthermore, when the surface is dried, a structure in which the solder 24 is deposited on the pad electrode 21 as shown in the drawing can be obtained.

  As explained above, according to the solder deposition method (FIGS. 1 to 3) according to this embodiment, the table data (the ratio S / D of the electrode gap S to the solder particle diameter D) obtained in advance from experiments. , And the relationship between the adjacent electrode and the rate of occurrence of a short circuit due to solder), the solder powder having an optimum particle size according to the electrode gap of the pad electrode 21 to be soldered Since the solder 24 is deposited on the electrode 21 using (solder powder 23 satisfying the condition of S / D ≧ 3), the solder between adjacent electrodes as seen in the prior art (FIG. 5) Generation | occurrence | production of the short by can be suppressed effectively. Thereby, it becomes possible to cope with a desired narrow pitch.

  In the embodiment described above, the case where the pad electrode 21 to be soldered is formed in a convex shape on the substrate and the side surface is exposed together with the upper surface of the electrode 21 has been described as an example. Of course, the form of the pad electrode is not limited to this. Depending on the usage pattern of the wiring board (semiconductor package) and the arrangement of the pad electrodes, the surface of the pad electrode may be the same as the substrate surface, or the electrode surface may be in a position retracted to the inside of the substrate surface (inside the substrate). Some are formed. The present invention can be similarly applied to these forms. Hereinafter, an example will be described.

  FIG. 4 is a view for explaining table data used for carrying out a solder deposition method according to another embodiment of the present invention.

  In FIG. 4, (a) schematically shows a configuration of a substrate 10a used for the investigation described later (plan view), a wiring layer 11a including a pad electrode to be soldered, and this wiring. And an insulating layer 12a formed so as to embed the layer 11a. As in the case of the above-described embodiment (FIG. 1), copper (Cu) is used as the material of the wiring layer (pad electrode) 11a, and epoxy resin is used as the material of the insulating layer 12a.

  Further, (b) shows a cross-sectional structure when viewed along the line AA in the configuration of (a), and shows a state after the solder powder 14 is supplied onto the pad electrode 11a. The solder powder 14 adheres only to the surface (upper surface) of each electrode 11a as shown, and does not adhere to the insulating layer 12a. That is, in the solder deposition method according to the present embodiment, the surface of the pad electrode 11a is formed so as to be flush with the surface of the substrate 10a, only the upper surface of the electrode 11a is exposed, and the side surface is not exposed. Is targeted.

  (C) is similar to the above-described embodiment (FIG. 1) in that the electrode gap S between the adjacent pad electrodes 11a, 11a and the average particle diameter D of the solder powder 14 are changed in various ways, and the electrodes The value (table data) which investigated the value of the ratio (S / D) of the space | interval S with respect to the solder particle size D, and the incidence rate of the short circuit by the solder between adjacent electrodes is shown. This table data is used when performing the solder deposition method, as in the case of the above-described embodiment. Since the method of use is the same as that described in the processing step of FIG. 2C, the description thereof is omitted here.

  As can be seen from this table data (experimental results), by using solder powder when the S / D value satisfies the condition of not less than a predetermined value (S / D ≧ 1.44 in the illustrated example), a short circuit can be achieved. This makes it possible to apply solder with reduced generation of solder. As in the case of the above-described embodiment, this S / D value is expected to have some variation and error between individuals to be investigated. Therefore, if the condition of S / D ≧ 1.5 is generally satisfied, the S / D value is short. It is expected that the occurrence of can be suppressed.

  Also in this embodiment, since the same technique as that of the solder deposition method (FIGS. 1 to 3) according to the above-described embodiment is used, the same operation effect (occurrence of occurrence of short circuit due to solder between adjacent electrodes). Suppression and response to a desired narrow pitch).

  In the embodiment of FIG. 4, the case where the surface of the pad electrode 11a is formed so as to be flush with the surface of the substrate 10a is targeted. 4), only the upper surface of the electrode is exposed and the side surface is not exposed. Therefore, the table data of FIG. 4C can be similarly applied.

It is explanatory drawing of the table data used in implementing the soldering | depositing method which concerns on one Embodiment of this invention. It is sectional drawing which shows the process (the 1) of the solder deposition method performed using the table data of FIG. FIG. 3 is a cross-sectional view showing a process (No. 2) following the process of FIG. 2. It is explanatory drawing of the table data used in order to implement the solder deposition method which concerns on other embodiment of this invention. It is a figure for demonstrating the problem in the solder deposition which concerns on a prior art.

Explanation of symbols

10, 10a ... substrate,
11, 11a, 21 ... pad electrodes (wiring layers),
12, 12a, 22 ... resin layer (insulating layer),
14, 23 ... solder powder,
24 ... solder,
31 ... adhesive,
32 ... Flux,
D: Average particle size of solder powder,
S: An electrode gap between adjacent pad electrodes.

Claims (4)

Using the substrate having a plurality of pad electrodes entire top and side surfaces are exposed from the resin layer as the experimental sample, the ratio between the average particle size of the solder powder with a gap (S) between adjacent said pad electrodes (D) Boundary at which the value of the occurrence rate is reduced to 0%, obtained from an experiment to determine the relationship between (S / D) and the occurrence rate of solder shorts that may occur between the adjacent pad electrodes at the ratio. Preparing table data having the following data;
Providing a plurality of pad electrodes whose entire upper surface and side surfaces are exposed from the resin layer, and preparing a wiring board in which the plurality of pad electrodes are arranged in one opening of the solder resist layer ;
An adhesive is formed only on the top and side surfaces of the plurality of pad electrodes of the wiring board, and the ratio (S / D) value is 3 or more from the gap between adjacent pad electrodes of the wiring board and the table data. Selecting a solder powder having a particle size when satisfying the conditions, and selectively attaching only the upper surface and side surface of the pad electrode to the selected solder powder;
Melting the adhered solder powder to deposit solder on the surface of the pad electrode. Using the substrate only the upper surface in a state in which the whole is embedded in the lower surface and the side surface into the resin layer is provided with a pad electrode exposed from the resin layer as the experimental samples, and solder gap (S) between adjacent said pad electrodes The relationship between the ratio (S / D) with the average particle diameter (D) of the powder and the occurrence rate of short circuit caused by solder that can occur between the adjacent pad electrodes at the ratio is obtained by experiment, Preparing table data having boundary data whose incidence value decreases to 0%;
Provided with a plurality of pad electrodes with only the upper surface exposed from the resin layer in a state where the entire lower surface and side surfaces are embedded in the resin layer, and the upper surface of the pad electrode and the upper surface of the resin layer are flush with each other Preparing a wiring board;
An adhesive is formed only on the upper surfaces of the plurality of pad electrodes of the wiring board, and the value of the ratio (S / D) is 1.5 or more from the gap between adjacent pad electrodes of the wiring board and the table data. Selecting a solder powder having a particle size when satisfying a condition, and selectively attaching the selected solder powder only to the upper surface of the pad electrode ;
Melting the adhered solder powder to deposit solder on the surface of the pad electrode. The step of selectively attaching the selected solder powder only to the pad electrode includes removing excess solder powder adhering to the surface of the resin layer other than the pad electrode. Item 3. The solder deposition method according to Item 1 or 2. Step of depositing solder by melting the solder powder obtained by the deposition on the surface of the pad electrode, subjected to a heat treatment for temporarily fixing the solder powder obtained by該付dressed, the pad electrode to which the solder powder is temporarily fixed 3. The solder deposition method according to claim 1, comprising: applying a reflow treatment to the solder powder to form a bump on the solder powder, and removing the flux.

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