JP2012178482A - Manufacturing method of wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a wiring board in which a plating metal layer based on electroless plating is attached excellently onto an external connecting pad and a solder is deposited directly to a semiconductor device connecting pad.SOLUTION: While covering a central portion of a semiconductor device connecting pad 2 on an upper surface of an insulated substrate 1 with a thin film 4b of a solder resist resin layer 4, a plating metal layer 6 is attached to an exposed central portion of an external connecting pad 2 on a lower surface of the insulated substrate 1 by electroless plating. Next, the thin film 4b of the solder resist resin layer 4 at an upper surface side of the insulated substrate 1 is removed, the central portion of the semiconductor device connecting pad 2 is exposed and finally, a solder 7 is deposited to the exposed central portion of the semiconductor device connecting pad 2.

Description

  The present invention relates to a method for manufacturing a wiring board used for mounting a semiconductor element.

  Conventionally, a wiring board used for mounting a semiconductor element such as a semiconductor integrated circuit element includes, for example, an insulating board made of a glass-epoxy board or the like, and an insulating board in which a plurality of insulating layers made of epoxy resin are laminated and A wiring conductor made of copper such as a copper foil or a copper plating film is disposed on the surface. In addition, a plurality of semiconductor element connection pads are formed in the central portion of the upper surface of the insulating substrate, to which the electrodes of the semiconductor element are electrically connected via solder bumps, and the wiring conductor of the external electric circuit substrate is formed on the lower surface of the insulating substrate. External connection pads that are electrically connected via solder balls are formed. Furthermore, solder resist layers having openings exposing the central part of each semiconductor element connection pad and the central part of each external connection pad are provided on the upper and lower surfaces of the insulating substrate. The outer peripheral part of each semiconductor element connection pad and the outer periphery of each external connection pad It is attached so as to cover the part. The semiconductor element connection pad and the external connection pad exposed from the solder resist layer include a nickel-gold plating layer, a nickel plating layer, a palladium plating layer, and a gold plating layer in which a nickel plating layer and a gold plating layer are sequentially deposited. A plating metal layer composed of a nickel-palladium-gold plating layer or the like on which is sequentially deposited is deposited. Furthermore, solder bumps for connecting to the electrodes of the semiconductor element are welded to the semiconductor element connection pads. Alternatively, solder bumps may be welded directly on the semiconductor element connection pads or solder layers may be welded directly on the external connection pads without depositing the plated metal layer on the semiconductor element connection pads and the external connection pads. is there.

  Then, the electrodes of the semiconductor element are brought into contact with the solder bumps welded to the semiconductor element connection pads, and the solder bumps are heated and melted to electrically connect the semiconductor element electrodes and the semiconductor element connection pads via the solder bumps. The semiconductor element is mounted on the wiring board by injecting a sealing resin called underfill into the gap between the semiconductor element and the wiring board and curing it. Also, the solder balls are deposited on the external connection pads by placing the solder balls on the plated metal layer or the solder layer deposited on the external connection pads and heating and melting the solder balls. By heating and melting the ball in contact with the wiring conductor of the external electric circuit board, the wiring board is mounted on the external electric circuit board via the solder balls.

  Recently, in a wiring board for mounting a semiconductor element as described above, in consideration of the environment, as a solder bump welded to a semiconductor element connection pad or a solder ball welded to an external connection pad, lead is used. So-called lead-free solders such as tin-silver alloys and tin-silver-copper alloys that are not included have come to be used. However, when this lead-free solder is used as a solder bump for connecting the electrode of the semiconductor element and the semiconductor element connection pad, the semiconductor element is connected to the semiconductor element connection pad via the solder bump. When a current for operating the semiconductor element flows between the electrode and the semiconductor element connection pad at a high current density for a long time, a void due to electromigration may occur in the solder bump. When a void due to electromigration occurs in the solder bump, the electrical resistance between the electrode of the semiconductor element and the semiconductor element connection pad connected thereto increases, or the electrode of the semiconductor element is connected to the electrode. The semiconductor element cannot be normally operated due to electrical disconnection between the semiconductor element connection pads and the like. Electromigration that occurs in such solder bumps is particularly the case when solder bumps are welded via a plated metal layer made of nickel, rather than when solder bumps are welded directly onto a semiconductor element connection pad made of copper. It occurs remarkably. Therefore, when solder bumps made of lead-free solder are welded to the semiconductor element connection pads made of copper, it is preferable to weld the solder bumps directly on the semiconductor element connection pads.

  On the other hand, it is preferable that a plating metal layer including a nickel plating layer is applied to the external connection pads as a base for welding solder balls. This is because when solder made of lead-free solder is directly welded on an external connection pad made of copper, after mounting the wiring board on the external electric circuit board, an external impact is applied between them. This is because breakage at the joint between the two tends to occur. When a plated metal layer including a nickel plating layer is deposited on the external connection pad made of copper, the impact resistance for satisfactorily withstanding such an impact is enhanced. Note that the area of the external connection pad is about 10 to 100 times larger than that of the semiconductor element connection pad. Therefore, the current density per unit area is 10 to 1/100 that of the semiconductor element connection pad. Since the current is much smaller, even if a current flows between the external connection pad and the external electric circuit board for a long time, the risk of voids due to electromigration in the solder balls connecting the two is extremely small. . Therefore, it is not necessary to weld solder directly on the external connection pad made of copper.

  By the way, in order to obtain a wiring substrate in which solder bumps are directly welded to the semiconductor element connection pads and a plating metal layer such as nickel-palladium-gold plating is applied to the external connection pads, it will be described below. A method is conceivable. First, a semiconductor element connection pad is formed on the upper surface of the insulating substrate, and an external connection pad is formed on the lower surface of the insulating substrate. Next, a photosensitive solder resist resin layer is deposited on the upper and lower surfaces of the insulating substrate so as to cover the semiconductor element connection pads and the external connection pads, respectively. Next, the solder resist resin layers on the upper and lower surfaces of the insulating substrate are exposed and developed, and then UV-cured and thermally cured to expose the central portion of the semiconductor element connection pad on the upper surface of the insulating substrate. And forming a lower side solder resist layer having an opening exposing the central portion of the external connection pad on the lower surface of the insulating substrate. Next, a plating resist layer is laminated so as to cover the semiconductor element connection pad only on the solder resist layer on the upper surface side, and the plating metal layer is electrolessly formed on the surface of the external connection pad exposed from the solder resist layer on the lower surface side. Deposit by plating. Finally, the plating resist layer is peeled off and removed from the solder resist layer on the upper surface side, and solder bumps are welded onto the semiconductor element connection pads exposed from the solder resist layer.

  However, according to this method, the plating resist layer is laminated so as to cover the semiconductor element connection pad on the solder resist layer on the upper surface side, and the plating metal is exposed on the surface of the external connection pad exposed from the solder resist layer on the lower surface side. When depositing the layer by the electroless plating method, the plating resist layer is attacked by the electroless plating solution and eluted into the electroless plating solution to decompose the electroless plating solution or to cover the surface of the external connection pad. The plated metal layer to be deposited cannot be deposited well. This is because the electroless plating solution exhibits strong alkalinity and is at a high temperature, and the plating resist is given the property of being easily attacked by the alkaline stripping solution in order to ensure the peelability from the object to be plated. is there. Therefore, a wiring board in which a solder bump is directly welded to a semiconductor element connection pad by such a method and a plating metal layer such as nickel-palladium-gold plating is attached to the external connection pad by an electroless plating method. It is difficult to get.

JP 2005-191131 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor element made of copper provided on the upper surface of an insulating substrate, while an external connection pad made of copper provided on the lower surface of the insulating substrate is well coated with a plated metal layer by an electroless plating method. An object of the present invention is to provide a method of manufacturing a wiring board in which solder is directly welded to a connection pad.

According to the method for manufacturing a wiring board of the present invention, a semiconductor element connection pad to which an electrode of a semiconductor element is connected is formed on an upper surface of an insulating substrate, and an external connection pad to be connected to an external electric circuit board is formed on the lower surface of the insulating substrate And a process of
Applying a photosensitive solder resist resin layer to the upper and lower surfaces of the insulating substrate so as to cover the semiconductor element connection pads and the external connection pads;
The solder resist resin layer having photosensitivity is selectively unexposed to a portion corresponding to the center portion of the semiconductor element connection pad and a portion corresponding to the center portion of the external connection pad in the solder resist resin layer. A step of exposing so that a portion other than the unexposed portion is exposed;
In the exposed solder resist resin layer, the exposed part remains as it is, and a part of the unexposed part becomes a thin film thinner than the exposed part, and the central part of the semiconductor element connection pad and Step of curing the developed solder resist resin layer after developing so as to cover the central portion of the external connection pad, and
Removing the thin film of the cured resin layer for solder resist only on the lower surface side of the insulating substrate to expose the central portion of the external connection pad; and
A step of depositing a plating metal layer by an electroless plating method on the exposed central portion of the external connection pad while the central portion of the semiconductor element connection pad is covered with the thin film;
Removing the thin film in the solder resist resin layer on the upper surface side of the insulating substrate to expose a central portion of the semiconductor element connection pad;
A step of welding solder to the exposed central portion of the semiconductor element connection pad;
It is characterized by performing.

  According to the method for manufacturing a wiring board of the present invention, the lower surface side of the insulating substrate with the central portion of the semiconductor element connection pad formed on the upper surface side of the insulating substrate covered with the hardened thin film of the solder resist resin layer. When the plated metal layer is deposited on the external connection pad, the central portion of the external connection pad formed on the surface is exposed and the plated metal layer is deposited on the exposed central portion of the external connection pad by electroless plating. Since the semiconductor element connection pad is covered with a thin film obtained by curing the solder resist resin layer, the plated metal layer can be selectively applied only to the external connection pad. In this case, since the thin film of the solder resist resin layer covering the central portion of the semiconductor element connection pad is cured and the crosslinking of the resin component is proceeding, even in the electroless plating solution exhibiting strong alkalinity, Therefore, the plated metal layer can be satisfactorily applied to the external connection pads by the electroless plating method. In addition, after depositing the plating metal layer on the external connection pad, the thin film of the solder resist resin layer on the semiconductor element connection pad is removed, and solder is welded to the exposed central part of the semiconductor element connection pad. Solder can be directly deposited on the semiconductor element connection pad made of copper.

FIG. 1 is an enlarged schematic cross-sectional view of a main part for each process for explaining a method for manufacturing a wiring board according to the present invention.

  Next, an example of an embodiment of the method for manufacturing a wiring board according to the present invention will be described with reference to FIGS. 1 (a) to 1 (h). First, as shown in FIG. 1A, a semiconductor element connection pad 2 to which an electrode of a semiconductor element is electrically connected is formed on the upper surface of the insulating substrate 1 and wiring of an external electric circuit board is formed on the lower surface of the insulating substrate 1. External connection pads 3 that are electrically connected to the conductor are formed.

  The insulating substrate 1 is a flat plate formed by laminating a plurality of insulating layers made of, for example, a glass-epoxy plate or an epoxy resin, and has an internal wiring conductor (not shown) made of a copper foil or an electroless and electrolytic copper plating layer. ) Is formed.

  The semiconductor element connection pad 2 and the external connection pad 3 are each formed of a copper foil or an electroless and electrolytic copper plating layer having a thickness of about 10 to 30 μm, and are formed by a conventionally known subtractive method or semi-additive method. The semiconductor element connection pad 2 has a diameter of about 50 to 100 μm, and the external connection pad 3 has a diameter of about 300 to 1000 μm.

  Next, as shown in FIG. 1B, the solder resist resin layers 4 and 5 having photosensitivity are covered so as to cover the semiconductor element connection pads 2 and the external connection pads 3 on the upper and lower surfaces of the insulating substrate 1. Put on. The solder resist resin layers 4 and 5 have a thickness of about 10 to 20 μm on the semiconductor element connection pad 2 and the external connection pad 3.

  Next, as shown in FIG. 1C, the solder resist resin layers 4, 5 having photosensitivity are arranged between a portion corresponding to the central portion of the semiconductor element connection pad 2 in the solder resist resin layers 4, 5 and the outside. The part corresponding to the central part of the connection pad remains selectively as unexposed parts 4a and 5a, and exposure is performed so that parts other than the unexposed parts 4a and 5a are exposed. At the time of exposure, the portions corresponding to the unexposed portions 4a and 5a do not transmit ultraviolet rays, and the other portions are exposed to ultraviolet rays on the solder resist resin layers 4 and 5, respectively. A method is adopted in which they are arranged so as to face each other, and the portions other than the unexposed portions 4a and 5a are irradiated with ultraviolet rays through the mask to be exposed.

  Next, as shown in FIG. 1D, the exposed solder resist resin layers 4 and 5 remain exposed as they are and the unexposed portions 4a and 5a are partially exposed from the exposed portions. The thin films 4b and 5b are developed so as to cover the central portion of the semiconductor element connection pad 2 and the central portion of the external connection pad 3 so as to remain. For development, an alkaline developer containing sodium carbonate is used. The thickness of the thin films 4b and 5b remaining covering the central portion of the semiconductor element connection pad 2 and the central portion of the external connection pad 3 is about 0.5 to 2.0 μm. In order to leave the thin films 4b and 5b having such a thickness, the developing time is shortened from the normal time, the temperature of the developing solution is decreased from the normal level, or the concentration of the developing solution is decreased from the normal level. By developing these operations singly or in combination, the unexposed portions 4a and 5a are not removed completely, and 0.5 to 2.. It is possible to form thin films 4b and 5b having a thickness of 0 μm.

  Next, the developed solder resist resin layers 4 and 5 are cured. For curing, ultraviolet curing and thermal curing are used. In the case of ultraviolet curing, the entire surface of the solder resist resin layers 4 and 5 is irradiated with ultraviolet rays. In the case of thermosetting, the solder resist resin layers 4 and 5 are heated to a temperature higher than the thermosetting temperature. Thermal curing may be performed after ultraviolet curing, or ultraviolet curing may be performed after thermal curing. The resin layers 4 and 5 for the solder resist have a strong alkali resistance due to the progress of crosslinking of the resin component contained by the curing.

  Next, as shown in FIG. 1E, the thin film 5 b in the cured solder resist resin layer 5 on the lower surface side is removed to expose the central portion of the external connection pad 3. For removing the thin film 5b, for example, a wet blast method is used. Specifically, a method of spraying abrasive grains made of alumina or the like together with water at high pressure on the entire surface of the solder resist resin layer 5 on the lower surface side until the thin film 5b covering the central portion of the external connection pad 3 disappears is employed. By this spraying, the surface of the solder resist resin layer 5 on the lower surface side is thinly scraped off and the thin film 5b can be removed. At this time, the thin film 4 b in the solder resist resin layer 4 on the upper surface side is left while covering the central portion of the semiconductor element connection pad 2. In addition, after removing the thin film 5b, it is preferable to clean the exposed surface of the external connection pad 3 by thin etching with an etching solution containing hydrogen peroxide and sulfuric acid.

  Next, as shown in FIG. 1F, a plated metal layer 6 is formed on the exposed surface of the external connection pad 3 by an electroless plating method. The plating metal layer 6 is preferably a nickel-palladium-gold plating layer in which a nickel plating layer, a palladium plating layer, and a gold plating layer are sequentially deposited. The nickel plating layer is formed by using an electroless nickel-phosphorous plating solution containing, for example, nickel sulfate and sodium citrate, sodium acetate, sodium hypophosphite, ammonium chloride, and the like to form phosphorus 3 on the exposed surface of the external connection pad 3. It deposits by depositing the electroless nickel plating layer which contains about 10 mass%. The thickness of the electroless nickel plating layer is preferably in the range of 0.5 to 10 μm. The palladium plating layer is, for example, a reduced electroless material containing 2 to 5% by mass of phosphorus on the nickel plated layer using a reduced electroless palladium-phosphorous plating solution containing tetraamminepalladium chloride, ethylenediamine, sodium hypophosphite and the like. Deposited by depositing a palladium plating layer. The thickness of the palladium plating layer is preferably in the range of 0.01 to 0.2 μm, particularly preferably in the range of 0.03 to 0.1 μm. The gold plating layer is, for example, a substitution reduction type electroless gold plating on a palladium plating layer using a substitution reduction type electroless gold plating solution containing potassium gold cyanide and potassium hydroxide, sulfonate, potassium cyanide, amino alcohol, etc. Deposited by depositing a layer. The thickness of the gold plating layer is preferably in the range of 0.01 to 0.5 μm. The plated metal layer 6 may be a nickel-gold plated layer in which a nickel plated layer and a gold plated layer are sequentially deposited.

  At this time, since the semiconductor element connection pad 2 on the upper surface side is covered with the hardened thin film 4b of the solder resist resin layer 4, the plated metal layer is not attached to the semiconductor element connection pad. In addition, although the plating solution for depositing the plating metal layer 6 exhibits strong alkalinity, the thin film 4b covering the central portion of the semiconductor element connection pad 2 is cured and the crosslinking of the resin component is proceeding. Therefore, the plating metal layer 6 can be satisfactorily adhered to the external connection pad.

  Next, as shown in FIG. 1G, the thin film 4b in the cured solder resist resin layer 4 on the upper surface side is removed to expose the central portion of the semiconductor element connection pad 2. For the removal of the thin film 4b, for example, a wet blast method is used as in the case of the thin film 5b. Specifically, a method is adopted in which abrasive grains made of alumina or the like are sprayed together with water at high pressure on the entire surface of the solder resist resin layer 4 on the upper surface side until the thin film 4b covering the central portion of the semiconductor element connection pad 2 disappears. . By this spraying, the surface of the solder resist resin layer 4 on the upper surface side is thinly scraped off and the thin film 4b is removed. In addition, after the removal of the thin film 4b, it is preferable to clean the exposed surface of the semiconductor element connection pad 2 by thin etching with an etching solution containing hydrogen peroxide and sulfuric acid.

  Finally, as shown in FIG. 1H, the wiring board according to the present invention is completed by directly welding solder bumps 7 made of lead-free solder on the exposed semiconductor element connection pads 2. In order to weld the solder bumps 7 to the semiconductor element connection pads 2, a solder paste is printed on the semiconductor element connection pads 2 by a screen printing method and then reflowed, or solder balls are mounted on the semiconductor element connection pads. Then, a reflow method is adopted.

  Thus, according to the method for manufacturing a wiring board of the present invention, the plated metal layer by the electroless plating method is satisfactorily applied to the external connection pad made of copper provided on the lower surface of the insulating substrate, and the upper surface of the insulating substrate. It is possible to provide a wiring substrate in which solder is directly welded to a semiconductor element connection pad made of copper.

DESCRIPTION OF SYMBOLS 1 Insulation board | substrate 2 Semiconductor element connection pad 3 External connection pad 4,5 Solder resist resin layer 4a, 5a Unexposed part 4b, 5b Thin film 6 Plating metal layer 7 Solder

Claims (1)

Forming a semiconductor element connection pad connected to the electrode of the semiconductor element on the upper surface of the insulating substrate and forming an external connection pad connected to the external electric circuit substrate on the lower surface of the insulating substrate;
Applying a photosensitive solder resist resin layer to the upper and lower surfaces of the insulating substrate so as to cover the semiconductor element connection pads and the external connection pads;
The solder resist resin layer having photosensitivity is selectively unexposed to a portion corresponding to the center portion of the semiconductor element connection pad and a portion corresponding to the center portion of the external connection pad in the solder resist resin layer. A step of exposing so that a portion other than the unexposed portion is exposed;
In the exposed solder resist resin layer, the exposed part remains as it is, and a part of the unexposed part becomes a thin film thinner than the exposed part, and the central part of the semiconductor element connection pad and Step of curing the developed solder resist resin layer after developing so as to cover the central portion of the external connection pad, and
Removing the thin film of the cured resin layer for solder resist only on the lower surface side of the insulating substrate to expose the central portion of the external connection pad; and
A step of depositing a plating metal layer by an electroless plating method on the exposed central portion of the external connection pad while the central portion of the semiconductor element connection pad is covered with the thin film;
Removing the thin film in the solder resist resin layer on the upper surface side of the insulating substrate to expose a central portion of the semiconductor element connection pad;
A step of welding solder to the exposed central portion of the semiconductor element connection pad;
A method for manufacturing a wiring board, comprising:

Images