JP2001298117A - Method for manufacturing plastic package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a plastic package capable of assuring an airtight reliability by preventing a crack of a copper plated resin board by an Au-Sn alloy for bonding a solder ball. SOLUTION: The method for manufacturing the plastic package comprises the steps of forming a profile size of a pattern for the solder ball pad to be formed at a semiconductor layer on a resin board 11 to be larger than that of the pad 15, forming a first solder resist layer 19a having an opening matched to the profile size of the pad 15 while covering an outer peripheral end of the pattern for the pad 15, executing Au-plating 18 in the opening for the pad 15, and forming a second solder resist layer 19b on an upper part of the layer 19a and an air gap after a routed wiring pattern for plating is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a solder ball pad by using a solder resist to form a solder ball pad in a process until a wiring pattern for plating exposed on a surface layer of a resin substrate is removed after plating. The present invention relates to a method of manufacturing a plastic package formed by covering an outer peripheral end of a solder ball pad pattern formed of a body layer.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become higher in performance and smaller in size, plastic packages for mounting semiconductor devices have increased the number of external connection terminals, mountability of semiconductor devices, lower cost, and heat dissipation. A ball grid array type plastic package (PBGA) is often used from the viewpoints of characteristics and low impedance. This PBGA is a single-layer or multilayer high-heat-resistant copper-clad resin made of a BT resin (a resin mainly composed of bismireimide triazine) or a polyimide resin having a conductor layer formed by stretching Cu foil on both surfaces. Using the substrate as a substrate, as shown in FIG. 3, first, (1) a through-hole is formed in a predetermined position of a copper-clad resin substrate, and (2) electroless Cu plating and electrolytic Cu are formed on the surface layer and the through-hole. (3) A dry film is adhered to a surface layer, a pattern mask is applied, and a photoresist film of the dry film formed by exposure and development is used as an etching resist film. (4) A conductor pattern is formed by etching a Cu layer made of Cu foil and Cu plating, and after removing the dry film, (5) a wire bond pad for connecting a semiconductor element. (6) A dry film is adhered, exposed and developed except for a conductive pattern portion such as a solder ball pad portion for mounting a solder ball, and a plating resist film of a photoresist film of the dry film is formed. After Ni plating and Au plating are formed in the openings of the plating resist film, the dry film, which is the plating resist film, is peeled off, and (7) a wire bond pad portion, a wiring pattern for plating, a solder ball pad portion, and the like are formed. Then, a solder resist layer is formed, and (8) the solder resist layer, Ni plating, and Au plating are etched as an etching resist film to remove the lead wiring pattern for plating.

[0003]

However, in the conventional method of manufacturing a plastic package as described above, there is still a problem in the case where a solder ball pad is formed in the process of removing a lead wiring pattern for plating after plating. There were the following problems to be solved. (1) When solder is joined to a solder ball pad, Sn of the solder component and Au of the Au plating form an AuSn alloy, and the expansion difference from the resin increases. For this reason, if the Au plating is formed up to the resin surface of the resin substrate, stress may be concentrated on the resin and cracks may occur in the resin. (2) As the above countermeasure, match the pattern of the dry film formed by Au plating with the pattern of the solder resist,
There is a method in which the Au plating is not formed up to the resin surface of the resin substrate. In this case, a pattern shift occurs, the underlying conductive layer, for example, a Cu layer is exposed, and the underlying conductive layer is peeled off by etching. (3) A void is formed after the wiring pattern for plating is removed by etching, and when the semiconductor element is mounted and the sealing resin is sealed, the void is not completely filled with the resin, resulting in poor airtight reliability. The present invention has been made in view of such circumstances, and in forming a solder ball pad in a process of removing a wiring pattern for plating after plating, an underlying conductor for forming a solder ball pad is provided. For example, the outer peripheral edge of the Cu pattern is not plated with Au to prevent cracks in the copper-clad resin substrate, and to fill the void after removing the wiring pattern for plating with a solder resist. It is an object of the present invention to provide a method of manufacturing a plastic package which ensures airtight reliability.

[0004]

According to the present invention, there is provided a method of manufacturing a plastic package according to the present invention, which comprises removing a wiring pattern for plating exposed on a surface portion of a resin substrate after a plating process. In a method of manufacturing a plastic package for forming a solder ball pad, a step of forming an outer dimension of a pattern for a solder ball pad formed of a conductor layer on a resin substrate to be larger than an outer dimension of the solder ball pad; Forming a first solder resist layer having an opening corresponding to the outer dimensions of the solder ball pad while covering the outer peripheral end of the pad pattern; and applying Au plating to the solder ball pad opening And the second solder in the upper part of the first solder resist layer and in the void after the removal of the wiring pattern for plating. And a step of forming a resist layer. Accordingly, when the solder is joined to the solder ball pad, even if the solder components Sn and Au form an AuSn alloy, the alloy layer does not reach the resin surface of the copper-clad resin substrate, so that expansion with the resin occurs. The difference does not increase. Therefore, stress does not concentrate on the resin, and cracks do not occur on the resin. Further, since it is not necessary to match the pattern of the dry film formed by the Au plating with the pattern of the solder resist, the underlying conductive layer is not exposed, and the underlying conductive layer does not peel off by etching.
Furthermore, since the voids after the wiring pattern for plating is etched by forming the second solder resist layer are filled, a highly airtight and reliable plastic package is provided when the semiconductor element is mounted and the sealing resin is sealed. can do. Here, by making the pattern formation dimension of the second solder resist layer smaller than the pattern formation dimension of the first solder resist layer, it is possible to stably place the solder ball before bonding it to the solder ball pad. it can. In addition, it is possible to absorb a pattern dimension deviation between the first and second solder resist layers.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. 1A and 1B are a side sectional view of a plastic package manufactured by applying a method of manufacturing a plastic package according to an embodiment of the present invention and a partially enlarged side section of a solder ball connection portion. FIG. 2
FIG. 2 is a partially enlarged side sectional view for illustrating a method for manufacturing a plastic package according to one embodiment of the present invention.

First, a structure of a plastic package manufactured by applying a method of manufacturing a plastic package according to an embodiment of the present invention will be described with reference to FIGS. The resin substrate 11 is made of, for example, a BT resin (a resin mainly composed of bismaileimide triazine) having a conductor layer formed by bonding Cu foils 12 on both surfaces, a polyimide resin, or the like, and has high heat resistance, dielectric properties, and insulation. It is composed of a single-layer or multilayer copper-clad resin substrate using a resin excellent in properties and workability as a base material. On both surfaces thereof, a conductor wiring pattern composed of a Cu foil 12, an electroless Cu plating 13 and an electrolytic Cu plating 14, a wiring pattern for plating, and a base for pads (wire bond pads, solder ball pads 15, etc.) are formed. A large number of solder balls 16 as connection terminal electrodes are provided on the lower surface of the resin substrate 11 by solder ball pads 15.
Is formed with a layer of Ni plating 17 and Au plating 18 interposed therebetween. On the exposed surface other than the solder balls 16, a solder resist layer 19 including a first solder resist layer 19a and a second solder resist layer 19b is formed. Also, a large number of through holes are formed by drilling and Cu plating on the resin substrate 11 to form a conductor wiring pattern on the upper surface layer, a wiring pattern for plating, a wire bonding pad, and the like, and a wiring pattern on the lower surface of the resin substrate 11. The solder balls 16 are electrically connected through the respective through holes. On the upper surface of the resin substrate 11, the bonding wires 21
The solder resist 23 is formed in a portion excluding a wire bond pad portion connected to the semiconductor element 20, a pouring opening portion used when injecting the sealing resin 22, and a plating wiring pattern portion. The semiconductor element 20 is adhered on the solder resist 24 formed in the die bonding region with an Ag paste or the like. The electrodes of the semiconductor element 20 and the wire bond pads of the resin substrate 11 are
It is made electrically conductive by a bonding wire 21 made of a u-line or the like. The semiconductor element 20 and the bonding wires 21 are sealed by transfer molding with a sealing resin 22 such as an epoxy resin.

As shown in FIG. 2, the method of manufacturing a plastic package according to one embodiment of the present invention is roughly divided into (1) a step of forming a Cu pattern for a solder ball pad, and (2) a step of forming a Cu pattern for a solder ball pad. It has a first solder resist layer forming step, (3) a solder ball pad Ni plating and Au plating forming step, and (4) a solder ball pad second solder resist layer forming step.

(1) Step of Forming Cu Pattern for Solder Ball Pad First, a resin substrate, for example, a copper-clad resin substrate 31 is prepared. The copper-clad resin substrate 31 has a single-layer or multi-layer structure made of a BT resin (a resin containing bismaileimide triazine as a main component) or a polyimide resin having a conductor layer formed by bonding Cu foils 32 on both surfaces. It is made of a heat-resistant resin substrate. The thickness of the Cu foil 32 is usually 18 to 70 μm, and copper having a purity of 99.8% or more is used. Using a single-axis drilling machine or a single-axis or multiple-axis numerical control type drilling machine (NC drill machine) for the copper-clad resin substrate 31, a hole drill made of a cemented carbide or the like is rotated at a high speed (for example, about 15,000 rpm to 100,000 rpm). degree)
Then, a through hole 33 is formed. After applying a catalyst such as palladium to the copper-clad resin substrate 31 in which the through holes 33 are formed, an electroless Cu plating film is formed in a strong alkaline bath using formalin as a reducing agent. Here, the surface layers on both surfaces of the copper-clad resin substrate 31 are electrically connected through the Cu conductor film formed on the wall surface of the through hole 33. next,
Electrolytic Cu plating is formed on the copper-clad resin substrate 31 on which electroless Cu plating has been performed. The plating tank is filled with a plating bath, for example, a copper sulfate bath, a pyrophosphoric acid bath, or the like. A copper member such as a copper plate or a copper ball attached to the anode (anode) side is filled with a cathode (cathode). It is disposed so as to face the copper-clad resin substrate 31 which is the plating object attached to the side. Further, a DC power supply device is provided between the copper member and the copper-clad resin substrate 31. By applying a voltage to the DC power supply, the copper-clad resin substrate 31 which is the object to be plated is applied.
Metal copper is deposited on the surface layer and the through hole 33 on which the electroless Cu plating is performed to form a Cu plating layer 34 composed of electroless Cu plating and electrolytic Cu plating.

Subsequently, a first dry film 35 is attached, exposed and developed to form an etching resist pattern. This is due to the photoresist method
First dry film 35 serving as an etching resist film
Is affixed onto the Cu plating layer 34. The first dry film 35 has a three-layer structure of a cover film, a photoresist, and a carrier film. It is formed on the plating layer 34. Next, the first dry film 35 made of this photoresist is covered with the wiring pattern 3.
6. Applying a pattern mask for forming the wiring pattern 37 for plating and the Cu pattern 38 for the solder ball pad and the like, performing ultraviolet exposure, and then peeling off the carrier film and developing the wiring pattern 3
6. Except for the first dry film 35 of the Cu pattern portion such as the wiring pattern 37 for plating and the Cu pattern 38 for the solder ball pad, other portions are peeled off. The remaining first dry film 35 becomes an etching resist film.

Next, the Cu plating layer 34 and the Cu foil 32 made of the electroless Cu plating and the electrolytic Cu plating are etched, and the Cu pattern such as the wiring pattern 36, the wiring pattern 37 for plating, and the Cu pattern 38 for the solder ball pad are formed.
A pattern is formed, the first dry film 35 is peeled off, and a Cu pattern is formed. In the etching in this step, the first dry film 35 is used as an etching resist film, and an etching solution such as a ferric chloride solution, a cupric chloride solution, an alkali etchant, and a hydrogen peroxide-sulfuric acid-based etchant is used. Cu plating layer 34 exposed in opening 35a of the resist film;
The foil 32 is removed by etching. After that, the first dry film 35 of the etching resist film made of the photoresist covering the Cu pattern such as the wiring pattern 36, the wiring pattern 37 for plating, and the Cu pattern 38 for the solder ball pad is sprayed with a stripping liquid on the surface. To remove and remove the photoresist by swelling and swelling the photoresist. Thereby, the wiring pattern 3
6. A Cu pattern such as a plating wiring pattern 37 and a solder ball pad Cu pattern 38 is formed. The conductor layers (Cu foil 32 and Cu plating layer 3)
Cu pattern 38 for solder ball pad formed in 4)
Are formed larger than the outer dimensions of the solder ball pad 39 described later.

(2) Step of Forming First Solder Resist Layer for Solder Ball Pad The exposed surface other than the solder ball pads 39 on the lower surface of the copper-clad resin substrate 31 and the wiring pattern 36 on the upper surface of the copper-clad resin substrate 31 Of the wire bond pad portion that connects to the semiconductor element with the bonding wire, the casting hole portion used when injecting the sealing resin that finally seals the semiconductor element to protect it from the outside, and the plating On the exposed surface excluding the routing wiring pattern 37 and the like, the first solder resist layer 40 is entirely printed by a screen printing method using a solder resist paste having a viscosity of 300 poise, a printing pressure of 35 kgf, and a screen plate of 150 mesh. It is formed by exposing and developing by photolithography. Here, the printing thickness of the first solder resist layer 40 needs to be approximately the same as the thickness of the wiring pattern 37 for plating. In addition, the solder resist layer
The printing thickness of the first solder resist layer 40 combined with a second solder resist layer 45 described later, for example, 40
By securing a thickness of about 50 μm, it corresponds to a role of not soldering in a soldering operation in a later process and a role of protecting the copper conductor surface from the external environment. In addition, using a heat-curable epoxy resin or an ultraviolet-curable acrylate resin as the solder resist polymer, various properties as a permanent mask that requires solder resist (adhesion, solder heat resistance, moisture resistance, chemical resistance) , Electrical insulation characteristics, etc.). The first solder resist layer 40 is formed so as to cover the outer peripheral end of the solder ball pad Cu pattern 38, and has an opening corresponding to the outer dimensions of the solder ball pad 39.

(3) Step of forming Ni plating and Au plating for solder ball pads Ni plating and A plating are applied to the lead wiring pattern 37 for plating.
A second dry film 41 serving as a plating resist film for preventing the u plating from being applied is stuck on the copper-clad resin substrate 31 on which the first solder resist layer 40 is formed. The second dry film 41 has a three-layer structure of a cover film, a photoresist, and a carrier film, and is adhered onto the copper-clad resin substrate 31 on which the first solder resist layer 40 is formed while peeling off the cover film. I do. Next, the second dry film 41 made of this photoresist is exposed to ultraviolet light by applying a pattern mask for forming a wiring pattern, and then, after the carrier film is peeled off, development is performed, and the wiring pattern for plating is drawn. The portion of the second dry film 41 other than the region where the 37 is formed is deleted. The remaining second dry film 41 is used as the wiring pattern 3 for plating.
It becomes a plating resist film (plating resist pattern) of No. 7.

Subsequently, the first solder resist layer 40 and the second dry film 41 are used as plating resists,
This is a step of applying Ni plating and Au plating. Solder ball pads 39 on the lower surface side of the copper-clad resin substrate 31, wire bond pads in the area of the wiring pattern 36 on the upper surface side of the copper-clad resin substrate 31, and finally, to protect the semiconductor element from the outside air. The plating wiring pattern 37 is energized through a casting hole used when a sealing resin to be sealed is injected, and electrolytic Ni plating 42 and Au are applied.
Plating 43 is applied. The Ni plating 42 is a base plating of the Au plating 43 and has a thickness of about 2 to 5 μm, and the Au plating is formed to a thickness of about 0.05 to 0.8 μm by flash plating. As the plating bath, various kinds of plating baths can be used, such as a sulfamic acid bath for nickel and a hard gold plating bath. Also,
When the Ni plating is electroless Ni plating, nickel-phosphorous plating using hypophosphorous acid is used. Further, Ni
For the plating 42, alloy plating such as NiCo plating may be used. In addition, the present invention is not limited to Ni plating, but may be any undercoating for Au plating.

Subsequently, the second dry film 41 is peeled off, and the wiring pattern 37 for plating is peeled off by etching. The second dry film 41 of a plating resist film made of a photoresist covering the routing wiring pattern 37 for plating is formed on a surface of a stripping solution, for example, 1 to 5 when the dry film photoresist is of an alkali-soluble type. A 2% aqueous solution of sodium hydroxide or potassium hydroxide is sprayed, and the photoresist is washed off while swelling, thereby removing, removing, washing, and drying. As a result, the plating wiring pattern 37 is exposed. The wiring pattern for plating 37 is formed by using the first solder resist layer 40, the Ni plating 42 and the Au plating 43 as an etching resist film, and using a ferric chloride solution, a cupric chloride solution, an alkaline etchant, and hydrogen peroxide. Using an etching solution such as a sulfuric acid-based etchant, the Cu foil 32 and the Cu plating layer 34 at the openings of the etching resist film are formed.
An etching solution is sprayed from a spray nozzle or the like onto the wiring pattern 37 for plating made of (electroless Cu plating and electrolytic Cu plating) to dissolve and remove copper.

(4) Step of Forming Second Solder Resist Layer for Solder Ball Pad The second solder resist layer is formed on the area of the void 44 where the pattern of the first solder resist layer 40 and the wiring pattern 37 for plating have been removed. The resist layer 45 is formed by printing the entire surface by photolithography, exposing and developing. Further, the pattern size of the second solder resist layer 45 is made smaller than the pattern size of the first solder resist layer 40 to absorb the pattern size deviation, so that a more accurate solder resist layer (first solder resist layer And a second solder resist layer).

[0016]

In the method of manufacturing a plastic package according to the first and second aspects of the present invention, the outer dimensions of the solder ball pad pattern formed of the conductor layer on the resin substrate are larger than the outer dimensions of the solder ball pad. Forming a first solder resist layer having an opening corresponding to the external dimensions of the solder ball pad while covering an outer peripheral end of the solder ball pad pattern; and forming an opening for the solder ball pad. Applying Au plating to the part;
Forming a second solder resist layer in the upper part of the first solder resist layer and in the void after removing the wiring pattern for plating, so that when the solder is joined to the solder ball pad, an AuSn alloy is formed. Even
The alloy layer does not reach the resin surface of the copper-clad resin substrate.
Therefore, the difference in expansion from the resin does not increase, stress is not concentrated on the resin, and the occurrence of cracks can be avoided. Also, since the voids after the wiring pattern for plating is etched with the second solder resist layer are filled, a highly airtight and reliable plastic package is provided when the semiconductor element is mounted and the sealing resin is sealed. Can be. In particular, in the method of manufacturing a plastic package according to claim 2, since the pattern size of the second solder resist layer is made smaller than the pattern size of the first solder resist layer, before the solder ball is bonded to the solder ball pad. Can be stably placed on the temporary storage. In addition, a pattern dimension deviation between the first and second solder resist layers can be absorbed, and a fine pattern can be formed.

[Brief description of the drawings]

FIGS. 1A and 1B are a side cross-sectional view of a plastic package manufactured by applying a method of manufacturing a plastic package according to an embodiment of the present invention and a partially enlarged side cross-section of a solder ball connection portion. FIG.

FIG. 2 is a partially enlarged side sectional view for explaining a method of manufacturing a plastic package according to one embodiment of the present invention.

FIG. 3 is a partially enlarged side sectional view for explaining a method of manufacturing a conventional plastic package.

[Explanation of symbols]

11: resin substrate, 12: Cu foil, 13: electroless Cu plating, 14: electrolytic Cu plating, 15: solder ball pad,
16: solder ball, 17: Ni plating, 18: Au plating, 19: solder resist layer, 19a: first solder resist layer, 19b: second solder resist layer, 2
0: Semiconductor element, 21: Bonding wire, 22: Sealing resin, 23: Solder resist, 24: Solder resist, 31: Copper clad resin substrate, 32: Cu foil, 33: Through hole, 34: Cu plating layer, 35 : First dry film, 35a: opening, 36: wiring pattern, 3
7: Leading wiring pattern for plating, 38: Cu pattern for solder ball pad, 39: Solder ball pad, 4
0: first solder resist layer, 41: second dry film, 42: Ni plating, 43: Au plating, 44:
Void, 45: second solder resist layer

Claims (2)

[Claims] In a method of manufacturing a plastic package for forming a solder ball pad in a process until a wiring pattern for plating exposed on a surface layer portion of a resin substrate is removed after a plating process, a conductive pattern is formed on the resin substrate. Forming the outer dimension of the solder ball pad pattern formed by the body layer larger than the outer dimension of the solder ball pad; and forming the solder ball pad pattern while covering the outer peripheral end of the solder ball pad pattern. Forming a first solder resist layer having an opening corresponding to the external dimensions of the pad; applying Au plating to the opening for the solder ball pad; Forming a second solder resist layer in the void after removing the wiring pattern for plating. Characteristic plastic package manufacturing method. 2. The method of manufacturing a plastic package according to claim 1, wherein the pattern size of the second solder resist layer is smaller than the pattern size of the first solder resist layer. Production method.