JP2005183483A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board exhibiting excellent reliability of heat resistance in which a resin layer is not stripped from a resin substrate even if a wiring board is heated to high temperatures of 250-260°C. <P>SOLUTION: Temperature at which moisture is generated through thermal decomposition of a filler contained in thermosetting resin composing a resin substrate 1 is higher than 260°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wiring board used for mounting electronic components such as semiconductor elements.

Conventionally, wiring boards used for mounting electronic components such as semiconductor elements are, for example, wiring conductor layers made of copper foil on the upper and lower surfaces of a resin board in which a glass fiber base material is impregnated with a thermosetting resin such as an epoxy resin. And a plurality of resin layers made of a thermosetting resin such as an epoxy resin and a wiring conductor layer made of copper plating are alternately laminated to form a multilayer. A part of the wiring conductor layer formed on the resin layer is exposed on the upper surface side and the lower surface side of the wiring board, and a part of the wiring conductor layer exposed on the upper surface side is electrically connected to the electrode of the electronic component via solder. A connection pad for connecting an electronic component to be electrically connected, and a connection pad for external connection in which a part exposed on the lower surface side is electrically connected to a wiring conductor of an external electric circuit board via solder doing. Then, an electronic device is mounted by joining the electrode of the electronic component and a connection pad for connecting the electronic component via solder, and the connection pad for external connection of the electronic device is connected to the external electric circuit board. By joining the wiring conductor via solder, the electrodes of the electronic component are electrically connected to the external electric circuit. In addition, in a resin substrate used for such a wiring substrate, in order to improve its flame retardancy, moisture is thermally decomposed in the thermosetting resin impregnated in the glass fiber base material by thermal decomposition of aluminum hydroxide or the like. The generated filler is contained.
JP 2003-179334 A

  By the way, in recent years, lead-free solder containing no lead has been used as a solder for connecting the solder bonding pad of the wiring board to the electrode of the electronic component and the wiring conductor of the external electric circuit board in consideration of the environment. ing. Such a lead-free solder has a higher melting point than the conventionally used lead-tin solder. Therefore, when melting the solder for joining the electrode of an electronic component or the wiring conductor of the external electric circuit board and the solder joint pad, In addition, it is necessary to heat the wiring board to a high temperature of about 250 to 260 ° C. However, when the wiring board is heated to a high temperature of about 250 to 260 ° C., it causes a problem that peeling occurs between the resin board and the resin layer laminated thereon.

  Therefore, as a result of earnest research, the present inventors have heated the wiring substrate to 250 to 260 ° C., and part of the filler contained in the thermosetting resin of the resin substrate constituting the wiring substrate is an impurity contained therein. It was found that moisture was generated by thermal decomposition under the influence of the above, and that the moisture was accumulated as a gas between the resin substrate and the resin layer on the resin substrate to separate the resin substrate and the resin layer.

  The present invention has been devised in view of such conventional problems. The purpose of the present invention is to provide a separation between a resin substrate and a resin layer even when the wiring substrate is heated to a high temperature of about 250 to 260 ° C. An object of the present invention is to provide a wiring board that does not occur and has excellent heat resistance reliability.

  The wiring board of the present invention includes a resin substrate obtained by impregnating a fiber base material with a thermosetting resin containing a filler that generates moisture by thermal decomposition, a resin layer laminated on the surface of the resin substrate, A connection pad that is electrically connected to an external conductor via solder, the wiring conductor layer being attached to the surface of the resin layer and the resin layer; The filler is characterized in that the temperature at which moisture is generated is higher than 260 ° C.

  The wiring board of the present invention is characterized in that the filler is heat-treated at a temperature of 245 to 260 ° C.

  According to the wiring board of the present invention, the temperature at which moisture due to thermal decomposition is generated from the filler contained in the thermosetting resin of the resin substrate is higher than 260 ° C., so when the lead-free solder is melted on the connection pad Even when the wiring board is heated to a high temperature of 250 to 260 ° C., moisture at the temperature is not generated from the filler contained in the thermosetting resin of the resin board. Therefore, it is possible to provide a wiring board that is excellent in heat resistance and does not cause peeling between the resin board and the resin layer thereon. Moreover, when the filler is heat-treated at 245 to 260 ° C., moisture generated at a temperature of 260 ° C. or less is favorably removed in advance by thermal decomposition of the filler.

  Next, the wiring board of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example when the best mode for carrying out the present invention is applied to a wiring board for mounting a semiconductor element. In FIG. 1, 1 is a resin substrate, 2 is a wiring conductor layer made of a metal foil, 3 is a resin layer, 4 is a wiring conductor layer made of a plating conductor, and 5 is a solder resist layer. These are mainly semiconductor elements as electronic components. A wiring board of the present invention for mounting is configured.

  The resin substrate 1 is formed, for example, by impregnating a glass fiber base material in which glass fiber bundles are woven vertically and horizontally with a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin, and a wiring conductor layer made of copper foil on the upper and lower surfaces thereof. 2 is disposed. A plurality of through holes 6 are formed from the upper surface to the lower surface of the resin substrate 1, and the inner surface of the through holes 6 is made of a copper plating film for electrically connecting the upper and lower wiring conductor layers 2. A through conductor 7 is deposited. The thermosetting resin impregnated in the glass fiber base material contains a filler such as aluminum hydroxide that is thermally decomposed at a temperature higher than 260 ° C. to generate moisture. Flame retardancy is enhanced.

  Such a resin substrate 1 is manufactured by thermally curing a sheet in which a glass fabric is impregnated with an uncured thermosetting resin, and then drilling the sheet from the upper surface to the lower surface. As the generated filler, one that has been heat-treated at a temperature of 245 to 260 ° C. is used. The wiring conductor layer 2 disposed on the upper and lower surfaces of the resin substrate 1 has a copper foil having a thickness of about 5 to 50 μm adhered to the entire upper and lower surfaces of the sheet for the resin substrate 1, and the copper foil is used as a sheet. It is formed in a predetermined pattern by etching after curing. In addition, the through conductor 7 on the inner surface of the through hole 6 is provided with a copper plating film having a thickness of about 5 to 50 μm on the inner surface of the through hole 6 by electroless plating and electrolytic plating after the through hole 6 is provided in the resin substrate 1. It is formed by precipitating.

  Further, the resin substrate 1 is filled with resin columns 8 made of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin in the through hole 6. The resin pillar 8 is for making it possible to form the resin layer 3 directly above and below the through-hole 6 by closing the through-hole 6. An uncured paste-like thermosetting resin is placed in the through-hole 6. After filling with a screen printing method and thermosetting it, the upper and lower surfaces thereof are polished to be substantially flat. The resin layer 3 is laminated on the upper and lower surfaces of the resin substrate 1 including the resin pillar 8.

  The resin layer 3 laminated on the upper and lower surfaces of the resin substrate 1 has a thickness of about 20 to 50 μm, and has a plurality of via holes 9 having a diameter of about 30 to 100 μm from the upper surface to the lower surface of each layer. A wiring conductor layer 4 made of a copper plating film is deposited on the surface and in the via hole 9. These resin layers 3 are provided to provide an insulating interval for wiring the wiring conductor layer 4 made of a copper plating film at high density. The upper wiring conductor layer 4 and the lower wiring conductor layers 2 and 4 are provided. Are electrically connected via the inside of the via hole 9 so that a high-density wiring can be formed three-dimensionally.

  For such a resin layer 3, an uncured thermosetting resin film having a thickness of about 20 to 50 μm is adhered to the upper and lower surfaces of the resin substrate 1, and the resin layer 3 is thermally cured, and via holes 9 are formed by laser processing. Further, it is formed by sequentially stacking the next resin layer 3 in the same manner. The wiring conductor layer 4 deposited in the surface of each resin layer 3 and in the via hole 9 is about 5 to 50 μm in the surface of each resin layer 3 and in the via hole 9 every time each resin layer 3 is formed. It is formed by depositing a copper plating film having a thickness on a predetermined pattern by a known pattern forming method such as a semi-additive method or a subtractive method.

  Further, a solder resist layer 5 is deposited on the outermost resin layer 3. The solder resist layer 5 is made of, for example, an insulating material in which an inorganic powder filler such as silica or talc is dispersed in an acrylic-modified epoxy resin by about 30 to 70% by mass, and improves the electrical insulation reliability between the wiring conductor layers 4 on the surface layer. At the same time, it acts to increase the bonding strength of the connection pads 4a and 4b described later to the resin layer 3.

  Such a solder resist layer 5 has a thickness of about 10 to 50 μm, and employs a roll coater method or a screen printing method to form an uncured resin paste for the solder resist layer 5 having photosensitivity as the outermost resin layer. This is formed by applying the film on the substrate 3 and drying it, and then performing exposure and development processes to form openings that expose the connection pads 4a and 4b, and then thermally curing the openings. Alternatively, after an uncured resin film for the solder resist layer 5 is stuck on the uppermost resin layer 3, it is thermally cured, and then irradiated with laser light at positions corresponding to the connection pads 4 a and 4 b. Then, the cured resin film is partially removed to form openings that expose the connection pads 4a and 4b.

  The wiring conductor layers 2 and 4 and the through conductor 7 function as conductive paths for connecting each electrode of the semiconductor element to the external electric circuit board, and are exposed on the surface of the resin layer 3 on the upper surface side. A part of the layer 4 forms a connection pad 4a for connecting an electronic component connected to each electrode of the semiconductor element via solder, and the wiring conductor layer 4 exposed on the surface of the resin layer 3 on the lower surface side. A connection pad 4b for external connection is formed, a part of which is connected to the external electric circuit board via solder.

  Further, solders 10a and 10b made of a lead-free alloy such as a tin-silver alloy or a tin-silver-copper alloy are welded to the connection pads 4a and 4b, thereby causing discoloration and oxidation of the connection pads 4a and 4b. In addition to being prevented, bonding between each electrode of the semiconductor element and the connection pad 4a via solder and bonding between the connection pad 4b and the external electric circuit board via solder are facilitated.

  Thus, in order to weld the solders 10a and 10b to the connection pads 4a and 4b, solder powder and flux made of a lead-free alloy such as a tin-silver alloy or a tin-silver-copper alloy on the connection pads 4a and 4b. A solder paste containing the above is printed and applied by using a conventionally well-known screen printing method, and the solder paste is melted by heating it at a temperature of 250 to 260 ° C.

  In the wiring board of the present invention, as described above, the temperature at which moisture due to thermal decomposition is generated from the filler contained in the thermosetting resin constituting the resin substrate 1 is higher than 260 ° C., which is important. . Since the temperature at which moisture due to thermal decomposition is generated from the filler contained in the thermosetting resin constituting the resin substrate 1 is higher than 260 ° C., the solder 10a and 10b are welded to the connection pads 4a and 4b. Even when a temperature of about 250 to 260 ° C. is applied, moisture due to thermal decomposition is not generated from the filler contained in the thermosetting resin constituting the resin substrate 1. Therefore, peeling due to moisture due to thermal decomposition of the filler does not occur between the resin substrate 1 and the resin layer 3 thereon, and a wiring substrate having excellent heat resistance reliability can be provided. When the temperature at which moisture is generated by thermal decomposition from the filler contained in the thermosetting resin constituting the resin substrate 1 is 260 ° C. or less, the wiring substrate is heated to a temperature of about 250 to 260 ° C. There is a great risk that peeling occurs between the resin substrate 1 and the resin layer 3 thereon due to moisture generated by thermal decomposition from the filler contained in the thermosetting resin constituting the resin substrate. Therefore, the temperature at which gas is generated by the thermal decomposition of the filler contained in the thermosetting resin constituting the resin substrate 1 is specified as a temperature higher than 260 ° C.

  In order to make the temperature at which moisture is generated by thermal decomposition from the filler contained in the thermosetting resin constituting the resin substrate 1 higher than 260 ° C., heat is applied at a temperature higher than 260 ° C. such as aluminum hydroxide. What is necessary is just to heat-process the filler which decomposes | disassembles and generate | occur | produces moisture beforehand at the temperature of 245-260 degreeC, and removes the water | moisture generated by thermally decomposing at the temperature of 260 degrees C or less under the influence of the impurity contained in a filler beforehand. If the temperature of the heat treatment is lower than 245 ° C., it becomes difficult to remove moisture generated by thermal decomposition at a temperature of 260 ° C. or less due to the influence of impurities contained in the filler. There is a risk that the thermal decomposition of the filler proceeds and the flame retardancy of the resin substrate 1 is reduced. Accordingly, the heat treatment of the filler is preferably performed at a temperature of 245 to 260 ° C. In addition, although a metal hydroxide is used as a filler, good flame retardancy at 260 to 300 ° C. is imparted to an epoxy resin or bismaleimide triazine resin which has a heat resistance temperature of about 260 to 300 ° C. For this purpose, aluminum hydroxide that generates moisture at 260 to 300 ° C. is preferable.

  Thus, according to the wiring board of the present invention, the electronic component is mounted on the electronic component by bonding the electrode of the electronic component and the connection pad 4a via the solder 10a. By joining to the wiring conductor of the circuit board via the solder 10b, the electrode of the electronic component is electrically connected to the external electric circuit.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing which shows the example of the best form for implementing the wiring board of this invention.

Explanation of symbols

1: Resin substrate 2, 4: Wiring conductor layer 3: Resin layers 4a, 4b: Solder bonding pads

Claims (2)

A resin substrate obtained by impregnating a fiber base material with a thermosetting resin containing a filler that generates moisture by thermal decomposition, a resin layer laminated on the surface of the resin substrate, and the surfaces of the resin substrate and the resin layer And the wiring conductor layer on the surface of the resin layer is provided with a connection pad electrically connected to an external conductor via solder, and the filler Is a wiring board characterized in that the temperature at which moisture is generated is higher than 260 ° C. The wiring board according to claim 1, wherein the filler is heat-treated at a temperature of 245 to 260 ° C.

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