Patent Application
20110030207
The present invention relates to a multilayer printed wiring board in which an interlayer connection is formed via inner via holes, and to a manufacturing method thereof.
In recent years, as electronic devices are becoming smaller and higher performing, there is a growing demand for providing inexpensive multilayer wiring boards that mount semiconductor chips such as LSIs at high density not only for industrial use but also for consumer use. Such multilayer wiring boards are required to electrically connect a plurality of fine pitch wiring patterns at high connection reliability.
To meet the market request, there have been proposed multilayer printed wiring boards having an interstitial via hole structure (hereinafter, IVH structure), which is easy to achieve high density wiring.
A multilayer printed wiring board having the IVH structure includes interlayer dielectric layers forming a laminated body, and via holes and through holes made of electroless plating and electroplating. The via holes electrically connect inner layer conductor circuit patterns or between inner layer conductor circuit patterns and outer layer conductor circuit patterns. The through holes connect outermost layer conductor patterns.
One of the prior arts related to the present invention is Patent Document 1 shown below.
In conventional multilayer printed wiring boards, however, the difference in the coefficient of thermal expansion between insulating material and intercalating metal causes an internal stress, which may lead to breakage of plated through holes or plated via holes especially in a substrate having a thickness of 1 mm or more. Interlayer connection is formed at a temperature of 20 to 60° C. by plating and reaches its fatigue limits due to high temperature environment or cold heat stress. It has been tried to reduce the difference in the coefficient of thermal expansion by filling the insulating resin with an inorganic filler. It is, however, difficult to make the coefficient of thermal expansion of the insulating resin lower than that of the interlayer connection material.
Patent Document 1: Japanese Patent Unexamined Publication No. 59-175796
In the multilayer printed wiring board of the present invention, when interlayer connection material has a coefficient of thermal expansion in a thickness direction lower than that of an electrically insulating substrate made of insulating material in the thickness direction, an interlayer connection of the interlayer connection material is formed at a temperature higher than the operating temperature, and the interlayer connection material is larger than the insulating material of the same wiring layer at the operating temperature in thickness.
This structure allows interlayer connection material having a lower coefficient of thermal expansion in the thickness direction than insulating material to be formed in a via hole, which is formed at a temperature higher than the operating temperature. This causes a difference in the coefficient of thermal expansion between the different materials in the thickness direction of the printed wiring board in the environment in which it is used. As a result, the internal stress always functions to contract the interlayer connecting portion. Contracting the interlayer connecting portion in this manner achieves a multilayer printed wiring board having high connection reliability.
The method for manufacturing a multilayer printed wiring board of the present invention includes: forming a via hole in insulating material; forming interlayer connection material in the via hole, the interlayer connection material having a coefficient of thermal expansion in the thickness direction lower than the insulating material; and forming interlayer connection at a temperature higher than the operating temperature of the multilayer printed wiring board, the interlayer connection being larger than the insulating material of a same wiring layer at the operating temperature in thickness.
According to the present invention, the interlayer connection material having a coefficient of thermal expansion in the thickness direction lower than the insulating material is formed in the via hole, and the interlayer connection is formed at a temperature higher than the operating temperature of the multilayer printed wiring board, the interlayer connection being larger than the insulating material of a same wiring layer at the operating temperature in thickness.
This causes a difference in the coefficient of thermal expansion between the different materials in the thickness direction of the printed wiring board in the environment in which it is used. As a result, the internal stress always functions to contract the interlayer connecting portion. Contracting the interlayer connecting portion in this manner achieves a multilayer printed wiring board having high connection reliability.
An embodiment of the present invention is described as follows with reference to drawings.
In the next step, via holes 12 are formed.
In the next step, interlayer connection material 13 is formed.
As shown in
In the next step, wiring members 14 are heated and pressurized.
Electrically insulating substrate 11 and interlayer connection material 13 that have wiring members 14 bonded thereto is cooled after the heating and pressurizing step.
This causes a difference in the coefficient of thermal expansion between the different materials in the thickness direction. As a result, the internal stress allows interlayer connection material 13 to contract, thereby improving connection reliability in via holes 12.
In the next step, wiring members 14 are patterned.
In the next step, a plurality of wiring boards are laminated.
In the next step, the wiring boards thus laminated are heated and pressurized.
In the same manner as in
In the next step, wiring members 14 are patterned.
In the embodiment, the multilayer printed wiring board is a four-layer wiring board; however, the number of the wiring layers in the multilayer printed wiring board is not limited to four. The multilayer printed wiring board has at least two wiring layers and may have five or more wiring layers laminated by the similar steps.
Multilayer printed wiring board 16 completed through the aforementioned steps is used at a temperature lower than the heating temperature used in the step of heating and pressurizing wiring members 14 shown in
In the present embodiment, the insulating material is a composite of glass woven cloth and epoxy-based resin. Alternatively, it may be a composite of either glass unwoven cloth, aramid woven cloth, or aramid unwoven cloth and thermosetting resin such as epoxy-based resin. Alternatively, it may be a composite of either glass woven cloth, glass unwoven cloth, aramid woven cloth, or aramid unwoven cloth and thermoplastic resin whose glass transition temperature is 180° C. or above. Alternatively, the insulating material may be made of a film material. Examples of the thermoplastic resin whose glass transition temperature is 180° C. or above include wholly aromatic polyester resin, polyethersulfone, polyether ketone, and polyetheretherketone.
Interlayer connection material 13 is formed by filling via holes 12 with the conductive paste. Alternatively, as long as the temperature to form the connection is higher than the operating temperature, interlayer connection material 13 may be formed in via holes 12 by filled plating, conformal plating, evaporating, or sputtering.
As described hereinbefore, according to the present embodiment, the interlayer connection material in the via holes has a coefficient of thermal expansion in the thickness direction lower than that of the insulating material in the thickness direction. The interlayer connection of the interlayer connection material is formed at a temperature higher than the operating temperature (for example, 60° C. or less) of the multilayer printed wiring board. This causes a difference in the coefficient of thermal expansion between the different materials in the thickness direction of the printed wiring board in the environment in which it is used. As a result, the internal stress allows the interlayer connecting portion to contract, thereby achieving a multilayer printed wiring board having high connection reliability.
The interlayer connection structure of the multilayer printed wiring board of the present invention provides high reliability of interlayer connection. Such multilayer printed wiring board is useful to the application relating to mounting substrates such as semiconductor packages and compact module components that are required to meet high reliability standards including minute wiring pattern and semiconductor packaging.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-101749 | Apr 2006 | JP | national |
| 2006-101750 | Apr 2006 | JP | national |
This application is a divisional of U.S. patent application Ser. No. 11/910,560, filed Oct. 3, 2007, which is a U.S. National Phase Application of PCT International Application PCT/JP2007/057394, filed Apr. 2, 2007, the entire disclosures of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11910560 | Oct 2007 | US |
| Child | 12907076 | US |
