Patent Application
20080099235
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-296924, filed Oct. 31, 2006, the entire contents of which are incorporated herein by reference.
1. Field
One embodiment of the present invention relates to a printed-wiring board having electrodes on which a semiconductor device is to be flip-chip-bonded, each of the electrodes being formed at an exposed portion of a wiring pattern defined by a solder resist coating film.
2. Description of the Related Art
In a small-sized electronic equipment to be easily carried, a technique for mounting a semiconductor device such as a bare chip on a circuit board inside the equipment by flip-chip bonding has become widely used. As to a printed-wiring board used in a circuit board, a printed-wiring board having electrodes to be used for flip-chip bonding is used, in which the electrodes are formed at an exposed portion of a wiring pattern defined by the solder resist coating film. In the printed-wiring board coated with the solder resist coating film is provided with a wiring pattern area in which a plurality of wiring patterns arranged in a prescribed direction are exposed to form an electrode forming part for the flip-chip bonding. The exposed wiring patterns used as the electrodes are applied with plating using a metal such as Ni/Au alloy and Sn, if necessary.
The exposed electrodes thus formed each has a rectangle shape with a short side corresponding to a width of a wiring. Therefore, when an IC chip is flip-chip-bonded onto a printed-wiring board provided with the electrodes each having the rectangle shape, a solder bump of the IC having a ball like shape for example, will be deformed into a rectangle shape corresponding to that of the electrode. The short side of the bump is deformed in accordance with the wiring-width direction and a long side thereof is elongated along a line length direction of the wiring, so that the shape in the wiring width is relatively thinner (narrower) than that of in the line length direction. Accordingly, a bonding area or a wet-spreading area of the solder in the wiring width direction becomes extremely smaller than that in the line length direction. In other words, a bonding area or a wet-spreading area of the solder on a passivation side of the IC chip and that on the electrode side of the printed-wiring board become extremely different from each other.
In general, the long-term bonding reliability of a solder bonding part of a semiconductor component will be decreased due to the accumulation of the stress caused by a change in temperature of a surrounding environment, although the bonding part is reinforced with a buffer material such as an under-fill resin provided under the IC chip. The stress is generated due to a difference in thermal expansion coefficient between a silicon part of the IC chip and a resin part of the printed-wiring board. The accumulation of the stress will cause an occurrence of a clack at the solder bonding part. In this case, since the shapes of the solder bumps are different in a length direction and a width direction of wiring acting as the electrode, and the bonding or the wet-spreading areas of the solder on the passivation side of the IC chip and on the electrode side of the printed-wiring board are extremely different from each other, the vicinity of the solder bump bonding at the side of the passivation of the IC chip becomes weak against the thermal stress.
As for a technique coping with such a defect, there is a technique to form a solder pad shape of the printed-wiring board so that the central part of the solder pad is heaped. This technique is applicable to a semiconductor device of a type in which an IC chip such as a QFP is coated with a mold resin, but hard to apply it to mount a bare chip which requires electrode processing for forming electrodes arranged with a microscopic pitch. For example, Jpn. Utility Model Appln. KOKAI Publication No. 5-28073 teaches such a technique.
As mentioned above, the printed-wiring board is provided with the electrodes on which a semiconductor device is bonded in a flip-chip manner. The electrodes are formed at the exposed part of the wiring pattern defined by the solder resist coating film. Since the shape of the solder bumps is different in the solder wet-spreading area on the passivation side of the IC chip and on the electrode side of the printed-wiring board from each other, the difference therebetween poses a subject of a flip-chip bonding technique such that the passivation of the IC chip and the vicinity of the solder bump bonding become weak with respect to heat stress.
According to one aspect of the present invention, there is provided a printed-wiring board on which electrodes for semiconductor device bonding in a flip-chip-mounted manner are formed at an exposed part of a wiring pattern defined by a solder resist coating film, wherein the electrodes each includes an expanded section spreading in a line width direction of the wiring pattern to form the electrode at which the semiconductor device is bonded.
Another aspect of the present invention is a method for forming an electrode of a printed wiring board on which an electrode for semiconductor device bonding to be flip-chip-mounted is formed by an exposed section of a wiring pattern defined by a solder resist coating film, comprising forming the electrode for semiconductor device by disposing an expanded section spreading in a line width direction of the wiring pattern at the electrode, and by including the expanded section.
Still another aspect of the present invention is a hard disk device comprising a recording medium; a drive mechanism to rotation-drive the recording medium; a magnetic head to write data in the recording medium and read out the data from the recording medium; a drive mechanism to position-control the magnetic head; and a circuit substrate to control each of the drive mechanism, wherein the circuit substrate is configured so that it includes a component mounting unit on which a semiconductor device to be flip-chip-mounted is mounted, and so that an electrode of the component mounting unit is formed by an exposed section of a wiring pattern defined by a solder resist coating film, and the electrode includes an expanded section formed at the exposed section by protruding in a direction crossing a length direction of an exposed wiring pattern.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings.
An embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.
A hard disk device 8 is configured to include a device main body 10, and a control circuit board 11.
The main body 10 includes a case 17 having an upper wall 17a, a lower wall 17b, and a side wall 17c, and a magnetic disk 21, a spindle motor 22, a magnetic head 23, a head actuator 24, a voice coil motor 25, etc., stored in the case 17.
The control circuit board 11 has engaging halls h which engage with protruded parts (not shown) protruded from the lower wall 17b of the main body 10, and is mounted on the exterior lower surface part of the case 17 in a state in which the engaging halls h are engaged with the protruded parts of the lower wall 17b.
The control circuit board 11 houses a functional circuit, which controls hardware stored in the case 17, writes data in the magnetic disk 21 with the magnetic head 23, and reads out the data from the magnetic disk 21. As for one constituent element of the functional circuit, a semiconductor device 20 of a bare chip structure is mounted in a flip-chip manner to be disposed on a prescribed component mounting section PB on the control circuit board 11.
The control circuit board 11 provided with the component mounting section PB is structured by using a printed-wiring board according to one embodiment of the present invention.
As shown in
The electrodes 12 each has, as shown in
The shape of the electrode 12 is determined so that the electrode 12 has the shape and the area corresponding to a shape and an area of an under bump metal 20b mounted in an opening of the passivation 20a formed on the under surface of the IC chip 20 as shown in
As shown in
Therefore, as can be seen from
According to the embodiment given above, although the shape of the expanded section 12a of the electrode 12 is made circular so as to match the passivation opening, an expanded pattern structure of a polygon expanded section may be used. For example, a combination of the wiring pattern 12p and a hexagon expanded section 12b to form a pattern shape as shown in
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-296924 | Oct 2006 | JP | national |
