Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2002-10-02
2004-04-27
Ho, Hoai (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
Reexamination Certificate
active
06727595
ABSTRACT:
TECHNICAL FIELD
This invention relates to a semiconductor device, a method of making the same, a circuit board, and a flexible substrate, and, in particular, to a semiconductor device, a method of making the same, a circuit board, and a flexible substrate in which a flexible substrate is disposed above an active surface of a semiconductor chip.
BACKGROUND OF ART
If high-density mounting of semiconductor devices is pursued, bare-chip mounting would be ideal. However, quality assurance and handling are difficult in the bare chip state. To that end, a semiconductor device has been proposed in which a bare chip is packaged to form a package of a size that is close to the size of the bare chip, as disclosed in, for example, International Publication WO95/08856.
This semiconductor device is made as described below. A flexible substrate (abbreviated to substrate) is disposed above the active surface of a semiconductor chip. External electrodes for mounting are provided on this flexible substrate. Leads provided on the flexible substrate are then connected to electrodes of the semiconductor chip while being cut, and a resin in gel form is injected between the semiconductor chip and the flexible substrate to complete the semiconductor device.
With this semiconductor device, inspections can be done reliably in the packaged state, it is possible to ensure product quality because the resin between the semiconductor chip and the flexible substrate covers the active surface of the semiconductor chip, and handling is also easy.
However, with this technique, the leads must be cut one by one and bonded one by one (single-point bonding). If an attempt is made to cut and connect all of the leads at the same time, the support of the flexible substrate disappears and therefore the connection positions of the leads and the electrodes are placed at different positions. This means that the technique disclosed in the above Publication cannot be applied to a batch connection method for all of the leads. This is inferior to batch connections (gang bonding) from the mass production viewpoint.
In addition, since the substrate itself is flexible, various problems caused by flection of the substrate cannot be solved. For example, when the resin in gel form is injected between the semiconductor chip and the substrate, there is a strong possibility that the injection will be uneven, because of this flection. In addition, the external electrodes are positioned on the top of the flexible substrate, so that it is not possible to fix the positions thereof absolutely, and difficulties are likely to occur, particularly during the connection to the external substrate.
In addition, a flexible substrate has to be held by a special jig positioned so as to surround the semiconductor chip, and that jig must be prepared anew.
The present invention was devised in order to solve the above described problems and its objective is to prepare a semiconductor device, a method of making the same, a circuit board, and a flexible substrate that are easy to assure the quality and easy to handle, and are extremely reliable during fabrication.
This invention further provides a semiconductor device, a method of making the same, a circuit board, and a flexible substrate that have superlative mass production capabilities and enable the use of existing fabrication devices without modification in the fabrication thereof.
DISCLOSURE OF INVENTION
A method of making a semiconductor device in accordance with this invention comprises:
a step of preparing a flexible substrate that has a region overlapping a semiconductor chip, the flexible substrate having external electrode formation portions where external electrodes are formed, the external electrode formation portions are formed within the overlapped region;
a step of providing a gap preservation member on at least one of a surface having electrodes of the semiconductor chip and a surface of the flexible substrate that is disposed facing the surface having electrodes of the semiconductor chip; and
a step of arranging the semiconductor chip and the flexible substrate with surfaces thereof facing one another, in a state in which the gap preservation member is interposed therebetween, and connecting connection portions formed on the flexible substrate to the electrodes of the semiconductor chip.
With this invention, the preparation of the above-described flexible substrate makes it possible to provide a package that is of the same size as the chip. In this state, a surface of a semiconductor chip having electrodes is arranged so as to face a surface of a flexible substrate that is disposed facing that surface of the semiconductor chip having electrodes, in other words, a surface of the flexible substrate on a side on which connection portions to electrodes are positioned. A gap preservation member is provided on at least one of these surfaces. Since the semiconductor chip and the flexible substrate are arranged with the gap preservation member therebetween, a gap can be guaranteed reliably between the two components. This makes it unnecessary to provide a jig for preserving this gap. Since this constant gap is held between the two components from the step of assembling the semiconductor chip and the flexible substrate onward, unexpected electrical short between the two components can be prevented. In addition, the connection portions of the flexible substrate and the electrodes of the semiconductor chip are connected together in a state in which the gap preservation member is interposed therebetween, so that the gap preservation member acts as a support shaft during the connection, enabling reliable connection.
The gap preservation member formed during the step of providing the gap preservation member is preferably provided within a region that excludes a region corresponding to the external electrode formation portion. In other words, the gap preservation member is not provided in a part corresponding to the external electrode formation portion for the formation of external electrodes. This ensures that the external electrodes can move readily because they are not fixed by the gap preservation member, thus facilitating the relief of thermal stresses.
The batch connection of the connection portions and the electrodes during this connection step is also preferable from the viewpoint of mass production. Note that the problem of flection of the flexible substrate is most likely to occur during the batch connection, but since the connection is performed in a state in which the flexible substrate is held by the gap preservation member, this makes it possible to prevent the problem of flection of the flexible substrate.
In addition, the method could further comprise a step of forming a stress absorption layer between the semiconductor chip and the flexible substrate.
This stress absorption layer absorbs thermal stresses caused by the difference in coefficients of thermal expansion between the semiconductor chip and the flexible substrate, and also thermal stresses caused by the difference in coefficients of thermal expansion between the semiconductor chip and an external connection substrate (a mounting substrate). In addition, if the stress absorption layer is formed in the state in which the gap preservation member is interposed, the stress absorption layer can be formed in a state in which the gap is reliably held, and thus the stress absorption layer can be formed easily and also reliably.
Stress relief is particularly effective if the stress absorption layer is provided in at least a region corresponding to the external electrode formation portion.
The gap preservation member could be provided by printing a resin. For example, this gap preservation member could be formed by using a screen-printing method to print a solder resist. If a printing method is used, an existing printing device could be adapted therefor, which is advantageous because it makes it possible to reduce the costs of fabrication.
Alternatively, the gap preservation member could be provided by the ejection of a resin by an ink
Ho Hoai
Hoang Quoc
Oliff & Berridg,e PLC
Seiko Epson Corporation
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