Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2001-03-20
2004-08-03
Talbot, Brian K. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S010000, C427S240000, C427S256000, C427S096400, C228S180220
Reexamination Certificate
active
06770319
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin coating method and apparatus for applying resin to a predetermined region of a printed wiring board.
2. Description of Related Art
Conventionally, the production of semiconductor devices, in which semiconductor elements are mounted on a printed wiring board, involves the insertion of an insulating resin between the printed wiring board pad and the semiconductor bump and, further, the use of insulating resin in regions of the printed wiring board that include leads. This so-called underfill is intended to protect the circuit surface and to strengthen the bond between the semiconductor and the printed wiring board.
Generally, there are two main methods of applying the insulating resin (hereinafter simply resin): Injecting the resin between the printed wiring board and the semiconductor elements after the semiconductor elements have been mounted on the printed wiring board, and mounting the semiconductor elements on a printed wiring board that has already been coated with resin.
Of the two methods of application, the latter is further divided into exposure and stamp methods.
The exposure method involves spraying drops of resin from a nozzle that is moved over the surface of the printed wiring board, covering a predetermined region with a coating having a thickness, for example, of approximately 50-100 &mgr;m.
By contrast, the stamp method involves dropping a predetermined amount of resin from a nozzle onto a central portion of the printed wiring board and then using the force with which the semiconductor elements are mounted on the printed wiring board to spread the resin over a predetermined region with a coating having a thickness, for example, of approximately 10-100 &mgr;m.
The stamp method of application has come to be used with less frequency for large semiconductor elements with surface dimensions on the order of millimeters, being optimally suited to smaller semiconductor elements having surface dimensions of 0.3 mm or less.
An example of the mounting of such smaller semiconductor elements on a printed wiring board is shown in
FIG. 1
, which shows a head slider assembly for a hard disk drive. In this case, a head IC chip
1
is mounted on a printed wiring board suspension
2
.
In such a case, the resin application device is usually a dispenser (not shown in the diagram) having a syringe filled with resin, the dispenser being able to raise and lower the syringe.
In order to apply the resin, a nozzle on a lower part of the syringe is positioned at a predetermined height above a surface of the suspension
2
and a predetermined amount of resin
3
is extruded from the syringe by compressed air. The extruded resin
3
is substantially spherical in shape, and contacts and adheres to the suspension
2
. When the syringe is lifted the resin
3
separates from the syringe and spreads across a predetermined position on the surface of the suspension
2
. Thereafter a head IC chip
1
is positioned above and pressed onto the suspension, thus further spreading the resin
3
as well as adhering and fixedly mounting the head IC chip
1
onto the suspension
2
.
More specifically, as can be seen in
FIG. 1
, a wiring pattern
4
may be formed on a top surface of the suspension
2
and a gold pad
5
may be formed at an edge portion of the wiring pattern
5
. At the same time, a gold bump
6
may be formed on a bottom surface of the head IC chip
1
. The gold pad
5
and the gold bump
6
are coupled and a predetermined region between the head IC chip
1
and the suspension
2
including the gold pad
5
and the gold bump
6
is covered with the resin
3
.
A plurality of suspensions
2
may for example be set atop a stage at a resin application device and the suspensions
2
subjected to the above-described coating process. In this case, in order to resin-coat a predetermined product lot with a predetermined amount of resin, the resin application device is set to specific conditions at the start of coating. When after repeated coating the resin is used up, a new syringe is installed.
In the above-described case, the head IC chip
1
is, for example, just 1×1 mm, and so the amount of resin used in the coating is, for example, approximately 0.05 mg. Such small amounts over such small surfaces requires precision in the application of the resin
3
.
However, because the amount of resin
3
involved in individual applications is small, it can happen that slight changes in ambient conditions during application, such as, for example, slight changes in temperature, causes slight changes in the amount of resin
3
applied, despite the resin application device being set to predetermined conditions beforehand.
Conventionally, in order to maintain the amount of resin
3
to be applied at the predetermined volume, a visual inspection is made of the amount of resin, if any, protruding from the edges of the semiconductor elements in a state in which the printed wiring board has been coated and the semiconductor elements mounted thereon in order to determine if too much resin or too little resin is being applied, after which the resin amount is adjusted as necessary. Additionally, visual inspection of the resin drop just before it separates from the nozzle or the external appearance of the resin
3
coating the stage are also used to determine the presence of change in the amount of resin applied.
However, the very small amounts of resin involved make it difficult to discern changes in that amount by the conventional methods. In addition, adjustment of the amount is often left to the discretion of an operator, which means it is often done manually and at arbitrary times. Such methods of adjustment are unsuited to cases in which the amount of resin applied changes continuously due to a variety of environmental and other factors.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved and useful resin coating method and apparatus in which the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by a resin coating method for applying resin to a predetermined region of a printed wiring board comprising the steps of:
imaging an external appearance of the resin extruded from a resin application device; and
automatically adjusting an amount of the resin extruded from the resin application device based on the external appearance of the resin obtained in the imaging step.
The above-described object of the present invention is also achieved by a resin coating apparatus for applying resin to a predetermined region of a printed wiring board, comprising:
an imaging unit for imaging an external appearance of the resin extruded from the resin coating apparatus; and
an automatic adjustment unit for automatically adjusting an amount of the resin extruded from the resin coating apparatus based on the external appearance of the resin obtained in the imaging step.
According to the above-described aspects of the present invention, the amount of resin expelled, in other words, the amount of resin to be used to coat the printed wiring board, is set according to the dimensions of the semiconductor elements mounted on the printed wiring board. The present invention is most effective with semiconductor elements measuring not more than 0.3 mm a side, though it is not limited to use with semiconductor elements of such dimensions.
A preferred method for automatically adjusting the amount of resin extruded from the resin coating apparatus is one in which a difference between a preset coating amount and an actual coating amount as determined by the external appearance of the resin is sensed and this difference used as feedback to adjust the amount of resin extruded. In this case, it is preferable that relational data relating the external appearance of the resin and the coating amount be stored as a reference table in the resin coating apparatus. An ordinary camera can suffice for use as the imaging device. As a method of adjus
Baba Shunji
Kainuma Norio
Kira Hidehiko
Kobae Kenji
Kobayashi Hiroshi
Fujitsu Limited
Staas & Halsey , LLP
Talbot Brian K.
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