Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor
Reexamination Certificate
1998-07-10
2001-02-13
Saadat, Mahshid (Department: 2815)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
C438S127000, C438S612000, C438S613000, C438S614000
Reexamination Certificate
active
06187610
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention is concerned with an electronic package and particularly concerned with a thin, ball grid array flexible panel, and method for its fabrication. More particularly, the present invention is concerned with a TBGA flexible panel that includes a solder mask and overcomes problem of distorting the flexible film carrier.
2. Background Art
Electronic packages that include a thin film circuit member as an integral part thereof are known in the industry, with examples being defined in U.S. Pat. No. 4,849,856 to Funari et al., and U.S. Pat. No. 4,914,551 to Anschel et al., both of which are assigned to the same assignee as the present invention. In these electronic package structures, solder bonds are commonly used. In one technique, an electronic device or module (semiconductor chip) is mounted onto a packaging thin film structure in a “flip-chip” orientation. In this orientation, the surface of the chip having contact locations is placed facing the thin films circuit member. The contact locations on the chip and the respective thin film conductive elements are electrically connected using solder structures, also referred to as controlled collapse chip connections (C4's). Polyimides are frequently used as the flexible thin film structure with metal layers being vacuumed deposited, laminated, or glued thereon.
Employing a C-4 type connection to attach a semi-conductor device to an organic flexible substrate presents fabrication problems. In particular, because of the flexible nature of the organic substrates, they tend to warp or bend during processing and temperature fluctuations. In addition, in an effort to significantly reduce the cost of individual modules on a carrier, it has been suggested to subject all of the solder balls to reflow on mass rather than individual solder ball connections. Because solderable materials exist extremely close to each pad, a solder mask must be employed to maintain the solder at each pad. Although using a solder mask overcomes this problem, it has created another problem. In particular, placing the solder mask on the flexible film carrier causes the flexible flimsy film carrier panel to badly distort. However, it is necessary that the flexible film carrier be reasonably flat or planar to properly carry out the mask reflow technique. Accordingly, it would be desirable to be able to employ a solder mask without the concomitant problem of distorting the flexible film carrier associated with using the solder mask.
SUMMARY OF INVENTION
The present invention makes it possible to use a mask reflow technique employing a solder mask, while at the same time significantly reducing, if not entirely eliminating the problem of distortion.
More particularly, the present invention is concerned with an electronic package that comprises a flexible film carrier having electronic circuitry on both of its major surfaces and a plurality of solder interconnection pads on a first major surface. The electronic package further includes a plurality of modules located on the first major surface of the flexible film carrier and are attached to the carrier by solder balls interconnected to the solder interconnection pads. The solder mask layer is located on both major surfaces of the flexible film carrier; provided that areas between subsequently to be applied individual modules on the first major surface are free from solder mask material.
The present invention is also related to a method for fabricating the above disclosed electronic package. The method includes providing a flexible film carrier having electronic circuitry on both major surfaces thereof and a plurality of solder interconnection pads on a first major surface thereof. A solder mask layer is provided on both major surfaces of the flexible film carrier, whereby there exist areas between subsequently to be applied adjacent individual modules on the first major surface that are free from the solder mask. Modules having solder balls are located on the film corner with the solder balls being mated to corresponding solder interconnection pads. The solder balls are then subjected to reflow in order to bond the chips to the flexible film carrier. The absence of solder mask material in areas between adjacent individual modules significantly reduce the stress thereby reducing the distortion. The areas free from the solder mask material act as hinges relative to the stiff, slightly distorted portions that are not relieved. In addition, the presence of the solder mask on the second major surface of the flexible film carrier helps to strengthen the solder joint.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other indifferent embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.
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Holzmann et al, “New Techniques Eliminate Solder Paste from Printed Circuit Assembly Operation”,Surface Mount International Conference&Exposition, Sep. 1-3, 1992, pp. 588-598.
Armezzani Gregg Joseph
Ives Robert Nicholas
Pierson Mark Vincent
Tull Terry Alan
Diaz José R.
Fraley, Esq. Lawrence R.
International Business Machines - Corporation
Ratner & Prestia
Saadat Mahshid
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