Drying and gas or vapor contact with solids – Apparatus – Sheet – web – or strand
Reexamination Certificate
1998-11-04
2001-11-13
Kwon, John (Department: 3747)
Drying and gas or vapor contact with solids
Apparatus
Sheet, web, or strand
C034S236000, C034S617000, C034S620000
Reexamination Certificate
active
06314660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to systems and methods for manufacturing tab head assembly (THA) flex circuits. More specifically, the present invention relates to drive systems for linear bake ovens used in the fabrication of flex circuits.
2. Description of the Related Art
Flexible circuits, often referred to as ‘flex circuits’, are used in a number of applications. In an illustrative application, a flex circuit is used to convey electrical signals from a printer to an inkjet pen. The flex circuit used for this application is often fabricated on tab head assembly (THA) tape. THA tape is a strip of polyester or polyimid material such as a Mylar or Kapton which provides a substrate into which multiple copper conductors are embedded. The tape is typically on the order of 2 inches wide and 2 mils (0.002 inches) thick. A plurality of sprocket holes are provided along the edge of the tape on either side of a central die area onto which a silicon die is bonded with a suitable epoxy.
Electrical signals are communicated from the printer to the die through the copper circuitry in the Kapton material and into the silicon die. As described more fully in U.S. Pat. No. 5,568,171 issued Oct. 22, 1996 to Keefe et al., the specification and drawings of which are incorporated herein by reference, the electrical signals selectively activate a number of resistors in integrated circuit print heads fabricated in the die. The flow of current through the resistors heats and vaporizes ink and cause it to be expelled through a small nozzle toward print media, e.g., paper.
Fabrication of the THA involves pulling the tape off a reel with a linear drive system such as that manufactured and sold by Owens Design in Fremont, Calif. The drive system pulls the tape through a bake oven which cures the epoxy interface between the Kapton and the die. The conventional oven is actually eight ovens arranged in series to provide varying temperature environments for the tape as it moves therethrough: a gradually increasing thermal environment in a first few ovens, a stable temperature environment through the middle ovens, and a decreasing temperature environment through the last two or three ovens.
Current manufacturing techniques require a high tension (e.g. on the order of 1200 grams) on the tape throughout the curing process. The conventional linear drive system maintains high tension with supply and take-up sprocket wheels having a plurality of sprockets designed to engage sprocket holes on the THA tape. The high tension is maintained with a 90° bend of the tape around the sprocket wheels.
Unfortunately, for current more demanding applications, the desired length of the rigid silicon die has grown to one inch. Accordingly THA tape carrying such dies can not be wrapped around a sprocket wheel under such high tension without an unacceptable amount of stress, deformation, and damage to the tape. Such damage to the THA tape has been found to include excessive wrinkling, delamination, broken TAB contacts, or sprocket hole damage.
Hence, there is a need in the art for a safe and effective system and method for fabricating THA tape for inkjet pens without exposing the tape and any long die thereon to undesirable stress, deformation, and damage.
SUMMARY OF THE INVENTION
The need in the art is addressed by the system and method for fabrication of flexible circuits of the present invention. The inventive system includes an oven and three or more independent tensioners for moving a strip of THA flex tape therethrough. In total, N tensioners are provided. The tensioners provide a cumulative tension force T on the tape and each tensioner applies T/N of the total tension. The tension is applied tangentially in a single plane of the tape along a direction parallel to the longitudinal axis thereof
In the illustrative embodiment, the tensioners are sprocket wheels. Eight sprocket wheels are disposed on a supply side of the system and eight are disposed on a take-up side of the system. The sprocket wheels are adapted to engage sprocket holes in the tape. The cumulative tension is applied over a segment of the tape of a length.
The tape is THA tape typically made of polyimid or other suitable material. The tape has a sprocket hole area and a die area. A silicon die is typically bonded to the die area with a suitable epoxy. Copper conductors embedded in the tape communicate electrical signals from a printer or other mechanism to the silicon die.
The inventive system maintains high tension on the tape as it moves through a plurality of bake ovens. High tension is distributed over a longer area of the tape than with prior systems and is maintained without exposing the flex circuit to a stressful bend angle. In addition, each sprocket hole experiences minimal force due to the force/tension distribution methodology of the present invention.
REFERENCES:
patent: 2302730 (1942-11-01), Woodford
patent: 2800726 (1957-07-01), Koch et al.
patent: 3418724 (1968-12-01), Futer
patent: 3745670 (1973-07-01), Hartwig
patent: 4194300 (1980-03-01), Swanson et al.
patent: 4949474 (1990-08-01), Berg
patent: 4991315 (1991-02-01), Fakck
patent: 5537757 (1996-07-01), Gray
patent: 5568171 (1996-10-01), Keefe et al.
patent: 497769 (1930-05-01), None
patent: 793216 (1958-04-01), None
patent: 606530 (1960-07-01), None
Dangelewicz John
Steinfield Steven W.
Hewlett--Packard Company
Kwon John
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