Special receptacle or package – Holder for a removable electrical component – Bar or tapelike carrier for plural components
Reexamination Certificate
1999-08-03
2001-03-27
Sewell, Paul T. (Department: 3728)
Special receptacle or package
Holder for a removable electrical component
Bar or tapelike carrier for plural components
C206S389000
Reexamination Certificate
active
06206198
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor devices and more specifically to packing reels used to hold packaged semiconductor devices for storage and baking.
BACKGROUND OF THE INVENTION
Surface mount integrated circuit devices are subject to delamination of the encapsulating plastic mold compound from the lead frame during solder attachment to a printed wiring board. In extreme cases the package cracks, which may in turn result in opens, or other reliability failures during use, or in testing. The failure mechanism has been traced to absorption of moisture by the molding compound, which vaporizes when the device is subjected to rapid heating during solder reflow processing, and the resulting vapor exerts pressure at the plastic to metal interface. This problem has intensified as packages have become larger and thinner.
In order to avoid the failure, plastic encapsulated devices which are subject to the problem must be baked relatively slowly at a temperature high enough, and for sufficient length of time to drive the moisture out of the package. Once the devices have been dried, they are sealed in a vapor barrier container, along with a desiccant for shipping and storing. The devices undergo dry baking after they have completed assembly processing and testing, and again after the containers have been opened, if they have not been used within the allowable time. Standards committees, such as EIA (Electronic Industries Association) and JEDEC (Joint Electronic Devices Engineering Council) have set specific standards related to this issue based on integrated circuit packages type, standards for testing procedures, and also standards for packing containers used for the shipping and storage.
The process of baking plastic encapsulated integrated circuits, and sealing in vapor barrier containers is generally known as dry packing. Historically, larger devices which require dry packing are placed in plastic trays with a cavity or recess sized to hold each device securely. Baking to remove absorbed water can be performed either in these trays, or the devices can be loaded into the trays immediately after dry baking. Trays loaded with dried components are placed in a seal-able vapor bag with a desiccant for shipping and storing. The trays are constructed of plastic materials which are thermally stable over the temperature range required for dry baking, typically 125 deg C. Packing trays have a number of drawbacks; namely, they are constructed of costly materials, they are bulky which contributes significantly to the shipping weight and volume, and they require space consuming automated pick and place equipment. In an attempt to minimize costs, some trays are returnable, thereby adding another expense. Automated pick and place equipment consists of large x/y tables with robot handling.
Small integrated circuit packages which require no dry packing are usually placed directly into a sprocket guided carrier tape which has a series of recesses sized to fit the devices. The recesses are set at a defined pitch, and the devices are held in place by a cover tape. The tape loaded with semiconductor devices is wound onto a packing reel, and the reel assemblage stored in a corrugated container. Tape and reel dimensions are specified by standards in order to insure uniformity between suppliers. Generally, the tape widths range from 8 mm to 56 mm and the reel is 330 millimeters in diameter. However, the reel diameter may be changed according to the volume of devices needed.
Tape and reel packaging provides a compact means for storing, transporting, and dispensing integrated circuits. The reel is placed directly onto a relatively small piece of equipment for picking and placing the circuits, and as a result this type of handling equipment has become much more desirable to the end user than the more bulky x/y table used to pick and place from trays.
Consequently, a need for packing reels and an assemblage which is compatible with dry baking integrated circuit devices has developed. Simply using existing reels constructed of high temperature plastic has not been successful because the design is inefficiency for baking, and because high temperature plastics are generally more dense, thus resulting in additional shipping weight.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a packing reel which conforms to existing industry standards, and is capable of being changed with respect to size and labeling, but which can be used to efficiently bake encapsulated integrated circuits for removing absorbed water. In order to meet this requirement, the reel must be dimensionally stable for extended periods of time at 125-130 deg C.
Packing reels of prior art are not optimized for air flow through the reel, thus adding to the time required to heat and cool the assemblage during baking in a forced air oven. It is an object of this invention to provide a reel with hub and flange structure which allows air to flow through the reel, thereby reducing the time required to heat up and cool down the components, and thus supporting a decreased processing cycle time.
Further, it is an object of this invention to provide a reel having a means for uniform heating of the devices by allowing good air flow through the reel. Uniformly heating will allow reliable baking of each component.
It is an object of this invention to provide a reel which can be baked at the dry bake temperature repeatedly, such as for initial drying, as well as for rebaking of either fully loaded or partially loaded reels.
It is also an object of this invention to conserve the amount of material used in construction of the reel, thereby eliminating unnecessary consumption of costly high temperature thermoplastic. The reel of this invention may be formed by low cost injection molding which further takes advantage of material conservation, and avoids waste disposal. Further, a relatively lightweight reel is provided which minimizes shipping weight.
It is also an object of this invention to provide a reel which can be constructed of either thermally stable plastic suitable for baking, or a plastic which is not suitable for baking, but does take advantage of the relatively lighter weight construction.
It is still further an object of the invention to provide an assemblage which includes a reel with carrier and cover tapes which meet the dry bake requirements.
It is still further an object of this invention to provide a tape and reel assemblage suitable for leaded surface mount packages, as well as more advanced devices such as ball grid array (BGA) or chip scale packages (CSP).
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings. The drawings constitute a part of this specification and include an exemplary embodiment of the invention, which may be embodied in various forms. It is to be understood that in some instances aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
REFERENCES:
patent: 5136827 (1992-08-01), Sawaya
patent: 5238105 (1993-08-01), Smiley
patent: 5318181 (1994-06-01), Stover et al.
patent: 5494168 (1996-02-01), Hart
patent: 5875897 (1999-03-01), Duncan et al.
Hayden Michael
Troxtell Clessie
Bui Luan K.
Honeycutt Gary C.
Sewell Paul T.
Telecky Fred
Texas Instruments Incorporated
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