Metal fusion bonding – Process – Plural joints
Reexamination Certificate
1999-11-16
2001-05-01
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S179100, C228S039000, C029S840000, C361S803000
Reexamination Certificate
active
06223973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to printed circuit boards, and more particularly to approaches for connecting one printed circuit board to another.
2. Disclosure Information
Printed circuit boards (PCBs) are available in a variety of different types. Some PCBs are rigid, such as those having a substrate made of alumina or FR-4 glass/epoxy laminate, while others are relatively flexible (i.e., “flex circuits”), such as those having a substrate made of polyimide, polyester, and the like. Sometimes it is necessary to connect one PCB to another; that is, to electrically connect the circuit traces of a first PCB to corresponding circuit traces on second PCB. This board-to-board connection can be made either directly or indirectly. Indirect connection is the more common approach, which utilizes one or more connectors as an intermediary between the two boards. For example, as illustrated in
FIG. 1
, one board
10
might have a through-hole type connector
90
with male pins
92
thereon, while the other board
20
might have a surface mount type connector
94
with female receiving sockets
96
therein. The connectors
90
/
94
not only electrically connect the respective traces
14
/
24
together, but also acts as a mechanical strain relief against shear or flexure of one board with respect to the other. On the other hand, direct connection approaches do not rely on an intermediate connector, and are usually limited to cases where one or both of the boards is a flex circuit. (Directly connecting two rigid boards together without an intermediate connector is typically not practical, because the solder joints between the boards' adjoined traces cannot withstand much shear or flexure of one board with respect to the other.)
The typical direct connection approach for connecting a first (flex circuit) PCB to a second (flex or rigid) PCB involves the steps of (1) arranging the respective traces in correspondingly matching arrays at the edge of each board, (2) applying solder paste, conductive adhesive, or the like to the ends of the traces where connection is to occur, (3) overlapping the edges of the PCBs and placing the respective trace arrays in direct contact with one another, (4) applying pressure and heat through a mandrel or hot bar to the overlapped area so as to melt the solder paste, and (5) removing the heat and pressure so as to form solid solder joints connecting each trace of the first PCB with its counterpart trace on the other PCB. This is known as the “hot bar solder reflow” process. In order to effectively reflow the solder, the temperature of the hot bar or mandrel is typically maintained at about 280-300° C.
When the more expensive polyimide is used as the flex circuit substrate material, the hot bar process may be used, since the glass transition temperature of polyimide is typically about 350° C. However, when the less expensive polyester material is used as the substrate, hot bar processing cannot be used, since the glass transition temperature of polyester is about 70° C. In fact, use of the hot bar process would melt, distort, and severely damage a flex circuit having a substrate made of polyester. Thus, hot bar and other direct connection processes typically cannot be used with polyester flex substrates, thus requiring the use of connectors and an indirect connection approach. This presents a dilemma, because although polyester is more attractive than polyimide from a materials cost standpoint, the cost of the connectors and associated processing often offsets much of the savings that polyester seems to provide in the first place. It would be desirable, therefore, to provide an alternative to hot bar processing which permits direct, connectorless connection between one or more flex circuits made of polyester substrate.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior art approaches by providing an apparatus and method for connecting together first and second PCBs, wherein the first PCB has a first plurality of circuit traces arranged on a first surface thereof and terminating proximate a first edge thereof, and wherein the second PCB has a second plurality of circuit traces corresponding to the first plurality of circuit traces and arranged on a second surface thereof. The method includes the steps of: (a) arranging the first and second PCBs with the first edge of the first PCB overlapping the second PCB, such that the first and second pluralities of circuit traces are matchingly facing each other and are separated from one another by a predetermined spacing K; (b) shielding the first and second PCBs with a non-solder-wettable shield having an aperture therethrough, such that substantially only the first edge and portions of the first and second PCBs immediately adjacent the first edge are exposed through the aperture; (c) introducing molten solder through the aperture proximate the first edge of the first PCB, so as to urge capillation of the molten solder between the first and second boards; and (d) allowing the molten solder to cool so as to form a plurality of solid solder joints each connecting a respective one of the first plurality of circuit traces with a corresponding one of the second plurality of circuit traces.
It is an object and advantage that the method and apparatus of the present invention may be used to solder together two or more PCBs, wherein at least one of the PCBs is a flex circuit.
Another advantage is that the method and apparatus of the present invention may be used successfully with PCBs having substrates made of lower melting point materials, such as polyester, without damaging the substrate the way hot bar soldering and other prior art approaches can.
These and other advantages, features and objects of the invention will become apparent from the drawings, detailed description and claims which follow.
REFERENCES:
patent: 4491562 (1985-01-01), Soga et al.
patent: 4526313 (1985-07-01), Hug et al.
patent: 4589584 (1986-05-01), Christiansen et al.
patent: 4708281 (1987-11-01), Nelson et al.
patent: 4717064 (1988-01-01), Popielarski et al.
patent: 4834660 (1989-05-01), Cotti
patent: 4897918 (1990-02-01), Osaka et al.
patent: 4981248 (1991-01-01), Hall
patent: 5128506 (1992-07-01), Dahne et al.
patent: 5227589 (1993-07-01), Weeks
patent: 5364011 (1994-11-01), Baker et al.
patent: 5418691 (1995-05-01), Tokura
patent: 5479320 (1995-12-01), Estes et al.
patent: 5533904 (1996-07-01), Nobel et al.
patent: 5604333 (1997-02-01), Kennish et al.
patent: 5609490 (1997-03-01), Beesch et al.
patent: 5617990 (1997-04-01), Thompson, Sr.
patent: 5644475 (1997-07-01), Woychik et al.
patent: 5679155 (1997-10-01), Velie
patent: 5704535 (1998-01-01), Thompson, Sr.
patent: 5727727 (1998-03-01), Ead
patent: 5777855 (1998-07-01), Yokajty
patent: 5820013 (1998-10-01), Ortiz
patent: 5825633 (1998-10-01), Bujalski et al.
patent: 5982626 (1999-11-01), Kodama
patent: 6071597 (2000-06-01), Yang et al.
Kiang Billy
Wong Stephen H. P.
Edmondson L.
Kajander John R.
Ryan Patrick
Visteon Global Technologies Inc.
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