Patent Application
20110157855
1. Field of the Invention
The present invention relates to a connection methodology. More specifically, the present invention relates to methodologies for connecting hybrid chips to printed wiring boards where the chips contain both leads and leadless contacts.
2. Discussion of Background Information
An integrated circuit (“IC”) typically comes in two varieties. One variety includes ICs with metal leads extending therefrom that carry power, ground, input and output signal. The metal leads are often rigid and bent into a shape known as a “gull wing.” The other variety uses “leadless” contacts, in which conductive pads are integrated into the surface of the IC. Varieties of methods are known for connecting the leads, leaded ICs, or conductive pads of leadless ICs to printed circuit boards.
Recently a hybrid chip has been introduced that utilizes both gull wing leads and leadless contact pads on the bottom of the chip.
According to an embodiment of the invention, a method is provided for connecting an integrated circuit to a surface of a printed wiring board. The integrated circuit includes lead contacts and leadless contact pads. A first solder paste is applied to the leadless contact pads of the integrated circuit, and preformed conductive pieces are placed on the first solder paste. The preformed conductive pieces are slugs that have, for example, a cylindrical shape or a rectangular cross-section. The preformed conductive pieces are heated and brought into electrical contact with the leadless contact pads. The lead contacts are formed into gull wings. The bases of the preformed conductive pieces are generally aligned in a plane, and the bases of the gull wings are substantially coplanar with the plane such that they collectively generally define a contact plane. A second solder paste is applied on the surface, and the bases of the gull wings and the preformed conductive pieces are soldered to the second solder paste on the surface so that the integrated circuit is in electrical contact with the surface through both the leadless contact pads and the lead contacts. The preformed conductive pieces comprise a conductive material (e.g., a copper alloy) that has a higher melting point than the first solder paste and the second solder paste such that the preformed conductive pieces do not melt during heating or soldering that is described above.
In accordance with another embodiment, an apparatus is provided that comprises a printed wiring board having a surface, a plurality of preformed conductive pieces, an integrated circuit comprising a body and leadless contact pads, and a plurality of lead contacts. The lead contacts are formed into gull wings, and attached to the body of the integrated circuit such that they extend laterally away from the body. The preformed conductive pieces comprise a conductive material having a higher melting point than solder paste, and electrically couple the leadless contact pads to the surface of the printed wiring board. The bases of the preformed conductive pieces are generally aligned in a plane, and the base of each of the gull wings is substantially coplanar with the plane. The bases of the gull wings and the bases of the preformed conductive pieces are soldered to the surface of the printed wiring board so that the integrated circuit is in electrical contact with the surface through both the leadless contact pads and the lead contacts. Because the conductive material of the preformed conductive pieces has a higher melting point than solder paste, the preformed conductive pieces do not melt when soldered onto the surface of the printed wiring board and more reliable electrical and mechanical contact can be made between the preformed conductive pieces and the surface of the printed wiring board.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.
The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of certain embodiments of the present invention, in which like numerals represent like elements throughout the several views of the drawings, as follows.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
Referring now to
Solder paste 208 (thickness exaggerated for illustration) is applied to conductive contact pads 206 at step 304. At step 306, solder balls 210 are then applied on top of solder paste 208. The solder balls 210 are then heated to bond with conductive pads 206 at step 308; this tends to remove solder paste 208, such that it is no longer shown in
Each solder ball 210 is preferably about 10 mils in diameter when deposited, although they are expected to expand as solder flows during soldering. Each solder ball 210 is preferably made from a material with a melting point of 290 degrees or above. Pure copper or a 10/90 alloy of tin and lead are suitable for this environment.
The lower surface of the solder balls 210 will roughly define a base plane 212 at which the solder balls 210 will later connect to a printed wiring board. At step 310 the distance between that plane and leads 204 is then determined, and at step 312 the leads 204 are bent into a second orientation that includes gull wings 214. The lateral wing portions 216 of gull wings 214 lie in the base plane 212, thus forming a collective contact plane.
At step 314, solder paste 218 is applied using a stencil at the appropriate locations on a printed wiring board 220. At step 316, wings 214 are then soldered onto their respective portions of solder paste 218, while the solder balls 210 are heated to form connections onto the printed circuit board 220. The connections at step 316 can be simultaneously or in any order.
Solder balls 210 tend to have minimal compliancy and tend to crack under stress. The connections of
Each bent lead is preferable 0.40 mils high, and made from a copper alloy. In the alternative, small form factor bent leads of the type shown in co-pending U.S. patent application Ser. No. 11/979,487 (filed on Nov. 7, 2007, the disclosure of which is herein incorporated by reference in its entirety) can be used.
The lower portion of the connected bent leads will roughly define a base plane 412 at which the bent leads 410 will later contact the printed wiring board. At step 510 the distance between that plane and leads 404 is then determined, and at step 512 the leads 404 are bent into a second orientation that includes gull wings 414. The wing portions 416 of gull wings 414 lie in the base plane 412, thus forming a collective contact plane.
At step 514, solder paste 418 is applied using a stencil at the appropriate locations on a printed wiring board 420. At step 516, wings 414 and leads 410 are then soldered onto their respective portions of solder paste 218. The connections at step 516 can be made simultaneously or in any order.
Bent leads have a compliancy that allows them to shift during thermal stress. This makes the connection of
At step 714, solder paste 618 is applied using a stencil at the appropriate locations on a printed wiring board 420 that correspond to the contact points for wing portions 616. At step 716, wings 614 are soldered onto their respective portions of solder paste 618. At step 718, the epoxy is cured. The connections at steps 716 and 718 can be made simultaneously or in any order.
Conductive epoxy is more compliant than solder but less compliant than bent leads. It is thus suitable for use in environments with moderate to high thermal expansion and/or cycles of thermal expansions, although not to the same extent as bent leads. Thus, for example, this connection methodology is not preferable for avionics applications.
Referring now to
Each slug 810 is preferably about 5 mils in height, although other heights could be used.
The lower portion of the slugs 810 will roughly define a base plane 812 at which the slugs 810 will contact the printed wiring board. At step 910 the distance between that plane and leads 804 is then determined, and at step 912 the leads 804 are bent into a second orientation that includes gull wings 814. The wing portions 816 of gull wings 814 lie in the base plane 812, thus forming a collective contact plane.
At step 914, solder paste 818 is applied using a stencil at the appropriate locations on a printed wiring board 820. At step 916, wings 814 are then soldered onto their respective portions of solder paste 818, while the slugs 810 are heated to form connections onto the printed circuit board 820. The connections at step 916 can be made simultaneously or in any order.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to certain embodiments, it is understood that the words that have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of any current or future claims.
Various claims below recite terms for which the following additional discussion may be relevant. For example:
This does not require nor exclude that the lead may be made of Pb or include Pb.
This application is a divisional of U.S. Utility application Ser. No. 12/379,524 which claims priority to U.S. Provisional Application 61/064,337 filed on Feb. 28, 2008, the disclosure of which is expressly incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61064337 | Feb 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12379524 | Feb 2009 | US |
| Child | 13042903 | US |
