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 for preparing an integrated circuit for connection to a surface, the integrated circuit including lead contacts and leadless contacts, is provided. The method includes providing the integrated circuit, applying a first solder paste to the leadless contacts, forming solder balls on the applied solder paste, heating the solder balls, thereby removing at least a portion of the first solder paste and bringing the solder balls into electrical contact with the leadless contacts, the base of the solder balls being generally aligned in a plane, and bending the lead contacts into gull wings, the base of the gull wings being substantially coplanar with the plane, wherein the base of the gull wings and the base of the at least one of the solder balls collectively generally define a contact plane.
The above embodiment may include various features. The method may include: determining, before the bending and after the heating, a lateral distance between the lead contacts and the base of at least one of the solder balls; and/or electrically connecting the lead contacts and leadless contacts to the surface. The electrically connecting may include applying a second solder paste to the surface, soldering the base of the gull wings to the surface, and heating the solder balls, thereby removing at least a portion of the second solder paste and bringing the solder balls into electrical contact with the surface, wherein the integrated circuit will be in electrical contact with the surface through both the leadless contacts and the lead contacts. The providing the integrated circuit may include providing an integrated circuit with the lead contacts attached to the body of the integrated circuit and extending laterally away from the body. The forming solder balls may include forming solder balls of about 10 mils in diameter and/or forming solder balls of substantially equal size.
According to another embodiment of the invention, a method for preparing an integrated circuit for connection to a surface, the integrated circuit including lead contacts and leadless contacts, is provided. The method includes providing the integrated circuit, applying a first solder paste to the leadless contacts, connecting bent leads to the applied solder paste, soldering the bent leads, thereby removing at least a portion of the first solder paste and bringing the bent leads into electrical contact with the leadless contacts, the base of the bent leads being generally aligned in a plane, and bending the lead contacts into gull wings, the base of the gull wings being substantially coplanar with the plane, wherein the base of the gull wings and the base of the at least one of the bent leads collectively generally define a contact plane.
The above embodiment may have various features. The method may include: determining, before the bending and after the soldering, a lateral distance between the lead contacts and the base of at least one of the bent leads; and/or electrically connecting the lead contacts and leadless contacts to the surface. The electrically connecting may include applying a second solder paste to the surface, soldering the base of the gull wings and the base of the bent leads to the surface, thereby removing at least a portion of the second solder paste and bringing the bent leads into electrical contact with the surface, wherein the integrated circuit will be in electrical contact with the surface through both the leadless contacts and the lead contacts. The providing the integrated circuit may include providing an integrated circuit with the lead contacts attached to the body of the integrated circuit and extending laterally away from the body. The bent leads may be either S-leads or C-leads. The connecting may include providing the bent leads on a fixture, and orientating the fixture to bring the bent leads into alignment with the leadless contacts; the bent leads made be removed from the fixture after the bent leads are connected to the integrated circuit.
According to yet another embodiment of the invention, a method for preparing an integrated circuit for connection to a surface, the integrated circuit including lead contacts and leadless contacts, is provided. The method includes providing the integrated circuit, applying a conductive epoxy to the leadless contacts, the base of the epoxy being generally aligned in a plane, and bending the lead contacts into gull wings, the base of the gull wings being substantially coplanar with the plane, wherein the base of the gull wings and the base of the at least one of the bent leads collectively generally define a contact plane.
The above embodiment may include various optional features. The method may include: determining, before the bending and after the applying, a lateral distance between the lead contacts and the base of at least one of the bent leads; and/or electrically connecting the lead contacts and leadless contacts to the surface. The electrically connecting may include applying a second solder paste to the surface, soldering the base of the gull wings to the surface, curing the conductive epoxy, wherein the integrated circuit will be in electrical contact with the surface through both the leadless contacts and the lead contacts. The providing the integrated circuit may include providing an integrated circuit with the lead contacts attached to the body of the integrated circuit and extending laterally away from the body.
According to still yet another embodiment of the invention, a method for preparing an integrated circuit for connection to a surface, the integrated circuit including lead contacts and leadless contacts, is provided. The method includes providing the integrated circuit, applying a first solder paste to the leadless contacts, placing preformed conductive metal pieces on the first solder paste, soldering the metal pieces, thereby removing at least a portion of the first solder paste and bringing the metal pieces into electrical contact with the leadless contacts, the base of the metal pieces being generally aligned in a plane, and bending the lead contacts into gull wings, the base of the gull wings being substantially coplanar with the plane, wherein the base of the gull wings and the base of the at least one of the metal pieces collectively generally define a contact plane.
The above embodiment may have various optional features. The method may include: determining, before the bending and after the soldering, a lateral distance between the lead contacts and the base of at least one of the metal pieces; and/or electrically connecting the lead contacts and leadless contacts to the surface. The electrically connecting may include applying a second solder paste to the surface, soldering the base of the gull wings and the metal pieces to the surface, wherein the integrated circuit will be in electrical contact with the surface through both the leadless contacts and the lead contacts. The providing the integrated circuit may include providing an integrated circuit with the lead contacts attached to the body of the integrated circuit and extending laterally away from the body.
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:
The instant application 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 | |
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61064337 | Feb 2008 | US |
Number | Date | Country | |
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Parent | 12379524 | Feb 2009 | US |
Child | 12929224 | US |