INTERGRATED CIRCUIT LEAD FRAME

Abstract: An integrated circuit lead frame (10) for use in the plastic encapsulation of integrated circuit impedes the progress of contaminants to the bonding pads of an integrated circuit die by forming grooves (26) in the leads (18) interior the plastic package, providing an enlarged perforation (22) in the leads (18), and either extending the bonding area (24a, 24b) of the leads away from the perforation (22) of providing the bonding area directly behind the perforation (22).

Description: - 1- INTEGRATED CIRCUIT LEAD FRAME Technical Field This invention relates generally to lead frames and more particularly to lead frames for use in plastic encapsulation of integrated circuits. Background Art Although there are substantial cost savings for the plastic encapsulation of integrated circuits over ceramic encapsulation, ceramic packages have an advantage of providing a hermetic seal. With plastic packages, fluid-borne contaminants, such as chlorine, can infiltrate the plastic package along the plastic-lead interface to the wire bonding post. The contaminants then migrate along the surface of the bond wire to the bonding pad of the integrated circuit. The resulting corrosion of the aluminum bonding pad eventually causes an open circuit. One attempt to solve this long standing problem with plastic packages required that the integrated circuit be covered with a water resistant coating prior to encapsulation, thus requiring an additional step in the packaging process. Summary of the Invention An object of the present invention is to provide a lead frame for- use in plastic encapsulation of an integrated circuit which provides improved resistance against infiltration of contaminants into the integrated circuit. In carrying out the above and other objects and advantages of the present invention there is provided an integrated circuit lead frame having a major axis and a minor axis, a die mounting portion positioned generally symmetrically relative to said major and minor axes, and a first plurality of leads extending substantially parallel to said minor axis from a proximal end adjacent one side of said mounting portion and generally coplanar therewith to at least an encapsulation line intermediate the ends of said leads, characterized in that each of said leads includes a perforation extending orthogonal to said major and minor axes through said proximal ends, and that the portion of each of said leads between said proximal ends and said encapsulation line has a top surface and a bottom surface with at least one groove formed therein generally parallel to the major axis and generally between the perforation and the encapsulation line. Brief Description of the Drawings FIG. 1 is an illustration of an integrated circuit lead frame according to an embodiment of the present invention. FIG. 2 is a cross section of one of the leads used in the embodiment of FIG. 1. FIG. 3 is an illustration of an integrated circuit lead frame according to a second embodiment of the present invention. Detailed Description of the Drawings Shown in FIG. 1 is an integrated circuit lead frame 10 of the present invention comprised generally of an integrated circuit die mounting flag 12 positioned generally symmetrically relative to the major and minor axes 14 and 16, respectively, of the lead frame 10, and a plurality of leads 18, each of which extends, at least in part, parallel to minor axis 16 from a proximal end adjacent a respective side of the flag 12 and generally coplanar therewith to at least an encapsulation line 20. In use, an integrated circuit die (not shown) is attached to the flag 12 and the bonding pads thereof connected by fine wires to respective bonding portions formed on the OMPI proximal ends of the leads 18. In some circumstances, it may be desirable to displace the flag 12 somewhat below the plane of the leads 18 to facilitate the wire bonding operation. The die and the portions of the leads 18 within the encapsulation line 20 are then encapsulated in a suitable plastic compound. In the preferred form, each of the leads 18 has a perforation 22 extending orthogonal to the major and minor axes 14 and 16 respectively, through the portion thereof near the encapsulation line, to allow the encapsulation plastic to more securely anchor the lead 18 in place. It has been discovered, however, that a significant reduction in the likelihood of infiltration of fluid-borne contaminants may be obtained if the dimension of the perforation.22 parallel to the major axis 1 is selected to minimize the surface area of the lead 18 along which infiltration of such contaminants can progress from the encapsulation line 20 to the wire bonding site, without jeopardizing the strength of the respective lead 18. In additioπ r it has been discovered that the shortest of the leads 18 are most susceptible to contaminant damage. Accordingly, the proximal ends of leads 18a and 18b have respective bonding posts 24a and 24b extending substantially parallel to the major axis 14 from one edge of the respective leads 18a and 18b a substantial lateral distance therefrom to further retard infiltration by increasing the distance between the point of ingress of contaminants at the encapsulation line 20 and the wire bonding sites at the ends of the bonding posts 24a and 24b. Although the combination of the perforations 22 and the bonding posts 24a and 24b provides a significantly improved resistance to contamination damage, the preferred embodiment is greatly improved by providing a plurality of grooves on the upper and lower surfaces of each of the leads 18 generally parallel to the major axis 14 between the perforations 22 and the' encapsulation line 20. For Z example, in the cross section of the lead 18a shown in FIG. 2, three grooves 26 are provided on the top surface and two grooves on the bottom surface of the leads 18, with each groove being formed at an angle A of 90° at a depth B and C of .0012 +_ .0002 inches. Lead 18a has a thickness D of .0100 + .0004 inches. Shown in FIG. 3 is an integrated circuit lead frame 28 comprised generally of a flag 30 and a plurality of leads 32 configured similar to lead frame 10 of FIG. 1 with grooves 34 and perforations 36. Using a single lead 32a as an example, lead 32a has a bonding portion 38 at an end proximal flag 30 substantially along longitudinal axis 40 of lead 32a. In use an integrated circuit die is bonded to flag 30 and electrically connected via fine wire to leads 32 at, in the case of example lead 62a, bonding portion 38. Having bonding portion 38 directly behind a perforation 36 effectively interposes perforation 36 as a physical impediment in the path of contaminants . While the invention has been described in two embodiments, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.

Claims: CLAIMS 1. An integrated circuit lead frame having a major axis and a minor axis, a die mounting portion positioned generally symmetrically relative to said major and minor axes, and a first plurality of leads extending substantially parallel to said minor axis from a proximal end adjacent one side of said mounting portion and generally coplanar therewith to at least an encapsulation line intermediate the ends of said leads characterized in that each of said proximal ends includes a bonding post extending substantially parallel to said major axis from one edge of said lead a substantial lateral distance therefrom and that the portion of each of said leads between said proximal end and said encapsulation line has a top surface and a bottom surface with at least one groove formed therein generally parallel to the major axis and between the bonding post and the encapsulation line. 2. The integrated circuit lead frame of claim 1 further characterized in that each of said proximal ends includes a perforation extending orthogonal to said major and minor axes through said proximal end. 3. An integrated circuit lead frame having a major axis and a minor axis, a die mounting portion positioned generally symmetrically relative to said major and minor axes, and a first plurality of leads extending substantially parallel to said minor axis from a proximal end adjacent one side of said mounting portion and generally coplanar therewith to at least an encapsulation line intermediate the ends of said leads characterized in that each of said proximal ends includes a perforation extending orthogonal to said major and minor axes through said proximal end, and that the portion of each of said OMPI leads between said proximal end and said encapsulation line has a top surface and a bottom surface with at least one groove formed therein generally parallel to the major axis and generally between the perforation and the encapsulation line. 4. The integrated circuit lead frame of claim 3 further characterized iri that each of said leads has a bonding area between the perforation and the proximal end near the axis of the lead. 5. The integrated circuit lead frame of claim 3 further characterized in that each of said proximal ends includes a bonding post extending substantially parallel to said major axis from one edge of said lead a substantial lateral distance therefrom. OMPI

Inventors: BOND RICHARD J, BOND, RICHARD, J.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1983
Main classification: H01L23
IPC codes: H01L23