CA1145860A - Leadframe for leaded semiconductor chip carriers - Google Patents
Leadframe for leaded semiconductor chip carriersInfo
- Publication number
- CA1145860A CA1145860A CA000369692A CA369692A CA1145860A CA 1145860 A CA1145860 A CA 1145860A CA 000369692 A CA000369692 A CA 000369692A CA 369692 A CA369692 A CA 369692A CA 1145860 A CA1145860 A CA 1145860A
- Authority
- CA
- Canada
- Prior art keywords
- leads
- leadframe
- chip
- support
- lead
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/48—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor
- H01L23/488—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor consisting of soldered or bonded constructions
- H01L23/495—Lead-frames or other flat leads
- H01L23/49541—Geometry of the lead-frame
- H01L23/49565—Side rails of the lead frame, e.g. with perforations, sprocket holes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/481—Disposition
- H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
- H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
- H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
- H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
- H01L2224/491—Disposition
- H01L2224/4912—Layout
- H01L2224/49171—Fan-out arrangements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
- H01L2224/732—Location after the connecting process
- H01L2224/73251—Location after the connecting process on different surfaces
- H01L2224/73265—Layer and wire connectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
- H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L24/42—Wire connectors; Manufacturing methods related thereto
- H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L24/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
- H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L24/42—Wire connectors; Manufacturing methods related thereto
- H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L24/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/01—Chemical elements
- H01L2924/01019—Potassium [K]
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/095—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00 with a principal constituent of the material being a combination of two or more materials provided in the groups H01L2924/013 - H01L2924/0715
- H01L2924/097—Glass-ceramics, e.g. devitrified glass
- H01L2924/09701—Low temperature co-fired ceramic [LTCC]
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
- H01L2924/161—Cap
- H01L2924/1615—Shape
- H01L2924/16152—Cap comprising a cavity for hosting the device, e.g. U-shaped cap
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Lead Frames For Integrated Circuits (AREA)
Abstract
A LEADFRAME FOR LEADED SEMICONDUCTOR CHIP CARRIERS
Abstract of the Disclosure A leadframe with parallel side members and parallel transverse members defining chip receiving areas along the frame, has a chip pad at each area. A support lead extends from each corner of the chip pad to corresponding conjunctions of side and transverse members. A
U-shaped support bar extends between each adjacent pair of support leads, each support bar including spaced parallel leg portions connected at inner ends to the support leads and at the outer ends by a lead support portion.
Leads extend from each lead support portion towards the chip pad. By this means the chip can be assembled to the pad and wire bonding between chip and leads carried out and the leads can be preformed or not, as desired, prior to encapsulation. After encapsulation, the lead support portions can be trimmed off but the encapsulated device is still held in the lead frame but the leads are electrically isolated from each other. Testing can be carried out while devices are still in the leadframe.
Abstract of the Disclosure A leadframe with parallel side members and parallel transverse members defining chip receiving areas along the frame, has a chip pad at each area. A support lead extends from each corner of the chip pad to corresponding conjunctions of side and transverse members. A
U-shaped support bar extends between each adjacent pair of support leads, each support bar including spaced parallel leg portions connected at inner ends to the support leads and at the outer ends by a lead support portion.
Leads extend from each lead support portion towards the chip pad. By this means the chip can be assembled to the pad and wire bonding between chip and leads carried out and the leads can be preformed or not, as desired, prior to encapsulation. After encapsulation, the lead support portions can be trimmed off but the encapsulated device is still held in the lead frame but the leads are electrically isolated from each other. Testing can be carried out while devices are still in the leadframe.
Description
This invention relates to a leadframe for leaded semiconductor chip carriers.
In the manufacture of semiconductor chips, the chips are mounted on a die pad, and connections made between contact areas on the chip and leads which will eventually be used to connect the final device into a circuit, as by insertion on a printed circuit board (PCB). The chip is packaged, in one of a variety of ways, for example hermetic and non-hermetic encapsulation.
With the extremely large numbers being produced and the need to reduce labour content and to maintain high standards of accuracy and minimal rejection rates, it is favourable to handle assembly in strip form, a leadframe having a number of chip positions, with leads extending from the frame towards a chip mounting position. One such form of leadframe is illustrated and described in U.S. patent no. 4,214,364, issued July 29, 1980~ in the name of the present assignees.
Several problems arise in leadframes, and their use.
Ideally they should be suitable for both hermetic and non-hermetic encapsulation. It would be convenient if the leadframes could be processed with the leads unformed, that is flat and in the same plane as the frame, or with the leads preformed, that is with leg portions bent down. Electroplating is usually carried out on the leg portions.
Protection of the chip from electrostatic discharge during processing is important. Precision forming and cropping is also important and becoming increasingly so with the continual reduction in lead width and closer spacing of leads. Eventually reel to reel automated processing is envisaged and the leadframe should be easily and cheaply manufactured.
The present invention provides a leadframe which provides :1~!L4S~60 for the above problems. A leadframe in accordance with the present invention has parallel, spaced apart, side members and parallel, spaced apart, transverse members. The transverse members extend between, and connect to, the side members, to define a plurality of areas spaced along the frame. A rectangular die or chip pad is positioned centrally in each area with its sides parallel to the side members and transverse members of the frame. A support lead extends from each corner of the die pad to the corresponding conjunction of side and transverse members. A U-shaped support bar extends between each adjacent pair of support leads, the bar including parallel spaced leg portions connected at inner ends to the support leads and connected at outer ends by a lead support portion, the lead support portions parallel to related side and transverse members. A
plurality of leads extend from each lead support portion inwards towards the die pad, with inner ends adjacent to but spaced from the die pad.
The invention will be readily understood by the following description of a particular embodiment, by way of example, in conjunction with the accompanying drawings, in which:-Figure 1 is a plan view of part of a strip of leadframes, with different process steps illustrated at different frames;
Figures 2, 3 and 4 are cross-sections on the lines II-II;
III-III; and IV-IV respectively on Figure 1;
Figure 5 is a cross-section, similar to that of Figure 4, but with the leads formed to extend downwards;
Figures 6a, 6b and 6c are diagrammatic partial cross-sections through one form of hermetic encapsulation, illustrating a problem therewith;
Figures 7a and 7b are similar partial cross-sections, with an alternative design which overcomes the problem illustrated in Figure 5.
Illustrated in Figure 1 is a leadframe indicated generally at 10, with three chip or die positions indicated at 11, 12 and 13. The leadframe has parallel, spaced apart, side members 14 and parallel spaced apart transverse members 15. Members 15 extend between and connect to the side members 14 and define areas 16. At a central position of an area, as seen particularly in position 11, is a die or chip pad 17, the pad being supported from the frame by support leads 18 extending from each corner 19 of the die pad, to each conjunction 20 between a side member 14 and transverse members 15.
Extending between each adjacent pair of support leads 18 is a U-shaped support bar 21, having leg portions 22 connected at their inner ends to the support leads 18 and connected at their outer ends by a lead support portion 25. Extending inward from the lead support portions 25 are leads 26. The inner ends of the leads 26 are adjacent to but spaced from the periphery of the die pad 17. Thus it will be seen that the die pad 17 and the leads 26 and support bar 21 are supported from the frame by the support leads 18. Perforations 27 and 28 extend along each side of the frame, one set of perforations, 27, acting as reference or positioning holes to ensure correct positioning of the frame at process stations.
At position 12, a die or chip 35 is seen positioned on the pad 17. The chip is bonded to the pad, generally by an automated process.
On the upper surface of the chip are contact areas 36. At position 13, wire bonding is shown. Wire connections 37 are made between the contact areas 36 and the inner ends of leads 26.
From the position 13, the frame progresses to an encapsulation apparatus. The frame may proceed to the encapsulation .11~5~6(~
without preForming, or the leads 26 may be preformed. The bend or forming line is indicated by the dotted line 38 at position 13 in Figure 1. Also indicated in Figure 1, are small projections 39 on the leads 26. These projections act as barriers to reduce outflow of plastic material in plastic, or non-hermetic encapsulation.
Figures 2, 3 and 4 illustrate, in cross-section, the leadframe 10 at the various positions 11, 12 and 13 respectively. Figure 5 shows the leads bent or formed, as would be the siutation if done before encapsulation.
The use of the support leads 18 and support bars 21 provides a number of advantages and overcomes many of the problems hitherto experienced. Thus, for prebending, the leads are still interconnected at their outer ends. This prevents distortion of individual leads and also ensures that the leads bend down accurately. Guiding edges on the support bar, indicated by thickened lines 40 in position 13 in Figure 1, ensure that the leads bend down vertically. It is a feature of conventional forms of leadframe that the leads are bent down with non-vertical bending of the leads. While some inclination of the leads can be sometimes accepted, for subsequent automatic assembly, with leads on only two opposite sides of the die pad, this cannot be accepted for leads on all four sides.
Also, whether prebent or bent after encapsulation, electroplating of the leads is made much easier by interconnection of the leads. Further, interconnection of the leads provides protection of the chip from electrostatic discharge damage. After manufacture is complete, the lead support portion is trimmed off. However, whether prebent or not, the encapsulated device is still held in the leadframe, but the leads are ~ 45~60 now electrically isolated from it. Testing of the device can thus be carried out while still in the frame. At the final stage the device is removed from the frame by shearing of the support leads 18.
In many instances it would be convenient, and more economic, to be able to process the frame and attached chip right through encapsulation prior to bending or forming the leads downward. It is easier to traverse a leadframe which is flat, relative to moving such a frame with the leads bent down. Slides are easier to make, and maintain, for a flat strip, whereas for a strip with bent down leads support can mainly only be at the sides of the leadframe. If leads were only on two sides, the lateral sides, no problems occur as grooves can be provided in the sliding surface, but with leads on all sides this cannot be done.
An advantage does occur from pre-bending or forming, in that the bent or formed leads provide self-jigging or alignment of the base with the pad 17. Thus, turning the leadframe over, with the attached chip, 35 underneath, a base can simply be dropped down between the leads, and be in alignment. A further member of simi7ar form to a leadframe, with pre-bent or formed leads, forms a holding and locating member for a top. The leadframe with chip and base is then nested in the holder with the cap, in fact a row of caps, and clips applied to hold the assembly together. The assembly is then fixed to fuse the glass sealing the base and cap together.
Bending after encapsulation can cause problems. In one encapsulation process, for example, the chip with leads is hermetically encapsulated by being enclosed between two housings, for example of ceramic, which are sealed together by fused glass. Due to the brittle nature of the seal, leads are either preformed or bent before sealing, or the leads are clamped betwen the seals and the bent point, but this increases the overall size. The problem is illustrated in Figure 6, (a), (b) and (c). In Figure 6(a), the chip 35 is mounted on the base 46, with a cap 47, of the same external dimensions as the base resting over the base and chip. Prior to assembly a bead of glass exists around the periphery of both base and cap. After attachment of the chip 35, to the pad 17 and attachment of chip pad 17 to the base 46, the cap 47 is positioned on the base. Heating of the assembly causes the glass b~ads to melt and fuse, seali ng the cap and base together and also sealing around the leads 26. This is indicated at 48 in Figure 6(a), and seen enlarged in Figure 6(b). It will be seen that a glass meniscus 4ga and 49b extends between base 46 and leads 26, and between cap 47 and the leads 26 respectively. If the leads are then bent or formed, an incipient crack can form at the join face on the top of the lead, at 50, and chipping occurs at the join face at the bottom or underside of the lead, at 51.
This can lead to eventual failure of the seal.
If the lead is clamped external to the base and cap, the lead being bent down outside the clamp, the above problems can be avoided but the extra room for the clamps, typically .035" between seal and bend, 20 increases the area occupied by the finished package.
Figures 7(a) and 7(b) illustrate a way of overcoming this problem. The cap 47 is made smaller than the base 46. The bead of glass on the base is moved inward slightly and when cap and base are sealed together the meniscus 49b on the top of the lead is spaced inward from the periphery of the base. Typically this distance, X, should be about 1~ to
In the manufacture of semiconductor chips, the chips are mounted on a die pad, and connections made between contact areas on the chip and leads which will eventually be used to connect the final device into a circuit, as by insertion on a printed circuit board (PCB). The chip is packaged, in one of a variety of ways, for example hermetic and non-hermetic encapsulation.
With the extremely large numbers being produced and the need to reduce labour content and to maintain high standards of accuracy and minimal rejection rates, it is favourable to handle assembly in strip form, a leadframe having a number of chip positions, with leads extending from the frame towards a chip mounting position. One such form of leadframe is illustrated and described in U.S. patent no. 4,214,364, issued July 29, 1980~ in the name of the present assignees.
Several problems arise in leadframes, and their use.
Ideally they should be suitable for both hermetic and non-hermetic encapsulation. It would be convenient if the leadframes could be processed with the leads unformed, that is flat and in the same plane as the frame, or with the leads preformed, that is with leg portions bent down. Electroplating is usually carried out on the leg portions.
Protection of the chip from electrostatic discharge during processing is important. Precision forming and cropping is also important and becoming increasingly so with the continual reduction in lead width and closer spacing of leads. Eventually reel to reel automated processing is envisaged and the leadframe should be easily and cheaply manufactured.
The present invention provides a leadframe which provides :1~!L4S~60 for the above problems. A leadframe in accordance with the present invention has parallel, spaced apart, side members and parallel, spaced apart, transverse members. The transverse members extend between, and connect to, the side members, to define a plurality of areas spaced along the frame. A rectangular die or chip pad is positioned centrally in each area with its sides parallel to the side members and transverse members of the frame. A support lead extends from each corner of the die pad to the corresponding conjunction of side and transverse members. A U-shaped support bar extends between each adjacent pair of support leads, the bar including parallel spaced leg portions connected at inner ends to the support leads and connected at outer ends by a lead support portion, the lead support portions parallel to related side and transverse members. A
plurality of leads extend from each lead support portion inwards towards the die pad, with inner ends adjacent to but spaced from the die pad.
The invention will be readily understood by the following description of a particular embodiment, by way of example, in conjunction with the accompanying drawings, in which:-Figure 1 is a plan view of part of a strip of leadframes, with different process steps illustrated at different frames;
Figures 2, 3 and 4 are cross-sections on the lines II-II;
III-III; and IV-IV respectively on Figure 1;
Figure 5 is a cross-section, similar to that of Figure 4, but with the leads formed to extend downwards;
Figures 6a, 6b and 6c are diagrammatic partial cross-sections through one form of hermetic encapsulation, illustrating a problem therewith;
Figures 7a and 7b are similar partial cross-sections, with an alternative design which overcomes the problem illustrated in Figure 5.
Illustrated in Figure 1 is a leadframe indicated generally at 10, with three chip or die positions indicated at 11, 12 and 13. The leadframe has parallel, spaced apart, side members 14 and parallel spaced apart transverse members 15. Members 15 extend between and connect to the side members 14 and define areas 16. At a central position of an area, as seen particularly in position 11, is a die or chip pad 17, the pad being supported from the frame by support leads 18 extending from each corner 19 of the die pad, to each conjunction 20 between a side member 14 and transverse members 15.
Extending between each adjacent pair of support leads 18 is a U-shaped support bar 21, having leg portions 22 connected at their inner ends to the support leads 18 and connected at their outer ends by a lead support portion 25. Extending inward from the lead support portions 25 are leads 26. The inner ends of the leads 26 are adjacent to but spaced from the periphery of the die pad 17. Thus it will be seen that the die pad 17 and the leads 26 and support bar 21 are supported from the frame by the support leads 18. Perforations 27 and 28 extend along each side of the frame, one set of perforations, 27, acting as reference or positioning holes to ensure correct positioning of the frame at process stations.
At position 12, a die or chip 35 is seen positioned on the pad 17. The chip is bonded to the pad, generally by an automated process.
On the upper surface of the chip are contact areas 36. At position 13, wire bonding is shown. Wire connections 37 are made between the contact areas 36 and the inner ends of leads 26.
From the position 13, the frame progresses to an encapsulation apparatus. The frame may proceed to the encapsulation .11~5~6(~
without preForming, or the leads 26 may be preformed. The bend or forming line is indicated by the dotted line 38 at position 13 in Figure 1. Also indicated in Figure 1, are small projections 39 on the leads 26. These projections act as barriers to reduce outflow of plastic material in plastic, or non-hermetic encapsulation.
Figures 2, 3 and 4 illustrate, in cross-section, the leadframe 10 at the various positions 11, 12 and 13 respectively. Figure 5 shows the leads bent or formed, as would be the siutation if done before encapsulation.
The use of the support leads 18 and support bars 21 provides a number of advantages and overcomes many of the problems hitherto experienced. Thus, for prebending, the leads are still interconnected at their outer ends. This prevents distortion of individual leads and also ensures that the leads bend down accurately. Guiding edges on the support bar, indicated by thickened lines 40 in position 13 in Figure 1, ensure that the leads bend down vertically. It is a feature of conventional forms of leadframe that the leads are bent down with non-vertical bending of the leads. While some inclination of the leads can be sometimes accepted, for subsequent automatic assembly, with leads on only two opposite sides of the die pad, this cannot be accepted for leads on all four sides.
Also, whether prebent or bent after encapsulation, electroplating of the leads is made much easier by interconnection of the leads. Further, interconnection of the leads provides protection of the chip from electrostatic discharge damage. After manufacture is complete, the lead support portion is trimmed off. However, whether prebent or not, the encapsulated device is still held in the leadframe, but the leads are ~ 45~60 now electrically isolated from it. Testing of the device can thus be carried out while still in the frame. At the final stage the device is removed from the frame by shearing of the support leads 18.
In many instances it would be convenient, and more economic, to be able to process the frame and attached chip right through encapsulation prior to bending or forming the leads downward. It is easier to traverse a leadframe which is flat, relative to moving such a frame with the leads bent down. Slides are easier to make, and maintain, for a flat strip, whereas for a strip with bent down leads support can mainly only be at the sides of the leadframe. If leads were only on two sides, the lateral sides, no problems occur as grooves can be provided in the sliding surface, but with leads on all sides this cannot be done.
An advantage does occur from pre-bending or forming, in that the bent or formed leads provide self-jigging or alignment of the base with the pad 17. Thus, turning the leadframe over, with the attached chip, 35 underneath, a base can simply be dropped down between the leads, and be in alignment. A further member of simi7ar form to a leadframe, with pre-bent or formed leads, forms a holding and locating member for a top. The leadframe with chip and base is then nested in the holder with the cap, in fact a row of caps, and clips applied to hold the assembly together. The assembly is then fixed to fuse the glass sealing the base and cap together.
Bending after encapsulation can cause problems. In one encapsulation process, for example, the chip with leads is hermetically encapsulated by being enclosed between two housings, for example of ceramic, which are sealed together by fused glass. Due to the brittle nature of the seal, leads are either preformed or bent before sealing, or the leads are clamped betwen the seals and the bent point, but this increases the overall size. The problem is illustrated in Figure 6, (a), (b) and (c). In Figure 6(a), the chip 35 is mounted on the base 46, with a cap 47, of the same external dimensions as the base resting over the base and chip. Prior to assembly a bead of glass exists around the periphery of both base and cap. After attachment of the chip 35, to the pad 17 and attachment of chip pad 17 to the base 46, the cap 47 is positioned on the base. Heating of the assembly causes the glass b~ads to melt and fuse, seali ng the cap and base together and also sealing around the leads 26. This is indicated at 48 in Figure 6(a), and seen enlarged in Figure 6(b). It will be seen that a glass meniscus 4ga and 49b extends between base 46 and leads 26, and between cap 47 and the leads 26 respectively. If the leads are then bent or formed, an incipient crack can form at the join face on the top of the lead, at 50, and chipping occurs at the join face at the bottom or underside of the lead, at 51.
This can lead to eventual failure of the seal.
If the lead is clamped external to the base and cap, the lead being bent down outside the clamp, the above problems can be avoided but the extra room for the clamps, typically .035" between seal and bend, 20 increases the area occupied by the finished package.
Figures 7(a) and 7(b) illustrate a way of overcoming this problem. The cap 47 is made smaller than the base 46. The bead of glass on the base is moved inward slightly and when cap and base are sealed together the meniscus 49b on the top of the lead is spaced inward from the periphery of the base. Typically this distance, X, should be about 1~ to
2 times the lead thickness. The meniscus 49a at the underside of the lead does not reach to the periphery of the base. This is illustrated in 1~L45~6~
Figure 7(a). Figure 7(b) illustrates the situation after bending of the leads. The top meniscus 49b is unaffected by the bending and similarly the bending does not affect the lower meniscus 49a either. This would enable post-encapsulation bending of the leads and facilitate processing of leadframes, particularly reel to reel processing.
While the invention has been described in relation to encapsulation of the type in which the chip is hermetically sealed between glass or ceramic bases and caps, the invention can also be used for plastic encapsulation, where the chip and chip pad are encapsulated by molding of plastic material, for example a synthetic resin around the chip, chip pad, and inner ends of the leads and the wire bonding between chip and leads.
Figure 7(a). Figure 7(b) illustrates the situation after bending of the leads. The top meniscus 49b is unaffected by the bending and similarly the bending does not affect the lower meniscus 49a either. This would enable post-encapsulation bending of the leads and facilitate processing of leadframes, particularly reel to reel processing.
While the invention has been described in relation to encapsulation of the type in which the chip is hermetically sealed between glass or ceramic bases and caps, the invention can also be used for plastic encapsulation, where the chip and chip pad are encapsulated by molding of plastic material, for example a synthetic resin around the chip, chip pad, and inner ends of the leads and the wire bonding between chip and leads.
Claims (10)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A leadframe for leaded semiconductor chip carriers, said lead frame comprising, two parallel, spaced apart side members, a plurality of parallel transverse members extending between the side members and connected thereto to define a plurality of areas spaced along the frame;
a rectangular chip pad positioned centrally in each area, the sides of the pad parallel to the side and transverse members;
a support lead extending from each corner of the chip pad to a corresponding conjunction of a side and a transverse member;
a U-shaped support bar extending between each adjacent pair of support leads, the support bar including spaced parallel leg portions connected at inner ends to the support leads and at outer ends by a lead support portion, the lead support portions parallel to related side and transverse members; and a plurality of leads extending from each lead support portion inwards towards the chip pad, the leads having inner ends adjacent to but spaced from the chip pad.
a rectangular chip pad positioned centrally in each area, the sides of the pad parallel to the side and transverse members;
a support lead extending from each corner of the chip pad to a corresponding conjunction of a side and a transverse member;
a U-shaped support bar extending between each adjacent pair of support leads, the support bar including spaced parallel leg portions connected at inner ends to the support leads and at outer ends by a lead support portion, the lead support portions parallel to related side and transverse members; and a plurality of leads extending from each lead support portion inwards towards the chip pad, the leads having inner ends adjacent to but spaced from the chip pad.
2. A leadframe as claimed in claim 1, including perforations along each side, for positioning of said areas at predetermined positions.
3. A leadframe as claimed in claim 1, including guide edges on said support bar, said guide edges engaging with guide members on a bending apparatus, to ensure correct bending of said leads.
4. A leadframe as claimed in claim 1, including a semiconductor chip mounted on said chip pad.
5. A leadframe as claimed in claim 4, said chip including a plurality of contact areas on an upper surface, and wire bonds extending from the inner ends of the leads to the contact areas.
6. A leadframe as claimed in claim 5, said chip, chip pad and inner ends of said leads encapsulated.
7. A leadframe as claimed in claim 6, said chip, chip pad and inner ends of said leads sealed between a base and a cap.
8. A leadframe as claimed in claim 4, said leads and said support bar, preformed, whereby said leads extend downward normal to the plane of the leadframe, in a direction away from said chip.
9. A leadframe as claimed in claim 1, said leg portions of said support bars connected to said support leads at a position intermediate the ends of the support leads.
10. A leadframe as claimed in claim 1, including lateral projections on said leads, spaced from the inner ends of the leads.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000369692A CA1145860A (en) | 1981-01-29 | 1981-01-29 | Leadframe for leaded semiconductor chip carriers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000369692A CA1145860A (en) | 1981-01-29 | 1981-01-29 | Leadframe for leaded semiconductor chip carriers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145860A true CA1145860A (en) | 1983-05-03 |
Family
ID=4119034
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000369692A Expired CA1145860A (en) | 1981-01-29 | 1981-01-29 | Leadframe for leaded semiconductor chip carriers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1145860A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5094982A (en) * | 1988-02-24 | 1992-03-10 | Fujitsu Limited | Lead frame and method of producing electronic components using such improved lead frame |
-
1981
- 1981-01-29 CA CA000369692A patent/CA1145860A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5094982A (en) * | 1988-02-24 | 1992-03-10 | Fujitsu Limited | Lead frame and method of producing electronic components using such improved lead frame |
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