Integrated circuit package containing inwardly bent leads

Abstract

The present invention provides a packaged semiconductor device (100), comprising: a semiconductor die (180) mounted on a lead frame; a housing (120) for the semiconductor die, the housing defining a horizontal plane and a horizontal direction. The lead frame comprises leads (102, 103, 108, 109), each lead having an inner lead portion and an outer lead portion inside the housing, the outer lead portion comprising a first portion (102a, 103a, 108a, 109a) extending from one of the side walls (120c, 120d) of the housing along the horizontal direction, a transition portion (102b, 103b, 108b, 109b) comprising a vertical component, and a distal portion (102c, 103c, 108c, 109c), wherein the distal portion of the lead is entirely on the horizontal plane. The outer lead portions alternate between gull-wing lead shapes (103, 109) having the distal portions extending outwardly from the housing in the horizontal direction and inwardly extending leads (102, 108) having their distal portions extending inwardly toward the housing in the horizontal direction. The lead frame is composed of a single lead frame.

Description

Technical Field

[0001] The present invention relates to lead arrangements for integrated circuit (IC) packages. Background Art

[0002] A variety of semiconductor IC packages are known that provide support for at least one IC die, provide protection from environmental influences, and enable the IC die to be surface mounted on a printed circuit board (PCB) and interconnected with the printed circuit board. One conventional package configuration includes a lead frame having a die pad and a plurality of leads surrounding the die pad. For plastic packaging, after IC die bonding in a top-side up manner, usually followed by wire bonding, or after flip chip mounting in a top-side down manner, a molding process is then performed by using the lead frame to form a molded housing, so that the semiconductor package can be obtained by cutting and trimming the leads protruding outside the housing.

[0003] The gull-wing leads extend out of the housing generally horizontally from the sidewall surface of the packaging material, then extend downward along a diagonal path having horizontal and vertical components, and then extend out again in a horizontal direction to provide a distal portion suitable for soldering to a PCB. Gull-wing leads are commonly used on surface mounted chips, such as quad flat packages (QFP) and small outline integrated circuits (SOIC). Gull-wing packages are known to provide superior self-alignment performance based on the surface tension of molten solder during package installation on a customer's PCB, even with some displacement, compared to flat lead packages.

[0004] It is known that small-profile gull-wing IC packages are limited in functional density (i.e., their pin count) by standardized PCB pad pattern spacing requirements. There is a growing demand to allow more pins (or leads) in a given circuit board area without increasing PCB manufacturing complexity (pin-to-pin or lead-to-lead spacing) and the overall size of the package. The affected package types include SOIC, small outline package (SOP), micro outline package (MSOP), shrink small outline package (SSOP), thin small outline package (TSOP), thin shrink small outline package (TSSOP), small outline transistor (SOT) and thin small outline transistor (TSOT). Conventional SOP gull-wing packages have a pin pitch of 0.4 mm (TSSOP) to 0.95 mm (SOT) and a pin width of 0.2 mm to 0.5 mm. The extended lead portions of all leads from all such packages are in the same gull-wing shape. Summary of the invention

[0005] This Summary is provided to introduce in a simplified form a brief selection of disclosed concepts that are further described below in the Detailed Description including the provided figures. This Summary is not intended to limit the scope of the claimed subject matter.

[0006] The disclosed aspects include a leadframe design having gull-wing leads alternating with inward-bending leads having their distal flat (horizontal) end portions bent inwardly toward the body of the package. It has been recognized that bending the alternating leads with their distal portions bent toward the body, rather than all bent outwardly as conventionally as gull-wing leads, allows us to increase the lead (or pin) density while maintaining the same lead width and reasonable lead pitch. The inward-bending leads can optionally extend below the package body.

[0007] A packaged semiconductor device comprises: a semiconductor die mounted on a lead frame; a housing for the semiconductor die, the housing defining a horizontal plane and a horizontal direction. The lead frame comprises leads, each lead having an inner lead portion and an outer lead portion inside the housing, the outer lead portion comprising a first portion extending from one of the side walls of the housing in the horizontal direction, a transition portion comprising a vertical component, and a distal portion, wherein the distal portion of the lead is entirely in the horizontal plane. The outer lead portion alternates between a gull-wing lead shape having the distal portion extending outward from the housing in the horizontal direction and an inwardly extending lead having its distal portion extending inwardly toward the housing in the horizontal direction. The lead frame is composed of a single lead frame. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0009] Figure 1 is a cross-sectional view of an example packaged semiconductor device having gull-wing leads alternating with inwardly bent leads having their distal ends bent inwardly toward the body of the package, with bond pads on the IC being wire-bonded to the leads.

[0010] Figure 2A yes Figure 1 0013] A bottom view of a packaged semiconductor device is shown in FIG. 10 with distal ends of inwardly bent leads optionally extending below a housing, again. Figure 2B yes Figure 1 A is a side view of a packaged semiconductor device. Figure 2C yes Figure 1 A is a top perspective view of an example packaged semiconductor device. Figure 2D yes Figure 1 A bottom perspective view of an example packaged semiconductor device shown in FIG.

[0011] Figure 3A is a bottom perspective view of a packaged device having its inwardly bent even-numbered leads bent under the housing and connected together on each side to provide better thermal performance according to example aspects. Figure 3B is a bottom perspective view of a packaged device having its inwardly bent even-numbered leads bent under a die pad to provide better thermal performance according to example aspects.

[0012] Figure 4 is a partially exposed top perspective view of an example packaged semiconductor device showing solder features illustrated as a flip chip on leads (FCOL) bonding arrangement in which solder features on bond pads of a semiconductor die contact corresponding gull-wing leads alternating with inwardly bent leads.

[0013] Figures 5A to 5D Steps are shown in an example method for forming a disclosed packaged semiconductor device having a leadframe including gull-wing leads alternating with inwardly bent leads.

[0014] FIG. 6A shows the footprint of a pad for a PCB having a through-hole pad for mounting the leads of a conventional 8-pin TSSOP package, with some example spacing distances shown, and FIG. Figure 6B The pad footprint of another PCB is shown with staggered pads for mounting the leads of the disclosed 10-lead TSSOP package with alternating leads that are inwardly bent leads, demonstrating that we can increase the lead spacing while increasing the lead count.

[0015] Figure 6C exhibit Figure 2A The disclosed IC package shown in D has a Figure 6B The staggered configuration on the PCB shown in FIG. 1 shows alternating inwardly bent leads mounted to pads. DETAILED DESCRIPTION

[0016] Example aspects are described with reference to the accompanying drawings, wherein similar reference numerals are used to designate similar or equivalent elements. The ordering of the actions or events described should not be considered restrictive, as some actions or events may occur in different orders and / or occur simultaneously with other actions or events. In addition, some of the described actions or events may not be required to implement the method according to the present invention.

[0017] Figure 1 1 is a cross-sectional view of an example packaged semiconductor device 100 having gull-wing leads shown as 103 and 109 alternating with inwardly bent leads 102 and 108 having their distal end portions 102c, 108c bent inwardly toward a housing 120 of the package (a molded housing is shown) with bond pads 180a on a semiconductor die 180 being wire-bonded to the respective leads by bonding wires 161. The leads are also all on the same horizontal plane inside the housing 120 because they are formed from the same sheet of metal. The following description of the Figure 4An alternative FCOL bonding arrangement is shown.

[0018] Semiconductor die 180 is shown with its bottom side attached to die pad 121 by die attach material 181 (e.g., epoxy). Semiconductor die 180 may be an IC or a discrete device die, such as a power transistor. Semiconductor die 180 may be multiple dies (stacked or sideways) and may include sensors or passive components (e.g., non-semiconductors such as capacitors, resistors, inductors). Although housing 120 is Figure 1 1 is shown as a molded housing, but more generally, the housing 120 may also include a ceramic housing. The housing 120 has a top surface 120a and a bottom surface 120b that each define a horizontal plane and a direction within the horizontal plane, and includes a first sidewall 120c and at least a second sidewall 120d opposite the first sidewall between the bottom surface 120b and the top surface 120a.

[0019] The outer lead portions alternate between gull-wing lead shapes (described as leads 103 and 109 for odd-numbered leads) with their distal portions 103c and 109c extending horizontally outward from the housing 120, and inwardly bent leads (described as even-numbered leads 102 and 108) with their distal portions 102c and 108c extending horizontally inward toward the housing material 120. Alternatively, because the terms 'even' and 'odd' are interchangeable as used herein (so long as the leads alternately bend inwardly and outwardly), the gull-wing leads may be the even-numbered leads and the inwardly bent leads may be the odd-numbered leads.

[0020] The inwardly bent leads 102, 108 are seen to be C-shaped or J-shaped. The distal end portions 102c, 108c of the inwardly bent leads 102, 108 are shown as optionally extending below the housing 120. The leadframe is comprised of a single leadframe. The disclosed leadframes are single leadframes meaning that they are single (or unitary) pieces of the same material (e.g., copper) entirely devoid of any joints, adhesives, or bonding materials that bond otherwise separate leadframe pieces together, making the disclosed leadframes distinct from bonded leadframe arrangements in which two stacked leadframes are bonded to each other by an adhesive material.

[0021] The leads each have an inner lead portion and an outer lead portion within the housing 120, the outer lead portion including a first portion 102a, 103a, 108a, 109a extending in a horizontal direction from one of the first side wall 120c and the second side wall 120d, a transition portion 102b, 103b, 108b and 109b including a vertical component, and a distal portion 102c, 103c, 108c and 109c. The distal portions 102c, 103c, 108c and 109c are all on the same horizontal plane defined by the top surface 120a and the bottom surface 120b of the housing 120. As used herein, being on the same horizontal plane means being at substantially the same height along the z (height) direction orthogonal to the horizontal direction, and is defined herein as an average height from a reference plane that is all no more than ±0.1 mm (about 4 mils). For example, the top surfaces of distal portions 102c, 103c, 108c and 109c have a minimum distance of zero (contacting the bottom of housing 120 for non-exposed die pads) to a maximum distance of 3 / 4 of the thickness of the lead frame material (typically from 4 mils to 8 mils), which is therefore calculated to be a maximum of 3 mils (0.076 mm) to 6 mils (0.152 mm) from the bottom surface 120b of housing 120.

[0022] In the case of an exposed die pad on the bottom of the package, the inward bend leads will not extend under the die pad, and the vertical offset distance between the bottom surface 120b of the die pad and the bottom of the distal ends of the inward bend leads should be close to zero on the base plane, defined herein as within 1 mil (0.025 mm). For the bottom exposed die pad configuration, this close to zero vertical offset between the bottom of the die pad and the inward bend leads is to ensure that reliable solder interconnections can be made between both the inward bend leads and the exposed die pad to the corresponding pads on the PCB.

[0023] The use of only one lead frame for the entire packaged device 100 enables all leads to be manufactured using one standard thickness lead frame, which are located at the same level inside the housing (due to being formed from the same metal sheet), exit the housing 120 of the package horizontally at substantially the same plane (height), and remain in the same plane all the way to the ends of their distal portions 102c, 103c, 108c, and 109c. This aspect simplifies the package design and reduces assembly costs by enabling the application of solder at the same height (typically soldering the distal portions 102c, 103c, 108c, and 109c to the PCB).

[0024] Figure 2A yes Figure 1, with distal portions 102c, 103c, 108c, and 109c of inwardly bent leads 102, 104, 108, and 110 extending, again optionally, below bottom surface 120b of housing 120. Gull-wing leads are shown as 101, 103, 105, 107, 109, and 111. Figure 2B yes Figure 1 FIG. 1 is a side view of a packaged semiconductor device 100 shown in FIG. Figure 2C yes Figure 1 00 , showing distal portions 101 c , 102 c , 103 c , 105 c , 107 c , 109 c , and 111 c . Figure 2D yes Figure 1 0 is a bottom perspective view of the example packaged semiconductor device 100 shown in , showing distal portions 101c, 102c, 103c, 104c, 105c, 106, 107c, 108c, 109c, 110c, and 111c.

[0025] Figure 3A is a bottom perspective view of a packaged device 300 having its inwardly bent even-numbered leads 102 and 104 and 108 and 110 bent under housing 120 and connected together on each side to provide better thermal performance, according to example aspects. Figure 3B 3 is a bottom perspective view of a packaged device 350 having its even-numbered leads 102 and 104 and 108 and 110 bent under the die pad 121 bent inward to provide better thermal performance, according to example aspects. Also, there may be lead bends to allow the inwardly bent leads to contact the die pad prior to molding by utilizing conventional tie bars or by adding metal connectors after the lead bends prior to molding.

[0026] Figure 4 4 is a top perspective view of a partially exposed example packaged semiconductor device 400 to show solder features 418 shown as a FCOL bonding arrangement, where solder features 418 on bond pads of semiconductor die 180 contact respective leads shown as leads 401, 402, 403, 407, 408, and 409. The solder features may include solder balls or solder cap (e.g., copper) posts. Inwardly bent leads are shown as 402 and 408 and gull-wing leads are shown as 401, 403, 407, and 409.

[0027] Figures 5A to 5DSteps in an example method for forming a disclosed packaged semiconductor device having a lead frame including gull-wing leads alternating with inwardly bent leads are shown. Typically, there will be only limited required changes to the packaged device assembly process. The disclosed method can typically reuse all of the same steps in current packaged device assembly processes, with one additional step during formation being to bend the even-numbered leads inwardly, as described below in Figure 4 C. Lead bending may start from a conventional arrangement comprising a leadframe sheet having a plurality of leadframes, each leadframe having a plurality of linear leads extending from sidewalls of encapsulation material of an IC package mold housing shown on at least 2 sides of the IC package.

[0028] Figure 5A An example lead bending apparatus is shown prior to lead bending, comprising a clamp 510, which may be a standard clamp, comprising anvil portions 515a and 515b (see Figure 5B The disclosed anvil 515 ( Figure 5D ) and includes punch 1 520a and punch 2 520b (see Figure 5C The disclosed punch 2 (520b) in FIG. Figure 5B A clamp 510, anvil 515, and punch 1 520a of a pin bending apparatus are shown configured for a first bending step for bending, wherein the outer lead portions of the odd-numbered leads are intended to be gull-wing leads and the outer lead portions of the even-numbered leads are intended to be inwardly bent leads. The anvil 515 is shown modified between contacting alternating odd-numbered leads, shown as anvil portions 515a, and even-numbered leads, shown as anvil portions 515b, and the direction of the punch 1 520a is shown to move downward in a vertical direction.

[0029] The anvil 515 is thus modified to contact alternating leads (even and odd), with one anvil portion 515a being configured to handle the odd leads to provide a gull wing shape (two 90 degree curves), and the other anvil portion set 515b being configured to provide only one substantially 90 degree curve. The even leads include a second bending step to bend them inwardly toward the housing 120. Figure 5C In the second bending step shown in FIG. 5 , the punch 2 520 b is guided to bend the ends of the even-numbered leads inwardly toward the housing 120 in the horizontal (xy) plane. Figure 5DAnother view of an example lead bending apparatus is shown with two punches (punch 1 520a applied to all leads and punch 2 520b applied only to leads intended to bend the leads inwardly. Although the anvil is shown as 515, as described above, the anvil 515 is modified between contacting alternating odd-numbered pins shown as anvil 515a and even-numbered pins shown as anvil 515b, and the direction of punch 1 520a is moved downward in the vertical direction as shown.

[0030] The disclosed leadframe lead bending can be applied to a variety of leadframe types, including stamped and etched leadframes, rough and smooth leadframes, and leadframes with or without coatings / platings. Typically no changes to packaging and shipping media or processes (same tube, tape / reel, etc.) are required.

[0031] The disclosed aspects can be integrated into a variety of assembly processes to form a variety of different semiconductor IC devices and related products. The assembly may include a single semiconductor die or multiple semiconductor dies, such as a PoP configuration including multiple stacked semiconductor dies. A variety of packaging substrates can be used. The semiconductor die may include various elements therein and / or layers thereon, including barrier layers, dielectric layers, device structures, active elements and passive elements, including source regions, drain regions, bit lines, bases, emitters, collectors, conductive lines, conductive vias, etc. In addition, semiconductor dies can be formed by a variety of processes including bipolar, insulated gate bipolar transistors (IGBTs), CMOS, BiCMOS, and MEMS.

[0032] Examples

[0033] The disclosed aspects are further illustrated by the following specific examples, which should not be construed in any way as limiting the scope or content of the invention.

[0034] 6A shows the footprint of land pads 601 - 608 of a PCB configured with in-line land pads for mounting the leads of a conventional 8-pin TSSOP package, with some example spacing distances shown. Figure 6B The footprint of pads 651-655 and 657-661 of another PCB is shown, which is configured with staggered pads for mounting the leads of the disclosed 10-pin TSSOP package with alternating leads as inwardly bent leads, which shows that we can increase the lead spacing while increasing the lead count. As described above, the inner pads can be shorted together to enhance thermal or electrical performance. The pads on the PCB are usually further routed to contact other components on the PCB.

[0035] PCBs can be in a variety of configurations, including multi-layer, flexible or rigid, ceramic or metal clad. Solder or other conductive attachment material (e.g., solder) typically electrically and mechanically connects the leads of the package to the pads of the PCB. Results show that by using the disclosed leadframe including gull-wing leads alternating with inwardly bent leads, we can increase the lead spacing from 0.20 mm to 0.24 mm while also increasing the package lead count from 8 pins to 10 pins. Figure 6C exhibit Figure 2A The disclosed IC package shown in D has a Figure 6B The staggered configuration shown in FIG. 6 shows alternating inwardly bent leads mounted to solder pads 651 to 655 and 657 to 661 of PCB 650.

[0036] Those skilled in the art to which the present invention relates will appreciate that numerous variations of the disclosed aspects are possible within the scope of the claimed invention, and that further additions, deletions, substitutions and modifications may be made to the above-described aspects without departing from the scope of the present invention.

Claims

1. A packaged semiconductor device, comprising: a semiconductor die having topside bond pads mounted on a lead frame; A housing for the semiconductor die, the housing having a bottom surface and a top surface defining a horizontal plane and a horizontal direction, and including a first sidewall and at least a second sidewall opposite to the first sidewall between the bottom surface and the top surface; The lead frame comprises: a plurality of leads, each lead having an inner lead portion and an outer lead portion within the housing, the outer lead portion comprising a first portion extending from one of the first and second side walls along the horizontal direction, a transition portion comprising a vertical component, and a distal portion, wherein the distal portions of the plurality of leads are all on the horizontal plane; and wherein the outer lead portion alternates between a gull-wing lead shape having the distal portion extending outward from the housing along the horizontal direction and an inwardly extending lead having the distal portion extending inward toward the housing along the horizontal direction and completely below the bottom surface of the housing, and wherein the first portion of the outer lead portion having the gull-wing lead shape extends a first distance along the horizontal direction, and the first portion of the outer lead portion having the inwardly extending lead extends a second distance along the horizontal direction that is different from the first distance. 2 . The packaged semiconductor device of claim 1 , wherein at least two of the distal end portions of the inwardly extending leads are connected together adjacent the bottom surface. The packaged semiconductor device of claim 1 , wherein the distal portion extends below the housing. 4 . The packaged semiconductor device of claim 1 , wherein the semiconductor die is mounted on the plurality of leads in a flip chip on leads (FCOL) configuration. The packaged semiconductor device of claim 1 , wherein the housing comprises a molded housing. 6 . The packaged semiconductor device of claim 1 , wherein the bonding pads of the semiconductor die are flip-chip attached to the inner lead portions.

7. The packaged semiconductor device of claim 1, wherein the lead frame further comprises a die pad, and wherein the semiconductor die is mounted on the die pad with its top side facing up, further comprising a bonding wire between the bonding pad and the inner lead portion. 8 . The packaged semiconductor device of claim 1 , wherein the inwardly extending leads are C-shaped or J-shaped. 9 . The packaged semiconductor device of claim 1 , wherein a bottom surface of the distal portion is entirely within a fixed distance of ±0.1 mm measured from the bottom surface of the housing. 10 . The packaged semiconductor device of claim 1 , wherein the first portion of the outer lead portion of each of the plurality of leads extends from one of the first and second sidewalls along the horizontal direction along a same horizontal plane.

11. A leadframe configured for a packaged semiconductor device, the packaged semiconductor device comprising semiconductor die, the semiconductor die comprising a housing having a first sidewall and at least a second sidewall opposite the first sidewall, wherein at least one semiconductor die has a topside bond pad therein, the leadframe comprising: a plurality of leads, each lead having an inner lead portion and an outer lead portion within the housing, the outer lead portion comprising a first portion extending horizontally from one of the first and second side walls, a transition portion comprising a vertical component, and a distal portion, wherein the distal portions of the plurality of leads are all in a horizontal plane; and wherein the outer lead portion alternates between a gull-wing lead shape having the distal portion extending outward from the housing along the horizontal direction and an inwardly extending lead having the distal portion extending inward toward the housing along the horizontal direction and completely below the bottom surface, and wherein the first portion of the outer lead portion having the gull-wing lead shape extends a first distance along the horizontal direction, and the first portion of the outer lead portion having the inwardly extending lead extends a second distance along the horizontal direction that is different from the first distance.

12. The lead frame of claim 11, wherein at least two of the distal end portions of the inwardly extending leads are connected together adjacent the bottom surface. The lead frame of claim 11 , wherein the distal portion extends below the housing.

14. The lead frame of claim 11, wherein the bond pads of the semiconductor die are flip-chip attached to the inner lead portions.

15. The lead frame of claim 11, wherein the lead frame further comprises a die pad, and wherein the semiconductor die is mounted on the die pad with its top side facing up, further comprising a bonding wire between the bonding pad and the inner lead portion.

16. The lead frame of claim 11, wherein the inwardly extending leads are C-shaped or J-shaped. 17 . The lead frame of claim 11 , wherein the bottom surface of the distal end portion is entirely within a fixed distance of ±0.1 mm measured from the bottom surface of the housing.

18. The lead frame of claim 11, wherein the first portion of the outer lead portion of each of the plurality of leads extends from one of the first and second side walls along the same horizontal plane in the horizontal direction.

19. A method of assembling a packaged semiconductor device, comprising: mounting a semiconductor die having a top side bond pad on a lead frame having a plurality of leads, each lead having an inner lead portion inside a housing for the semiconductor die, the housing having a bottom surface and a top surface defining a horizontal plane and a horizontal direction, including a first sidewall between the bottom surface and the top surface and at least a second sidewall opposite the first sidewall, and an outer lead portion extending outside the housing and terminating at a distal lead portion; lead bending outer lead portions of the plurality of leads to alternately form gull-wing lead shapes and inwardly extending leads having distal ends that bend inwardly toward the housing and completely below the bottom surface of the housing; and Wherein the distal portions of all the outer lead portions are on the horizontal plane, and wherein the first portion of the outer lead portion having the gull-wing lead shape extends a first distance along the horizontal direction, and the first portion of the outer lead portion having the inwardly extending lead extends a second distance along the horizontal direction that is different from the first distance.

20. A method according to claim 19, wherein the lead bending includes using a lead bending apparatus including a clamp, an anvil and a punch, wherein the anvil is modifiable to contact alternating leads, wherein in a first lead bending step, one anvil arrangement is used to provide the gull-wing lead shape, and another anvil arrangement is configured to provide only a substantially 90 degree curve to the subsequently formed inwardly extending lead, and further includes a second bending step to selectively bend the lead having the substantially 90 degree curve inwardly toward the housing to complete the inwardly extending lead.

21. The method of claim 19, wherein the inwardly extending leads are C-shaped or J-shaped.

22. The method of claim 19, further comprising connecting the plurality of leads to solder pads of a printed circuit board (PCB) in a staggered configuration.

23. The method of claim 19, wherein each of the lead portions exits the housing in the horizontal direction from one of the first and second side walls along a same horizontal plane.

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