Semiconductor device with bonding wire reinforcement structure

Abstract

A packaged semiconductor device includes a substrate having input / output (I / O) pads to which a semiconductor die is attached and electrically connected to the substrate via bonding wires. A bonding wire reinforcement structure is formed on the bonding wires before the assembly is covered with a molding compound. The bonding wire reinforcement structure prevents wire sweeping during molding and protects the wires from shorting with other wires. In one embodiment, the bonding wire reinforcement structure is formed of a glass fiber and liquid epoxy resin mixture.

Description

Technical Field

[0001] The present invention relates to integrated circuit (IC) packaging, and more particularly, to a packaged IC having a structure to prevent bond wires from moving during a molding process. Background Art

[0002] Semiconductor dies are becoming more complex, with more circuits being integrated onto the die. As the internal circuits increase, more inputs and outputs (I / Os) are required. To implement packages that use wire-bonded dies and have more I / Os, finer pitches or multiple rows of bonding pads and / or smaller wire diameters are required to prevent the package size from increasing.

[0003] One problem associated with using bonding wires is ensuring that the bonding wires do not touch each other, thereby causing a short circuit condition. Another problem is preventing long wires from sagging so that the wires do not touch the edge of the die. Shorting and sagging can be caused when the wires are bumped or pushed into contact with each other. For example, during molding, as the molding compound enters the mold and flows over the die and bonding wires, the flow or movement of the molding compound can cause the wires to move into contact with each other. This phenomenon is called mold sweeping. Therefore, the wire sweeping problem is exacerbated in cases where the wires are longer, the wire density is greater, and the wire diameter is smaller.

[0004] One method to prevent wire shorting due to wire sweeping is to use insulated wire. However, insulated wire is more expensive than bare wire and may be more difficult to bond to die bond pads or package pads (e.g., lead frame lead ends) due to insulation damage or weakened bonding on the wire ends. Another solution to wire sweeping is to coat the bond wire with liquid epoxy before molding. However, the coating on the wire may become brittle and crack when the package is subjected to cyclic temperature testing.

[0005] Therefore, it is desirable to have a structure for preventing line sweeping during semiconductor device packaging. Summary of the invention

[0006] According to a first aspect of the present invention, there is provided a packaged semiconductor device, comprising:

[0007] a substrate having a plurality of input / output (I / O) pads;

[0008] a semiconductor die having a top active surface and a bottom inactive surface, wherein the bottom surface of the die is attached to the top surface of the substrate;

[0009] a plurality of bond wires electrically connecting die bond pads on the die active surface to corresponding ones of the substrate I / O pads;

[0010] a bond wire reinforcement structure formed on the bond wire; and a molding compound formed on the bond wire, the bond wire reinforcement structure, the top surface of the die, and the top surface of the substrate.

[0011] In one or more embodiments, the bond wire reinforcement structure includes a woven mat formed of a non-conductive material.

[0012] In one or more embodiments, the bond wire reinforcement structure comprises a woven fiberglass mat.

[0013] In one or more embodiments, the bond line reinforcement structure comprises a cellulose nanofiber mat.

[0014] In one or more embodiments, the bonding wire reinforcement structure further includes an epoxy resin formed on the bonding wire.

[0015] In one or more embodiments, the bond wire reinforcement structure is sized and shaped to encase the bond wire.

[0016] In one or more embodiments, at least a portion of each of the substrate I / O pads is exposed to allow external electrical connection to the semiconductor die.

[0017] In one or more embodiments, the substrate includes a metal lead frame.

[0018] In one or more embodiments, the semiconductor die includes at least two semiconductor dies electrically connected to the substrate through bonding wires.

[0019] In one or more embodiments, one of the at least two dies is stacked on top of another of the at least two dies.

[0020] According to a second aspect of the present invention, there is provided a method for assembling a semiconductor device, comprising:

[0021] attaching an inactive side of the semiconductor die to a substrate;

[0022] electrically connecting a die bond pad on an active side of the semiconductor die to a substrate bond pad via a bond wire;

[0023] forming a fiber reinforcement structure on the joining line; and

[0024] The die, the reinforcement structure, and the bonding wires are encapsulated by a molding compound.

[0025] In one or more embodiments, forming the fiber reinforcement structure on the joining line includes:

[0026] forming a premix of the fiber material and the epoxy resin; and

[0027] The premix is ​​applied to the bond wire.

[0028] In one or more embodiments, the fibrous material comprises cellulose nanofibers.

[0029] In one or more embodiments, the fibrous substance comprises glass fibers.

[0030] In one or more embodiments, the premix is ​​applied to the bond wire by spraying the premix onto the bond wire.

[0031] In one or more embodiments, the premix is ​​applied to the bonding wire by dipping the bonding wire into the premix.

[0032] In one or more embodiments, the method further comprises the step of curing the premixture after applying the premixture to the bonding wire.

[0033] In one or more embodiments, forming the fiber reinforcement structure on the joining line comprises:

[0034] placing a mat formed of a non-conductive fiber material over the bond wire; and

[0035] dispensing a liquid epoxy resin onto the fiber mat, wherein the epoxy resin wets the bond line; and

[0036] The wet composition is cured so that the fibers maintain the bond line in a fixed position during the encapsulation step.

[0037] In one or more embodiments, the pad is sized and shaped to cover the bond wire.

[0038] According to a third aspect of the present invention, there is provided a packaged semiconductor device, which is assembled according to the method according to the second aspect of the present invention.

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the accompanying drawings. The present invention is illustrated by way of example and is not limited by the accompanying drawings, in which like reference numerals indicate like elements. It should be understood that the drawings are not drawn to scale and are simplified for ease of understanding of the present invention. For example, the size and dimensions of some elements are exaggerated for ease of understanding and explanation.

[0041] Figure 1 is an enlarged cross-sectional side view of a packaged semiconductor device according to an embodiment of the present invention;

[0042] Figure 2A is an enlarged cross-sectional side view illustrating a method of forming a bonding wire reinforcement structure according to an embodiment of the present invention;

[0043] Figure 2B is an enlarged cross-sectional side view illustrating another method of forming a bond wire reinforcement structure according to an embodiment of the present invention; and

[0044] Figure 2C is an enlarged cross-sectional side view illustrating yet another method of forming a bond wire reinforcement structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The detailed description set forth below in conjunction with the accompanying drawings is intended to be a description of the present preferred embodiments of the present invention, and is not intended to represent the only form in which the present invention can be practiced. It should be understood that the same or equivalent functions can be implemented by different embodiments intended to be encompassed within the spirit and scope of the present invention. In the drawings, the same reference numerals are used throughout to indicate the same elements.

[0046] In one embodiment, the present invention provides a packaged semiconductor device, the packaged semiconductor device comprising a substrate, at least one semiconductor die, a plurality of bonding wires and a bonding wire reinforcement structure. The die is mounted on the top surface of the substrate, and the bonding wires electrically connect the die bonding pads on the active surface of the die to the corresponding I / O pads of the substrate. The bonding wire reinforcement structure is formed on the bonding wires and prevents the bonding wires from moving or shorting with other bonding wires. In one embodiment, a molding compound is formed on the bonding wires, the bonding wire reinforcement structure, the active surface of the die and the top surface of the substrate.

[0047] In another embodiment, the present invention provides a method for assembling a semiconductor device including a bonding wire reinforcement structure. The method includes the following steps: attaching the passive side of a semiconductor die to a substrate, and electrically connecting the die bonding pads on the active side of the semiconductor die to the I / O pads of the substrate via bonding wires. Next, a fiber reinforcement structure is formed on the bonding wires. The reinforcement structure prevents excessive movement of the wires, which may cause short circuits. In one embodiment, the die, reinforcement structure, and bonding wires are covered with a molding compound.

[0048] Reference Figure 1, shows an enlarged cross-sectional side view of one embodiment of a packaged semiconductor device 10 according to an embodiment of the present invention. The device 10 includes a substrate 12 and at least one integrated circuit die 14 mounted on a top surface 16 of the substrate 12. The substrate 12 may include a multilayer wiring board or a metal lead frame, both of which are known in the art. In some embodiments, the packaged device 10 may include one or more additional dies, such as an additional die 18 located on top of the die 14. The die 14 may be any type of die that includes circuitry for performing a predetermined operation, such as a microcontroller, a processor, a mixed signal circuit, a sensor circuit, etc., and any additional die such as the die 18 is the same. The die 14 is generally rectangular and has a top active surface, an opposite bottom, a passive surface, and four side surfaces extending between the top surface and the bottom surface.

[0049] As is known in the art, the die 14 can be attached to the top surface 16 of the substrate 12 (or to a flag of a lead frame) using a die attach epoxy or tape. Where a second die 18 is included, the second die 18 can be attached to the top surface of the first die 14 in a similar manner.

[0050] The die 14 is electrically connected to the substrate 12 via bonding wires 20. More specifically, the bonding pads on the active surface of the die 14 are electrically connected to corresponding substrate bonding pads via bonding wires 20. In one embodiment, the bonding wires include bare copper wires. However, other conductive wires, such as gold wires or silver wires, may be used instead, and the wires may be plated or unplated. It will be appreciated by those skilled in the art that the present invention is not limited to the composition of the wires used, nor to a specific size of the wires, such as wire diameter. If there is a second die, such as die 18, the second die 18 is also electrically connected to the substrate 12 via bonding wires. If the substrate 12 includes a lead frame, the bonding wires 20 extend from the die bonding pads to the bonding locations (typically the inner lead ends) on the leads of the lead frame. In some multi-die packages, the bottom die may be a flip chip die electrically connected to the substrate via bumps rather than bonding wires, while the top die is electrically connected to the substrate via bonding wires.

[0051] A bonding wire reinforcement structure 22 is formed on the bonding wire 20. The bonding wire reinforcement structure 22 includes a woven mat formed of a non-conductive material. In one embodiment, the bonding wire reinforcement structure 22 includes a woven glass fiber mat or a cellulose nanofiber mat. The bonding wire reinforcement structure 22 also includes an epoxy resin formed on the bonding wire 20. The size and shape of the bonding wire reinforcement structure 22 are designed to encase the bonding wire 20.

[0052] Figure 2AA first method of forming a fiber reinforcement structure 22 on a joint line 20 is shown. In this embodiment, a liquid form of the reinforcement structure 22 is sprayed onto the joint line 20 using a nozzle 30. More specifically, a premix 32 of a fiber substance and an epoxy resin is formed, and then the premix 32 is sprayed over and onto the joint line 20 using a spray nozzle 30. In one embodiment, the fiber substance includes cellulose nanofibers. In another embodiment, the fiber substance includes glass fibers.

[0053] In another embodiment, if Figure 2B As shown, the premix 32 is applied to the bond wires 20 by dipping the assembly (substrate, die, and bond wires) into a tray 34 of the premix 32, such as by flipping the assembly over and then dipping the assembly into the tray 34 of the premix 32. In this embodiment, the die 14 may also be covered or partially covered with the premix 32.

[0054] After the premix 32 is applied to the bonding wire 20 , the premix 32 is cured to harden so that the premix 32 holds the bonding wire 20 in place so that the bonding wire 20 does not sweep when the molding process is performed.

[0055] refer to Figure 2C , shows an alternative method of forming a reinforcement structure on the bonding wire 20. In this embodiment, forming a fiber reinforcement structure on the bonding wire includes placing a mat 36 formed of a non-conductive fiber material on the bonding wire 20 and then dispensing a liquid epoxy resin onto the fiber mat 36. Figure 2A The liquid epoxy is dispensed onto the mat 36 using a spray nozzle as shown, or by other methods, such as using a syringe-type dispensing device (not shown). The liquid epoxy wets the fiber mat 36, causing the fiber material to form itself on and around the wire 20. The wet composition is then cured, causing the fibers to hold the bond wire 20 in place during the subsequent encapsulation step.

[0056] Preferably, the pad is sized and shaped to cover the bond wire 20. In the currently preferred embodiment, the pad 36 includes a center cutout so that the pad 36 does not cover the center top surface of the die 14 (and / or 18). The center cutout is intended to prevent air bubbles from being trapped under the pad 36.

[0057] Reference again Figure 1In the current preferred embodiment, the packaged semiconductor device 10 also includes a molding compound 24 formed on the bonding wires 20, the bonding wire reinforcement structure 22, the top surface of the tube core 14 (and / or the tube core 18), and the top surface 16 of the substrate 12. The molding compound 24 protects the tube core 18 and the wires 20 from being contaminated or damaged, for example, due to exposure to the environment. The encapsulation process is well known. A common method used in semiconductor device assembly is transfer molding, which allows small and complex components to be molded. Transfer molding includes two basic stages. First, the component to be encapsulated is placed in the mold cavity, and then the molding compound 24 that has been changed into liquid form by heating is pressed into the cavity. Next, the molding compound 24 is allowed to solidify, thereby forming the packaged device 10. During the molding process, the wires are prevented from sweeping by the bonding wire reinforcement structure 22.

[0058] In one embodiment, as discussed above, the bond wire reinforcement structure 22 comprises an epoxy resin and a fiber material. In a currently preferred embodiment, the molding compound 24 comprises the same material as the epoxy resin used to form the bond wire reinforcement structure 22. This allows the materials to mix, and therefore when hardened, there is no CTE mismatch between the materials. If a fiber mat 36 is used, the fibers may include glass fibers formed of silicon dioxide (Si) and composite fillers also formed of silicon dioxide. The composition of the epoxy resin may then be adjusted to prevent stress caused by material mismatch. Using a spray and impregnation process ( Figure 2A and 2B ), preferably with a minimal amount of coating on the bond line.

[0059] To avoid mold void traps, vacuum molding can be used to remove air during cavity filling.

[0060] exist Figure 1 In the embodiment shown in , conductive balls 26 are attached to the bottom surface of substrate 12. As will be appreciated by those skilled in the art, conductive balls 26 are attached to substrate pads (not shown) that are electrically connected to pads on the opposite side of the substrate to which bond wires 20 are attached, such that conductive balls 26 allow electrical connection to die 14 and 18. For a leadframe-based package (i.e., substrate 12 includes a leadframe), conductive balls 26 are not required because the outer ends of the leads are exposed to make electrical connection to die 14 and 18.

[0061] As is apparent from the above discussion, the present invention provides a semiconductor device and a method of assembling a semiconductor device. The present invention mitigates line sweeping and line shorting, and facilitates very fine pitch requirements. Therefore, more intricate line layouts for higher I / O devices are possible, and longer lines can also be used. The present invention allows for higher line counts, higher line density, and smaller diameter lines. Because the lines are surrounded by a reinforcement structure, there is also less likelihood of foreign matter being caught between the lines.

[0062] In addition, the package structure eliminates the need for package-level aging and cold / hot testing, which can significantly reduce assembly and testing costs and shorten cycle time. The present invention reinforces conformal wire coating to achieve good sealing and insulation of the wire.

[0063] The description of the preferred embodiments of the present invention has been presented for the purpose of illustration and description, but is not intended to be exhaustive or to limit the invention to the disclosed forms. It will be appreciated by those skilled in the art that changes may be made to the above-described embodiments without departing from the broad inventive concept thereof. Therefore, it will be understood that the present invention is not limited to the specific embodiments disclosed, but encompasses modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A packaged semiconductor device, characterized in that: include: A substrate having a plurality of input / output I / O pads; a semiconductor die having a top active surface and a bottom inactive surface, wherein the bottom surface of the die is attached to the top surface of the substrate; a plurality of bond wires electrically connecting die bond pads on the die active surface to corresponding ones of the substrate I / O pads; a bonding wire reinforcement structure formed on the bonding wire; as well as a molding compound formed on the bond wires, the bond wire reinforcement structure, the top surface of the die, and the top surface of the substrate; The bonding wire reinforcement structure includes a woven mat formed of a non-conductive material.

2. The packaged semiconductor device according to claim 1, wherein: The bond wire reinforcement structure includes a woven fiberglass mat.

3. The packaged semiconductor device according to claim 1, wherein: The bond line reinforcement structure includes a cellulose nanofiber mat.

4. The packaged semiconductor device according to claim 1, wherein: The bonding wire reinforcement structure further includes an epoxy resin formed on the bonding wire.

5. The packaged semiconductor device according to claim 1, wherein: The bond wire reinforcement structure is sized and shaped to encase the bond wire.

6. The packaged semiconductor device according to claim 1, wherein: At least a portion of each of the substrate I / O pads is exposed to allow external electrical connection to the semiconductor die.

7. The packaged semiconductor device according to claim 1, wherein: The semiconductor dies include at least two semiconductor dies electrically connected to the substrate by bonding wires.

8. A method for assembling a semiconductor device, characterized in that: include: attaching an inactive side of the semiconductor die to a substrate; electrically connecting a die bond pad on an active side of the semiconductor die to a substrate bond pad via a bond wire; forming a fiber reinforcement structure on the bond wire, the fiber reinforcement structure comprising a woven mat formed of a non-conductive material; as well as The die, the reinforcement structure, and the bonding wires are encapsulated by a molding compound.

9. A packaged semiconductor device, characterized in that: Assembled according to the method of claim 8.

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