Die attach method for semiconductor devices and corresponding semiconductor devices

Abstract

Embodiments of the present disclosure relate to die attach methods for semiconductor devices and corresponding semiconductor devices. Manufacturing a semiconductor device, such as an integrated circuit, includes providing a leadframe having a die pad region, attaching one or more semiconductor dies onto the die pad region of the leadframe via a soft solder die attach material, and forming a device package by molding a package material onto the semiconductor dies attached onto the die pad region of the leadframe. An enhancement layer provided onto the leadframe to counteract delamination of the device package is selectively removed from the die pad region via laser beam ablation, and the semiconductor dies are attached onto the die pad region via the soft solder die attach material provided at where the enhancement layer has been removed to improve wettability of the soft solder material.

Description

TECHNICAL FIELD

[0001] The present specification relates to manufacturing semiconductor devices.

[0002] One or more embodiments can apply to manufacturing integrated circuits (ICs). BACKGROUND

[0003] Providing improved resistance to delamination of the package for a packaged semiconductor device represents a development trend in manufacturing semiconductor devices, e.g. for the automotive domain.

[0004] A method providing such a desired feature involves forming a so-called enhancement layer having increased affinity with the package molding compound (e.g. an epoxy molding compound).

[0005] Note that such an enhancement layer can negatively impact the process of attaching a semiconductor die on the die pad area of a leadframe, e.g. via soft solder.

[0006] Attempts have been made to solve this problem by modifying the soft solder die attach parameters (high temperature, high air forming gas flow, etc.) without finding a significant improvement. SUMMARY

[0007] One or more embodiments can relate to a semiconductor device (e.g. an integrated circuit).

[0008] One or more embodiments can relate to a (selective) removal of the enhancement layer via laser beam ablation in order to restore the wettability of the underlying material (e.g. silver), which facilitates the attachment of soft solder dies.

[0009] One or more embodiments can rely on the recognition that the current method of providing an enhancement layer is by processing a silver layer (silver dots) provided on the base metal material (e.g. copper) of the leadframe. Laser ablation of such an enhancement layer (oxidized silver) was found to result in a “clean” surface that is modified (melted and / or refined) in a way that (further) facilitates soft solder die attachment. BRIEF DESCRIPTION OF DRAWINGS

[0010] One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0011] - Figure 1 is an exemplary representation of a semiconductor device suitable for manufacturing according to an embodiment,

[0012] - Figure 2 is an example of a possible action in an embodiment, and

[0013] - Figure 3 substantially corresponds to a cross-sectional view along Figure 2 line III-III in Fig. 3. Detailed Implementation

[0014] In the following description, one or more specific details are set forth, which are intended to provide a thorough understanding of examples of the embodiments. Embodiments may be obtained without one or more of these specific details, or by utilizing other methods, components, materials, etc. In other instances, known structures, materials, or operations are not illustrated or described in detail so that certain aspects of the embodiments will not be obscured.

[0015] References to "embodiment" or "one embodiment" within the framework of this specification are intended to indicate that a particular configuration, structure, or feature described with respect to that embodiment is included in at least one embodiment. Therefore, phrases such as "in an embodiment" or "in one embodiment" appearing at one or more points in this specification do not necessarily refer to the same embodiment. Furthermore, in one or more embodiments, particular configurations, structures, or features may be combined in any suitable manner.

[0016] The reference numerals used herein are provided solely for convenience and are therefore not intended to limit the extent of protection or the scope of the embodiments.

[0017] Figure 1 This is a schematic representation of a semiconductor device 10, such as an integrated circuit, as viewed in a plan (top view).

[0018] The semiconductor device 10 illustrated herein includes a so-called leadframe 12 and (at least) a semiconductor chip or die 16, the so-called leadframe 12 having (e.g., a central) die pad region 14, and (at least) a semiconductor chip or die 16 being attached to the die pad region 14 of the leadframe 12 via a soft soldering process.

[0019] Package 18 can be molded onto a semiconductor die 16 attached to a die pad area 14 of leadframe 12 to provide a device package having an external (remote) tip of a lead protruding from package 18 in leadframe 12.

[0020] like Figure 1 Some general structures and manufacturing processes of the semiconductor device 10 illustrated herein (such as the provision of various additional components, such as wire bonding that couples the leads of the lead frame to the semiconductor die, etc., not visible in the figures) are well known to those skilled in the art, which makes it unnecessary to provide a more detailed description of the known parts of the structure and process herein.

[0021] Conventional solutions for manufacturing devices such as the semiconductor device 10 illustrated herein may involve providing the lead frame 12 in the form of a (strip) strip of a metallic material (such as copper). Such a strip may be included in...Figure 2 The plurality of segments indicated with 13 each comprise a respective die pad area 14 onto which a respective semiconductor die can be attached.

[0022] The individual segments of the strip-like structure can be finally separated ("singulated") before or after molding of the respective package 18 to provide individual devices.

[0023] Figures 1-3 A metal coating 20 is shown wetted onto the leadframe. The metal coating 20 is a different metal than the metal of the leadframe 12, such as silver for a copper leadframe. The metal coating 20 serves to improve the bonding of the solder applied to the lower surface of the semiconductor chip or die 16 onto the die pad area 14 of the leadframe 12.

[0024] The process further involves forming an enhancement layer 22 on the upper surface of the metal coating. The enhancement layer 22 has a higher affinity with the molding compound 18 which is eventually molded onto the leadframe 12 and the semiconductor die 16 attached thereto. The enhancement layer 22 can be formed by treating the upper surface of the metal coating 20.

[0025] Such a molding compound can typically comprise a resin material such as an epoxy resin molding compound (EMC = epoxy molding compound).

[0026] As the metal coatings can be made of precious metals such as silver, which are an expensive material, the metal coating 20 can be in the form of a collection of spots, rather than a continuous layer / coating. In particular, the metal coating 20 can be applied in a dot-like fashion in order to limit the use of the (precious) metal plating.

[0027] For example, according to a treatment process designated as NEAP 4.0 (NEAP = Non-Etch Adhesion Promoter), the enhancement layer 22 can be an upper layer (3-10 nm) of silver oxide (AgOx) formed "on top" of the silver coating.

[0028] While promoting good adhesion with the packaging compound, the enhancement layer 22 was found to adversely affect the attachment process of the semiconductor die 16 onto the die pad area 14 of the leadframe 12.

[0029] Even if not wishing to be bound by any particular theory in this regard, the enhancement layer 22 can adversely affect the "wettability" of the solder attachment material to the leadframe material (copper coated with silver).

[0030] A composition of Pb 95% / Sn 5% or sometimes Pb with 1-2% Ag and Sn balancer can be an example of such a solder attachment material.

[0031] As Figure 2 And Figure 3 illustratively represented in Figs. 1 and 2, one or more embodiments can contemplate selectively removing the enhancement layer 22 at the area of the die pad area 14 to which the semiconductor die 16 is attached.

[0032] The wording "at" is intended to emphasize the fact that the selective removal of the enhancement layer 22 does not necessarily involve the entire die pad area to which the semiconductor die 16 is attached. However, an increase in the area where (solder) attachment can occur that is not adversely affected by the enhancement layer is found to be beneficial.

[0033] It is found that Figure 2 And Figure 3 laser beam ablation by laser L in Figs. 1 and 2 is effective in performing such selective removal of the enhancement layer, with the ability to restore the original wettability of the underlying metal coating 20 (e.g. "pure" silver, as in the case exemplified in Fig. 2). Figure 3

[0034] It is found that the selective removal of the enhancement layer 22 by laser beam ablation results in a "cleaning" of the surface of the leadframe from which the enhancement layer is removed (e.g. the surface of the silver coating in Fig. 2), with the effect that this surface is melted and / or roughened. Figure 3

[0035] This is found to be beneficial in (further) promoting adhesion of the solder material to the leadframe as well as promoting anchoring of the semiconductor die 16 thereon, with a reduced delamination risk.

[0036] Again, without wishing to be bound by any particular theory in this regard, such surface melting / roughening can result in an increased contact surface of the solder material with the leadframe, resulting in a synergistic increased wettability / increased contact surface resulting from the (selective) removal of the enhancement layer.

[0037] Experiments performed by the applicant have shown that laser beam radiation at a wavelength of approximately 1064 nm, as generated by a YAG laser, with a specific power of 100 Watt @ 1 MHz (pulsed with a pulse duration of 15 pSec) can provide for a robust solder die attachment to silver-coated leadframes, while the AgOx enhancement layer left on the part of the leadframe that is eventually in contact with the package molding compound promotes satisfactory package delamination performance as desired.

[0038] As exemplified herein, a method of manufacturing a semiconductor device (e.g. 10) can comprise:

[0039] - providing a leadframe (e.g. 12) having a die pad area (e.g. 14), ​​

[0040] - attaching at least one semiconductor die (e.g., 16) to the die pad area via a soft solder die attach material,

[0041] - forming a device package (e.g., 18) by molding a package material onto the at least one semiconductor die attached to the die pad area on the leadframe,

[0042] wherein the method comprises:

[0043] - providing an enhancement layer (e.g., 22) that counters delamination of the device package onto the leadframe,

[0044] - removing (e.g., L) the enhancement layer from at least a portion of the die pad area, and

[0045] - attaching the at least one semiconductor die to the die pad area via a soft solder die attach material provided at where the enhancement layer has been removed.

[0046] The method as exemplified herein can comprise removing the enhancement layer from the die pad area via laser ablation.

[0047] In the method as exemplified herein, the enhancement layer can comprise a treated silver, optionally a non-etch adhesion promoter (NEAP) treatment.

[0048] The method as exemplified herein can comprise:

[0049] - forming the leadframe of a first metallic material,

[0050] - forming a layer of a second metallic material on the leadframe, and

[0051] - treating a surface of the second metallic material opposite the first metallic material to provide the enhancement layer.

[0052] In the method as exemplified herein, the first metallic material can comprise copper.

[0053] In the method as exemplified herein, the second material can comprise silver.

[0054] The semiconductor device (e.g., 10) as exemplified herein can comprise:

[0055] - a leadframe (e.g., 12) having a die pad area (e.g., 14),

[0056] - at least one semiconductor die (e.g., 16) attached to the die pad area (14) via a soft solder die attach material,

[0057] - a device package (e.g., 18) of encapsulation material molded onto at least one semiconductor die attached to the die pad area on a leadframe,

[0058] wherein:

[0059] - a reinforcement layer (e.g., 22) is provided on the leadframe, the reinforcement layer countering delamination of the device package, wherein the die pad area of the leadframe is at least partially free (e.g., L) of the reinforcement layer, and

[0060] - the at least one semiconductor die is attached to the die pad area via a soft solder die attach material, the soft solder die attach material being provided at the die pad area of the leadframe that is free of the reinforcement layer.

[0061] In devices as exemplified herein, the die pad area of the leadframe at the location free of the reinforcement layer can have a rough surface that is wetted by the soft solder die attach material.

[0062] In devices as exemplified herein:

[0063] - the leadframe can comprise a first metallic material (optionally, copper) having a layer of a second metallic material (optionally, silver) formed thereon, and

[0064] - the reinforcement layer can comprise a treated (optionally, non-etch adhesion promoter or NEAP treated) layer of the second metallic material.

[0065] Details and embodiments can vary, even significantly, with respect to what is described by way of example only, without departing from the scope of protection.

[0066] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above detailed description. The terms used in the following claims should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the claims should be construed more broadly, in accordance with the principles of patent law. Thus, the claims are not limited to the embodiments disclosed in the specification and the claims.

Claims

1. A method for manufacturing a semiconductor device, the method comprising: A reinforcement layer is formed in the die pad area of ​​the leadframe and on the lead, the reinforcement layer being configured to counteract device package layering, and the lead is surrounding the die pad area, wherein the reinforcement layer comprises treated silver. Remove all of the reinforcement layer from the bare die pad area, leaving the reinforcement layer on the lead; After removing all the reinforcement layers from the die pad area, the semiconductor die is attached to the die pad area via a soft solder die attachment material; as well as A device package is formed by molding packaging material onto the semiconductor die attached to the die pad area of ​​the lead frame.

2. The method of claim 1, wherein removing the reinforcement layer from the bare die pad region comprises ablating the reinforcement layer with a laser beam.

3. The method of claim 2, wherein removing the laser beam that ablates the reinforcement layer further includes roughening the surface of the bare die pad region.

4. The method according to claim 1, wherein The lead frame is made of a first metallic material; and Providing the reinforcement layer to the die pad region of the lead frame and the lead includes: A layer of a second metal material is formed on the die pad region of the lead frame and on the lead, the layer of the second metal material having a first side facing the lead frame and a second side opposite to the first side; and The surface of the second side of the second metal material is processed.

5. The method of claim 4, wherein the first metallic material comprises copper.

6. The method according to claim 1, further comprising: Forming the reinforcement layer on the bare die pad region of the leadframe also includes forming the reinforcement layer on a metal coating on the leadframe.

7. A semiconductor device, comprising: A leadframe having a die pad region and leads around the die pad region, the leadframe having a first surface on the die pad region and a plurality of second surfaces on the leads. A reinforcement layer on the second surface of the lead on the lead frame, the reinforcement layer including an opening on the entire first surface exposing the die pad area, the reinforcement layer being configured to counteract device package layering, wherein the reinforcement layer includes treated silver; A semiconductor die is coupled to the first surface of the die pad region via a soft solder die attachment material; as well as The packaging material is molded onto the semiconductor die, which is attached to the die pad area of ​​the lead frame.

8. The semiconductor device of claim 7, wherein the die pad region of the lead frame has a rough surface wetted by the solder die attachment material.

9. The semiconductor device according to claim 7, wherein: The lead frame includes a first metallic material; and A second metallic material layer, wherein the reinforcing layer comprises a treated layer of the second metallic material.

10. The semiconductor device according to claim 9, wherein: The first metallic material is copper; and The second metallic material is silver.

11. The semiconductor device of claim 7, further comprising the enhancement layer disposed on a plurality of leads of the lead frame.

12. The semiconductor device of claim 7, further comprising a metal coating, wherein the metal coating includes the first surface of the die pad region, the metal coating is located in the die pad region, and the metal coating is located between the lead frame and the reinforcement layer.

13. A method comprising: A reinforcement layer is formed on the bare die pad area and on the lead frame leads, the reinforcement layer being configured to offset device package layering, wherein the reinforcement layer comprises treated silver; The reinforcement layer is ablated by laser to remove all of the reinforcement layer from the bare die pad area, while the reinforcement layer remains on the lead; as well as After laser ablation of the enhancement layer, the semiconductor die is attached to the die pad area via a soft solder die attachment material.

14. The method of claim 13, wherein The lead frame is made of a first metallic material; and Forming the reinforcement layer: A layer of a second metal material is formed on the die pad region of the lead frame and on the lead, the layer of the second metal material having a first side facing the lead frame and a second side opposite to the first side; and The surface of the second side of the second metal material is processed.

15. The method of claim 14, wherein the first metallic material comprises copper.

16. The method of claim 13, wherein laser ablation of the reinforcement layer to remove all of the reinforcement layer from the bare die pad region further comprises: Roughen the surface of the bare die pad area.

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