DIRECT SELECTIVE ADHESIVE PLATING

Abstract

A method of forming an encapsulated semiconductor device, comprising: Providing a lead frame strip (100) having a plurality of unit lead frames (106), each of the unit lead frames (106) having a central opening (130) and a plurality of leads (112) extending away from the central opening (130) with inner portions forming wire bond locations; selectively plating an adhesion promoter plating material (120) onto a first unit leadframe (106) within a package outline area (116) of first portions of the leads (112); Forming a cavity package outline (134) of electrically insulating encapsulant material on the first portions of the leads (112) such that the central opening (130) is enclosed by a cavity (136) formed by outer sidewalls of the encapsulant material; the method comprising: after selectively plating the adhesion promoter plating material (120) and after forming the cavity package outline (134), removing portions of the adhesion promoter plating material (120) that formed on the wire bond sites during formation of the adhesion promoter plating material (120).

Description

FIELD OF INVENTION

[0001] The present application relates to semiconductor encapsulation and, more particularly, to processes for increasing the adhesion between the conductive surface of a lead frame and the electrically insulating encapsulation material. GENERAL STATE OF THE ART

[0002] Integrated circuit devices such as semiconductor chips are typically encapsulated using a lead frame and an encapsulant material such as a molding compound. For example, one or more semiconductor chips may be physically attached to and electrically connected to a lead frame. The encapsulant material is formed around the semiconductor chip and the electrical connections. The encapsulant protects the semiconductor chip and the electrical connections from damaging environmental conditions such as humidity, temperature, foreign matter, etc. The leads of the lead frame are all externally accessible from outside the encapsulant and, in some cases, protrude from the encapsulant. These outer portions of the leads provide external electrical connections that allow the encapsulated device to be electrically connected to a printed circuit board, for example.

[0003] Many semiconductor processing technologies utilize leadframe strips to simultaneously package a number of semiconductor devices. A leadframe strip contains a number of unit leadframes continuously repeated on a lead sheet, with openings in the sheet defining the features of the unit leadframes. Each unit leadframe provides the lead structure for a single packaged device. One or more semiconductor dies can be attached to and electrically connected to each unit leadframe. Finally, the unit leadframes are singulated from each other to form individual packaged devices. The encapsulant can be formed on the leadframe before or after the unit leadframes are singulated.

[0004] In semiconductor packaging, delamination is a common problem, where the encapsulation material separates from the leadframe due to poor adhesion between the two. This can pose an unacceptable risk of moisture and foreign matter ingress into the package and can result in a number of parts being rejected after inspection.

[0005] One technique for addressing the adhesion problem involves applying an adhesion promoter to the lead frame prior to forming the encapsulant on the lead frame. However, effective adhesion promoters are typically non-conductive or at least interfere with conductive connections. Therefore, if the adhesion promoter is not removed from certain areas of the lead frame prior to wire bonding, there is a significant opportunity for wire bond failure. Known techniques for removing adhesion promoters from certain areas of the lead frame require multiple process steps that are expensive and difficult to calibrate.

[0006] The document US 5 540 378 A describes a method for forming an encapsulated semiconductor device comprising providing a lead frame, selectively plating an adhesion promoter material onto the lead frame, and forming a cavity package outline from electrically insulating encapsulation material.

[0007] The document JP 2007 - 123 571 A describes a method for manufacturing a semiconductor device, which additionally shows the plating of wire bonding locations exposed by the electrically insulating encapsulation material. BRIEF DESCRIPTION OF THE INVENTION

[0008] A method for forming an encapsulated semiconductor device having the features of claim 1 is disclosed.

[0009] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description and examining the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The elements of the drawings are not necessarily to scale relative to one another. Like reference numerals indicate corresponding similar parts. The features of the various illustrated embodiments may be combined, provided they are not mutually exclusive. Embodiments are illustrated in the drawings and set forth in detail in the description that follows. Fig. 1, which the Fig. 1A and Fig. 1B illustrates a leadframe strip that can be selectively plated, according to one embodiment. Fig. 1A shows a top side of the lead frame strip, and Fig. 1B shows the bottom side of the lead frame strip. Fig. 2, which the Fig. 2A and Fig. 2B illustrates a non-inventive mask provided over the leadframe strip, according to one embodiment. Fig. 2A shows a top side of the lead frame strip, and Fig. Figure 2B shows the bottom side of the lead frame strip. Fig. 3, which the Fig. 3A and Fig. 3B illustrates the non-inventive leadframe strip after adhesion promoter plating material has been selectively formed within openings of the mask, according to one embodiment. Fig. 3A shows a top side of the lead frame strip, and Fig. 3B shows the bottom side of the lead frame strip. Fig. 4 illustrates a top side of the non-inventive leadframe strip after the mask has been removed, according to one embodiment. Fig. 5 illustrates a top surface of a leadframe strip not according to the invention that has been processed by a chemical treatment process, according to one embodiment. Fig. 6 illustrates a top surface of a lead frame strip not according to the invention that has been processed by a laser cleaning process, according to one embodiment. Fig. 7 illustrates a top surface of a leadframe strip not according to the invention, with a wire-bondable layer formed on the wire bond pads of the leadframe, according to one embodiment. Fig. 8 illustrates a top surface of a lead frame strip not according to the invention, with a corrosion resistance coating that can be used to prevent the adhesion promoter plating material from forming at selected locations, according to one embodiment. Fig. 9 illustrates a top surface of a lead frame strip not according to the invention, with a pre-masking tape that can be used to prevent the adhesion promoter plating material from forming at selected locations, according to one embodiment. Fig. 10, which the Fig. 10A and Fig. 10B illustrates another configuration of a lead frame strip that can be selectively plated, according to one embodiment. Fig. 10A shows a top side of the lead frame strip, and Fig. Figure 10B shows a cross-sectional view of the lead frame strip. Fig. 11, which the Fig. 11A and Fig. 11B illustrates the lead frame strip of Fig. 10, after an adhesion promoter plating material has been selectively formed. Fig. 11A shows a top side of the lead frame strip, and Fig. Figure 11B shows a cross-sectional view of the lead frame strip. Fig. 12 illustrates a top surface of a leadframe strip with a molded package outline formed on the leadframe strip and with a wirebondable layer formed on the leadframe strip within the molded package outline, according to one embodiment. DETAILED DESCRIPTION

[0011] Embodiments of a method for forming an encapsulated semiconductor device are described herein. According to the method, a leadframe strip having a plurality of unit leadframes is provided. An adhesion promoter plating material is selectively deposited within a package perimeter area of ​​the unit leadframes. This process is a single-pass direct deposition process. For example, according to one embodiment, the unit leadframes are masked, and the adhesion promoter plating material is formed only in regions exposed to the mask.

[0012] The inventors have discovered that there are many advantages to a direct selective adhesion plating process compared to conventional techniques, which may include the non-selective plating of an adhesion promoter followed by an etching process, for example. However, with a direct selective adhesion plating process, the possibility exists that a small amount of the adhesion promoter may penetrate into the wire bond sites. The embodiments described herein address this problem by performing one or more processing steps on the wire bond sites in the leadframe strip before or after (or both before and after) the selective plating of the adhesion promoter. For example, the wire bond sites may be chemically treated and / or spot-plated with a wire-bondable layer (e.g., silver).These processing steps ensure that the wire bond sites are essentially free of the bonding agent plating material prior to wire bonding. Thus, the processing steps allow the leadframe strip to be plated using a direct selective bond plating process without the bonding agent plating material interfering with the formation of wire bonds.

[0013] With reference to Fig. 1, a top view of a lead frame strip 100 is shown, according to one embodiment. The top side 102 (i.e., the die attach side) of the lead frame strip 100 is shown in Fig. 1A, and the bottom side 104 of the lead frame strip 100 is shown in Fig. 1B. The lead frame strip 100 includes a plurality of unit lead frames 106, two of which are Fig. 1. For illustrative purposes, a first unit leadframe 106 will be discussed. Those of ordinary skill in the art will understand that the first unit leadframe 106 may be replicated multiple times in the leadframe strip 100 (e.g., dozens, hundreds of times, etc.), and that the configurations and processing steps discussed with reference to the first unit leadframe 106 are universally applicable to any of the other unit leadframes 106 in the leadframe strip 100.

[0014] The leadframe strip 100 may be formed from a film layer of electrically conductive material (e.g., copper, aluminum, and the like). Openings 108 are formed in the sheet, defining the features of the unit leadframes 106. The openings 108 may be formed, for example, by stamping or etching.

[0015] The first unit leadframe 106 includes a die paddle 110 and a plurality of leads 112 extending from the die paddle 110. A peripheral ring 114 separates inner portions of the leads 112 from outer portions of the leads 112. The peripheral ring 114 is an inner ring of the first unit leadframe 106 that surrounds the die paddle 110. The inner portions of the leads 112 are spaced closest to the die paddle 110, and the outer portions of the leads 112 are spaced farther away from the die paddle 110 on an opposite side of the peripheral ring 114 than the inner portions of the leads 112. The die paddle 110 may be connected to one of the leads 112 to connect the die paddle 110 so that the die paddle can be connected to a reference potential in the completed device.In a line trimming step, portions of the peripheral ring 114 that interconnect the lines 112 are removed so that the lines 112 are electrically distinct from each other. The first unit leadframe 106 may further include support legs 115 that physically support the die paddle 110 after the lines 112 have been trimmed.

[0016] A package outline region 116 represents where a protective encapsulation material, such as a molding compound, is formed on the first unit leadframe 106. The package outline region 116 surrounds the die paddle 110 and the inner portions of the leads 112. The outer portions of the leads 112 are at least partially located outside the package outline region 116 and thus protrude from the encapsulation material to provide electrical connections of the encapsulated device.

[0017] Fig. 1A further illustrates wire bonds 118 disposed within the package perimeter 116. Wire bonds (i.e., a conductive bond wire, ribbons, etc.) may be used to form an electrical bond between the semiconductor device(s) mounted on the die paddle 110 and the leads 112. The wire bonds 118 represent locations where the wire bonds connect to the leads 112 of the packaged device. The wire bonds 118 are disposed within the package perimeter 116 and spaced from the peripheral ring 114. That is, the wire bonds 118 do not intersect the package perimeter 116. Rather, the wire bonds 118 are disposed only on portions of the inner portions of the leads 112 that are closest to the die paddle 110.Optionally, the lines 112 may be enlarged locally at the wire bond sites 118 relative to the area of ​​the portions of the lines 112 that extend between the wire bond sites 118 and the peripheral ring 114.

[0018] With reference to the Fig. 2-3 illustrates a process for selectively forming an adhesion promoter plating material 120 within the package outline area 116 of the first unit leadframe 106 according to one embodiment. The top surface 102 of the leadframe strip 100 is shown in Fig. 2A, and the bottom side 104 of the lead frame strip 100 is in Fig. 2B. This process is a single-pass process whereby the adhesion promoter plating material 120 is applied directly to preselected portions of the leadframe. According to the method, a mask 122 is provided over the first unit leadframe 106. The mask 122 includes one or more openings 124 that at least partially expose preselected regions of the first unit leadframe 106 within the package outline area 116. The mask 122 covers preselected regions that are preferably free of (i.e., not covered by) the adhesion promoter plating material 120. The geometry of the mask 122 in Fig. 2A is merely an example, and in general, any mask geometry that is technically feasible may be used to define preselected regions of the leadframe strip 100 that should contain or be free of the adhesion promoter plating material 120.

[0019] With reference to Fig. 3, the adhesion promoter plating material 120 has been selectively formed on the lead frame strip 100. The top side 102 of the lead frame strip 100 is in Fig. 3A, and the bottom side 104 of the lead frame strip 100 is shown in Fig. 3B. Exposed portions of the leadframe strip 100 are plated with the adhesion promoter plating material 120, and the mask 122 nominally prevents the formation of the adhesion promoter plating material 120 in any of the covered areas.

[0020] The adhesion promoter plating material 120 may generally be any material that enhances the bond between the electrically insulating encapsulant material (i.e., a thermosetting plastic) and an electrically conductive material disposed on a surface of the leadframe (e.g., copper, aluminum, silver, etc.). According to one embodiment, the adhesion promoter plating material 120 is a zinc-based compound. For example, the adhesion promoter plating material 120 may be an alloy of zinc and chromium (e.g., ZnCr). Other suitable zinc-based alloys for the adhesion promoter plating material 120 include ZnMo or ZnV. According to one embodiment, the adhesion promoter plating material 120 is formed by an electrolytic plating process in which the leadframe strip 100 is immersed in an electrofluid and acts as an anode with an applied current.In this embodiment, the mask 122 prevents the covered area from being plated with the adhesion promoter plating material 120.

[0021] With reference to Fig. 4 shows a top surface 102 of the leadframe strip 100 after removal of the mask 122. In the figure, transition regions 126 of the inner portions of the leads 112 have been circled. These transition regions 126 correspond to areas at or near the boundary between the adhesion promoter plating material 120 and the wire bond pads 118. Without further measures, the adhesion promoter plating material 120 may warp too close to the die paddle 110 to penetrate the wire bond pads 118 in the transition regions 126. That is, the transition regions 126 represent areas that should preferably be free of the adhesion promoter plating material 120, but in some cases are not. Many variables that are difficult or impossible to control contribute to the problem. For example, the smallest opening size of the mask 122 may be such that the adhesion promoter plating material 120 extends too far into the wire bond sites 118.Process variation also contributes to this effect. Furthermore, even with a properly sized and aligned mask 122, some adhesion promoter plating material may penetrate into the wire bond pads 118 after the plating process. Because the adhesion promoter plating material 120 is non-conductive, it may be difficult or impossible to form wire bonds at the wire bond pads 118 if too much of the adhesion promoter plating material 120 is present in the transition regions 126.

[0022] A variety of processing steps are disclosed herein to mitigate the phenomenon described above and to remove (or cover) the adhesion promoter plating material 120 that forms in the transition regions 126. According to these embodiments, the wire bond pads 118 in the first unit leadframe 106 are processed such that the wire bond pads 118 are substantially free of the adhesion promoter plating material 120 after selectively plating the adhesion promoter plating material 120. That is, the wire bond pads 118 are processed to prevent the adhesion promoter plating material 120 from advancing too far toward the die paddle 110 and creating an unacceptably high risk of wire bond failure.These processing steps may be performed on the leadframe strip 100 before selectively plating the adhesion promoter plating material 120, after selectively plating the adhesion promoter plating material 120, or before and after selectively plating the adhesion promoter plating material 120. Furthermore, any of the processing steps may be combined. The term "substantially free," as used herein, means that while trace amounts of the adhesion promoter plating material 120 may be present on the wire bond pads 118, the amount of adhesion promoter plating material 120 remains below a maximum threshold to ensure that a conductive connection (i.e., with wire bonds) can be effected at the wire bond pads 118.

[0023] With reference to Fig. 5, a top surface 102 of the lead frame strip 100 is shown after selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-4. In this embodiment, the leadframe strip 100 has been subjected to a chemical treatment process either before or after the selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-3. As a result, the transition regions 126 are substantially free of the adhesion promoter plating material 120.

[0024] According to one embodiment, a chemical treatment process is applied to the first unit leadframe 106 prior to selectively plating the first unit leadframe 106 with the adhesion promoter plating material 120. For example, the leadframe strip 100 may be immersed in a chemically reactive solution. Example chemically reactive solutions suitable for this process include a chemical immersion or corrosion inhibitor, such as an organosulfuric acid based on, for example, 2-thiobarbituric acid, triazole derivatives, such as benzatriazole and imidazoles, etc. Alternatively, a silane-based solution such as mercaptosilane, sodium metasilicate, tripolyphosphate, etc., may be used. This chemical treatment process prevents the adhesion promoter plating material 120 from forming on selected portions (e.g., the wire bond sites 118) of the inner portions of the leads 112.Thus, during the selective application of the adhesion promoter plating material 120, with reference to . Fig. 4, not into the wire bonding points 118.

[0025] In another embodiment, after selectively plating the adhesion promoter plating material 120, portions of the adhesion promoter plating material 120 that are formed at the wire bond sites 118 during the plating process are removed. This removal of the adhesion promoter plating may be accomplished, for example, through a chemical reaction process. For example, chemical cleaning solutions such as potassium hydroxide, ammonium acetate, potassium lactate, and acetone may be applied to the wire bond sites 118. This process may be selective or non-selective and may be an electrolytic or non-electrolytic process. For example, in a selective cleaning process, a mask may be used to remove only the adhesion promoter plating material 120 from preselected areas (e.g., the wire bond sites 118 or portions of the wire bond sites 118).Alternatively, in a non-selective cleaning process, the chemical cleaning solution may be exposed to the entire lead frame strip 100 for a predetermined duration to remove a portion of the adhesion promoter plating material 120.

[0026] With reference to Fig. 6, a top surface 102 of the lead frame strip 100 is shown after selective plating of the adhesion promoter plating material 120, as described above with reference to the Fig. 2-4. In this embodiment, the leadframe strip 100 has been subjected to selective laser cleaning in exit regions 127 surrounding the wire bond pads 118. This selective laser cleaning is performed after the selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-4. Various laser parameters are possible. Laser-selective cleaning can slightly reduce the thickness of the material beneath the adhesion promoter plating material 120 (e.g., silver), allowing the adhesion promoter plating material 120 to be completely removed. Removal of unwanted plating can be performed, for example, by laser machine programming. Laser cleaning can be applied to various metal surfaces (Cu, Ag, Ni, pre-plating layer stacks, etc.).

[0027] With reference to Fig. 7, a top surface 102 of the lead frame strip 100 is shown after selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-4. In this embodiment, the leadframe strip 100 has undergone a plating process, whereby any adhesion promoter plating material 120 present in the wire bond pads 118 is covered (e.g., plated) with a wire-bondable layer 128. The wire-bondable layer 128 may generally be any electrically conductive material suitable for forming wire connections thereon. According to one embodiment, the wire-bondable layer 128 is a layer of silver (Ag). Alternatively, the wire-bondable layer 128 may be formed from palladium (Pd), gold (Au), nickel (Ni), copper (Cu), and alloys thereof.

[0028] According to one embodiment, the wire-bondable layer 128 is formed using a so-called spot plating technique. According to this technique, the wire-bondable material (e.g., silver) is applied at preselected locations directly onto the first unit leadframe 106. As can be seen, the preselected locations are within the package perimeter area 116 and include the die paddle 110 and the wire bond portions of the leads 112. Any adhesion promoter that forms on or near the wire bond portions of the leads 112 will be covered by the wire-bondable layer 128. However, the spot plating is confined within a window so that it does not form near the package perimeter or the peripheral ring 114. Thus, in these areas, the adhesion promoter plating material 120 remains exposed and adheres to the encapsulation material formed thereon.The wire-bondable layer 128 may be formed before and after the application of the adhesion promoter plating material 120. For example, the wire-bondable layer 128 may first be deposited on the leadframe strip 100 prior to the steps described with reference to FIG. Fig. 2-3. A replating process may then be applied to form another wire-bondable layer 128.

[0029] With reference to Fig. 8, a top surface 102 of the lead frame strip 100 is shown prior to selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-4. According to the Fig. 8, the entire leadframe strip 100 is coated with a corrosion resistance coating 129 using pore blocking chemistry techniques including bisphenol, ether-based chemistry, benzothiazole, etc. The corrosion resistance coating 129 forms a hydrophobic layer on the entire top side 102, including the wire bond pads 118, as well as the bottom side 104 (in Fig. 8 (not shown). The corrosion resistance coating 129 may be used to block the formation of the adhesion promoter plating material 120 in any desired area, including the wire bond sites 118 and the transition regions 126. The adhesion promoter plating material 120 may not be deposited at these locations by immersion or a low current flow. However, the adhesion promoter plating material 120 may be selectively applied to other areas where it is preferentially present (e.g., the peripheral ring 114). The corrosion resistance coating 129 may be applied prior to the selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-4, and can remain on the wire bond pads 118 during wire bonding without disturbing the wire connections due to the minimal thickness of the corrosion resistance coating 129.

[0030] With reference to Fig. 9, a top surface 102 of the lead frame strip 100 is shown prior to selective plating of the adhesion promoter plating material 120, as described with reference to Fig. 2-3. According to these techniques, an additional masking step is performed before the masking step of Fig. 2 to provide additional coverage over the wire bond pads 118 and prevent the formation of the adhesion promoter plating material 120 in these areas. This additional masking step may involve applying a pre-taping process, whereby a tape 131 is applied to the leadframe strip 100. The tape 131 may be any commonly used tape for line stabilization, such as a polyethylene tape (PE tape) or a polyester tape (PET tape).

[0031] With reference to Fig. 10, a differently configured lead frame strip 100 is shown. The top side 102 (ie, the die attachment side) of the lead frame strip 100 is in Fig. 10A. Fig. 10B shows the lead frame strip 100 along the Fig. 10A. In this embodiment, the leadframe strip 100 is configured to be preformed with a package outline structure prior to singulation of the first unit leadframes 106.

[0032] The leadframe strip 100 may contain the same materials and may be formed according to the same techniques as the one described with reference to Fig. 1-9 described lead frame strip 100. The lead frame strip 100 is distinguished from the lead frame strip 100 of Fig. 1-9 are configured differently. First, there is no die paddle 110 in the lead frame strip 100 of Fig. 10. Instead, each of the unit leadframes 106 has a central opening 130. The unit leadframes 106 additionally include a plurality of leads 112 extending from the central opening 130. This configuration can be used for a sensor package structure in which the sensor component is placed over the central opening 130. The central opening 130 can provide access to the outside of the package so that the sensor component can measure an external environmental parameter.

[0033] Referring to the side profile view of Fig. 10B, it can be seen that the leadframe strip 100 may have a bent lead configuration. In particular, a raised portion 132 is provided in first portions of the leads 112. That is, the leads 112 do not extend along a single plane. Rather, the leads 112 include a vertical bend and a raised portion 132 spaced above outer portions of the leads 112. The raised portion 132 is closer to the central opening 130 than outer portions of the leads 112. In addition, the leads 112 may be bent downward at inner portions of the leads 112 located at the central opening 130.

[0034] With reference to Fig. 11, an adhesion promoter plating material 120 is selectively applied within a package outline area 116 of the first unit leadframe 106. The top side 102 (ie, the die attach side) of the leadframe strip 100 is in Fig. 11A. Fig. 11B shows the lead frame strip 100 along the Fig. 11A. The adhesion promoter plating material 120 can be applied to the lead frame strip of Fig. 1 be trained in a process that is similar to that described in Fig. 2-4. For example, the adhesion promoter plating material 120 may be selectively plated by providing a mask 122 over the first unit leadframe 106 and forming the adhesion promoter plating material 120 in one or more openings of the mask 122 (e.g., by electroplating). According to one embodiment, the adhesion promoter plating material 120 is selectively formed on the first portions of the leads 112 that include the raised portions 132, as shown in Fig. 11B.

[0035] With reference to Fig. 12, a cavity package outline 134 has been glued to the leadframe strip 100. The cavity package outline 134 may be a preformed structure that is glued to the leadframe strip 100, for example, using an epoxy. Alternatively, the cavity package outline 134 may be molded directly onto the leadframe strip 100. The cavity package outline 134 is formed on the first portions of the leads 112 such that the central opening 130 is enclosed by a cavity 136 formed by outer sidewalls of the encapsulation material. That is, the outer sidewalls of the cavity package outline 134 enclose and surround the central opening 130. The outer sidewalls of the cavity package outline 134 may be formed on the raised portions 132 of the leads 112.The adhesion promoter plating material 120 is provided at an interface between the lead frame and the electrically insulating encapsulant material.

[0036] The first unit leadframe 106 may be processed after forming the cavity package outline 134 to prevent the adhesion promoter plating material 120 from interfering with electrical connections between the first unit leadframe 106 and the components (e.g., sensor elements) mounted within the cavity 136. For example, the leadframe strip 100 may be processed before or after the selective plating process in a manner similar to that described with reference to Fig. 5. However, these steps may be omitted. Because the electrically insulating encapsulant is formed on the leadframe strip 100 during processing of the leadframe strip 100, the leadframe strip 100 may be subsequently processed to eliminate any potentially adverse effects of the adhesion promoter plating material 120 on the leads 112.

[0037] According to one embodiment, after the cavity package outline 134 has been formed on the leadframe strip 100, the first unit leadframe 106 is plated with a wire-bondable layer 128. The wire-bondable layer 128 may be a layer of silver (Ag) and may be formed according to the same techniques previously described with reference to Fig. 6. Therefore, any adhesion promoter plating material 120 on the leads 112 will not interfere with the electrical connections between the first unit leadframe 106 and the components mounted within the cavity 136.

[0038] The Fig.1-12 illustrate two possible embodiments of the first unit leadframe 106. However, the configuration of the first unit leadframe 106 may vary depending on the desired configuration of the finalized package design. For example, the number and dimensions of the leads 112 and the size of the die paddle 110 may vary. The first unit leadframe 106 may be formed along a single plane or may be formed along more than one plane. For example, the first unit leadframe 106 may be vertically offset from the peripheral ring 114. Additionally, the leads 112 may have one or more bends or otherwise include a non-planar geometry. In any event, the selective plating of the adhesion promoter plating material process and the wire bond processing techniques described herein may be applied to any of these designs.

[0039] The single-pass process offers numerous advantages over conventional techniques that require two-pass rework (e.g., a non-selective adhesion promoter step followed by selective adhesion promoter etching). A key advantage is cost reduction. This cost reduction can be attributed, at least in part, to the elimination of at least one mask (i.e., the mask required for selective adhesion promoter etching). Furthermore, carrier alignment and handling problems associated with conventional techniques are reduced due to the simplification of the process. Thus, yield can be improved.

[0040] Another advantage of the single-pass process compared to conventional techniques is that no thickness reduction of the conductive leadframe material is required. Conventional processes require over-etching the adhesion promoter to remove the material underlying the adhesion promoter. This is necessary to ensure that the adhesion promoter is completely removed from the wire-bondable layers. This thickness reduction of the conductive leadframe material can lead to a number of adverse effects. For example, mold burring may occur, and package singulation may be more difficult due to the non-planar nature of the leadframe. Thickness reduction is not necessary using the techniques described herein because the adhesion promoter is applied only in the areas where it is required.

[0041] Another advantage of the direct selective bond coat plating process described herein is an improvement in the shelf life of the direct selective bond coat plating material. According to conventional techniques, the package forming process should be performed within two weeks of the bond coat plating process. According to the direct selective bond coat plating process described here, the lead frame can be formed up to 12 months after the bond coat plating material is applied. Thus, the direct selective bond coat plating process described herein offers flexibility regarding prefabrication, shipping, and delivery.

[0042] Spatially relative terms such as "below," "underneath," "lower," "above," "upper," and the like are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass other orientations of the device in addition to various orientations than those described in the figures. Furthermore, terms such as "first," "second," and the like are also used to describe various elements, regions, sections, and so forth, and are also not intended to be limiting. Like terms refer to like elements throughout the description.

[0043] As used herein, the terms "with," "including," "comprising," and the like are open-ended terms that indicate the presence of stated elements or features but do not preclude additional elements or features. The articles "a," "an," and "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

Claims

[1] A method of forming an encapsulated semiconductor device, comprising: Providing a lead frame strip (100) having a plurality of unit lead frames (106), each of the unit lead frames (106) having a central opening (130) and a plurality of leads (112) extending away from the central opening (130) with inner portions forming wire bond locations; selectively plating an adhesion promoter plating material (120) onto a first unit leadframe (106) within a package outline area (116) of first portions of the leads (112); Forming a cavity package outline (134) of electrically insulating encapsulant material on the first portions of the leads (112) such that the central opening (130) is enclosed by a cavity (136) formed by outer sidewalls of the encapsulant material; the method comprising: after selectively plating the adhesion promoter plating material (120) and after forming the cavity package outline (134), removing portions of the adhesion promoter plating material (120) that formed on the wire bond sites during formation of the adhesion promoter plating material (120). [2] The method of claim 1, further comprising: after forming the cavity package outline (134), plating the wire bonding sites exposed by the electrically insulating encapsulant with a wire bondable layer (128). [3] The method of claim 1 or 2, wherein the first portions of the leads (112) include a raised portion (132), the raised portion (132) being closer to the central opening (130) than outer portions of the leads (112) and farther from the central opening (130) than the inner portions of the leads (112), and wherein the outer sidewalls of the encapsulating material are formed on the raised portions (132) of the leads (112). [4] The method of claim 3, wherein selectively plating the adhesion promoter plating material (120) comprises a single-pass plating process, the single-pass plating process comprising: Providing a mask (122) over the first unit leadframe (106), the mask (122) covering the outer portions of the leads (112) and including openings exposing the raised portions (132) of the leads (112); and Forming the adhesion promoter plating material (120) in the openings. [5] The method of claim 1, wherein removing portions of the adhesion promoter plating material (120) formed on the wire bond sites comprises applying a chemical cleaning solution to the wire bond sites, the chemical cleaning solution comprising at least one of the following: potassium hydroxide, ammonium acetate, potassium lactate, and acetone. [6] The method of claim 5, wherein applying the chemical cleaning solution comprises a selective cleaning process that exposes the wire bond sites to the chemical cleaning solution and protects adjacent areas from the chemical cleaning solution. [7] The method of any one of claims 1 to 6, wherein processing the wire bond sites comprises: after selectively plating the adhesion promoter plating material and after forming the cavity package outline (134), applying a laser cleaning process to the wire bond sites to remove any adhesion promoter plating material that oozes onto the wire bond sites. [8] The method of any one of claims 1 to 7, wherein processing the wire bond sites comprises: Before providing the mask over the first unit lead frame, applying a tape over the wire bond pads.

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