Power die package

Abstract

A power die package includes a leadframe having a flag stand with power leads on one side and signal leads on one or more other sides. A power die is attached to a bottom surface of the flag stand and electrically connected to the power leads with conductive epoxy. A control die is attached to a top surface of the flag stand and electrically connected to the signal leads with wire bonds. A molding compound is provided to encapsulate the dies, wire bonds, and proximal portions of the leads, while distal portions of the leads are exposed, forming a PQFN package.

Description

Technical Field

[0001] This invention relates to integrated circuit (IC) packaging, and more particularly to power die packaging. Background Technology

[0002] Figure 1 is a cross-sectional side view of a conventional power die package 10 assembled using a lead frame having a flag 12 and leads 14 surrounding the flag 12. A power die 16 is attached to the top surface of the flag 12 using lead-free die-attach adhesive 18, and a control die 20 is attached to the top surface of the power die 18 using an adhesive film 22. The power die 16 is electrically connected to the first set of leads 14 using thick aluminum bonding wires 24 (e.g., 15 mils in diameter), while the control die 20 is electrically connected to the second set of leads 14 using thin copper bonding wires 26 (e.g., 1.5 mils in diameter). The entire assembly is covered with a sealant 28. The sealant 28 is provided to protect dies 16 and 20, as well as the wire connections, from damage.

[0003] The power die 16 generates heat that must be dissipated, so the flag 12 is formed of a relatively thick copper sheet, and the die adhesive must have good thermal properties. These factors increase the overall cost of the package 10. Reducing the assembly cost of this type of power die package would be advantageous. Attached Figure Description

[0004] From the following detailed description, the appended claims, and the accompanying drawings, various aspects, features, and advantages of the invention will become fully apparent, in which the same reference numerals denote similar or identical elements. Some elements shown in the drawings may be enlarged and are therefore not drawn to scale in order to present the invention more clearly.

[0005] Figure 1 is an enlarged cross-sectional side view of a conventional power die package;

[0006] Figure 2 This is an enlarged cross-sectional side view of a power die package according to an embodiment of the present invention;

[0007] Figure 3 yes Figure 2 A flowchart of the assembly process of the power die package;

[0008] Figure 4A yes Figure 2 A top plan view of the lead frame of the power die package, and Figure 4B It is along Figure 4A The side view of line AA;

[0009] Figure 5A and 5B It is shown Figure 3Top and side views of the power die mounting step in the assembly process;

[0010] Figure 6A and 6B It is shown Figure 3 Top and side views of the control die attachment step in the assembly process;

[0011] Figure 7A and 7B It is shown Figure 3 Top plan view and cross-sectional side view of the wire joining step in the assembly process;

[0012] Figure 8 It is shown Figure 3 An enlarged cross-sectional side view of the molding steps in the assembly process; and

[0013] Figure 9A and 9B yes Figure 2 Top and bottom view diagrams of the power die package. Detailed Implementation

[0014] This document discloses detailed exemplary embodiments of the present invention. However, the specific structural and functional details disclosed herein are merely representative and are intended to describe exemplary embodiments of the invention. Embodiments of the invention can be implemented in many alternative forms and should not be construed as limited to the embodiments set forth herein. Furthermore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the invention.

[0015] As used herein, the singular forms “a,” “an,” and “the” also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the words “comprising,” “including,” “having,” “possessing,” “containing,” and / or “containing” indicate the presence of the stated feature, step, or component, but do not preclude the presence or addition of one or more other features, steps, or components. It should also be noted that in some alternative implementations, the indicated functions / behaviors may not appear in the order shown in the figures.

[0016] In one embodiment, the present invention provides a power die package including a lead frame, a control die, and a power die. The lead frame includes a flag base having a top or upper surface for receiving the control die and a bottom or lower surface for receiving the power die. The lead frame also has a plurality of power leads adjacent to and spaced apart from a first side of the flag base and a plurality of signal leads adjacent to and spaced apart from at least one other side of the flag base. The power leads have a proximal end near the flag base and a distal end spaced further away from the flag base. The control die has a back surface attached to the upper surface of the flag base and an active surface opposite the back surface, the active surface including a plurality of control die electrodes. A first set of control die electrodes is electrically connected to the plurality of signal leads via a first bonding wire. The power die has a first surface attached to the lower surface of the flag base. The power die has a plurality of power die electrodes, the plurality of power die electrodes including a first set of power die electrodes electrically connected to the plurality of power leads. In other embodiments, the second set of control die electrodes is connected to the second set of power die electrodes via a second bonding line, and the entire assembly is covered with a molding compound.

[0017] The present invention also provides a method for assembling a power die package, the method comprising providing a lead frame having a flag base having a top or upper surface for receiving a control die and a bottom or lower surface for receiving a power die. The lead frame further has a plurality of power leads adjacent to and spaced apart from a first side of the flag base and a plurality of signal leads adjacent to and spaced apart from at least one other side of the flag base. The power leads have a proximal end near the flag base and a distal end spaced further away from the flag base. The active side of the power die is attached to the lower surface of the flag base. The power die has a larger footprint than the flag base, such that a portion of the power die is suspended above the flag base, and the suspended portion of the power die has a plurality of power die electrodes, including a first set of power die electrodes in contact with and electrically communicating with the proximal ends of the power leads. The back side of the control die is attached to the upper surface of the flag base. The active side of the control die opposite the back side of the flag base includes a plurality of control die electrodes. The first set of control die electrodes is electrically connected to the plurality of signal leads via a first bonding line, and then the flag, the proximal end of the power lead, the signal lead, the control die, the power die, the electrical connection between the power lead and the first set of power die electrodes, and the first bonding line are wrapped with a molding compound, wherein the bottom surface of the power die is exposed.

[0018] This invention provides a lower-cost power die package than currently available packages because the lead frame is cheaper and does not require thick aluminum bonding wires. Furthermore, since the entire bottom surface of the power die is not attached to the flag holder, either a lower-cost die attach material can be used, or less of the more expensive die attach material is required, thus reducing the cost of attaching the power die to the flag holder. The package of this invention also has better thermal performance than conventional power die packages because the bottom surface of the power die is exposed.

[0019] Now refer to Figure 2 The image shows a cross-sectional side view of a power die package 100 according to an embodiment of the present invention. The power die package 100 includes a lead frame having a flag base 102 having a top or upper surface 104 for receiving a control die and a bottom or lower surface 106 for receiving a power die. The lead frame also has a plurality of power leads 108 adjacent to and spaced apart from a first side of the flag base 102 and a plurality of signal leads 110 adjacent to and spaced apart from at least one other side of the flag base 102. The power leads 108 have a proximal end 112 near the flag base 102 and a distal end 114 spaced further away from the flag base 102.

[0020] The control die 116 has a back surface attached to the upper surface 104 of the flag base 102 and an active surface opposite thereto, the active surface including a plurality of control die electrodes. A first set of control die electrodes is electrically connected to the plurality of signal leads 110. In the presently preferred embodiment, the first plurality of control die electrodes are connected to the signal leads 110 via a first bonding wire 118. The first bonding wire 118 may include wires of copper, gold, or other conductive metals, as known in the art, and is connected to the die electrodes and lead frame leads 110 using commercially available wire bonding equipment.

[0021] The power die 120 has a first surface or active surface attached to the lower surface 106 of the flag base 102. The power die 120 has a plurality of power die electrodes on its active surface, said plurality of power die electrodes including a first set of power die electrodes electrically connected to a plurality of power leads 108. More particularly, according to a presently preferred embodiment of the invention, the proximal end 112 of the power lead 108 is in direct contact with the first set of power die electrodes.

[0022] The control die 116 is attached to the upper surface 104 of the flag base 102 with die attachment material 122, such as die-attachment epoxy resin or die-attachment adhesive tape, both of which are known in the art and commercially available. The power die 120 is attached to the lower surface 106 of the flag base 102 with conductive epoxy resin 124. The proximal end 112 of the power lead 108 is also connected to the first set of power die electrodes with conductive epoxy resin 126. The conductive epoxy resins 124 and 126 preferably comprise the same material. The die attachment material 122 can be conductive or non-conductive, while the epoxy resins 124 and 126 are conductive epoxy resins. Suitable conductive and non-conductive epoxy resins are known to those skilled in the art and are readily available on the market.

[0023] from Figure 2 As can be seen, the distal ends 114 of the signal lead 110 and the power lead 108 are located in the first plane AA, while the proximal end 112 of the power lead 108 and the flag seat 102 are located in the second plane BB. The second plane BB is parallel to and spaced apart from the first plane AA, such that the proximal end 112 of the power lead 108 is positioned on top of the first set of power die electrodes and is in electrical contact with it.

[0024] exist Figure 2 It can also be seen that the power die 120 has a larger footprint than the flag base 102, such that a portion of the power die 120, including the first set of power die electrodes, is suspended above the flag base 102. Then, the proximal end 112 of the power lead 108 can contact the first set of power die electrodes, but remains spaced apart from the flag base 102. Within the gap between the flag base 102 and the proximal end 112 of the power lead 108, the surface of the power die 120 is exposed, and a second set of power die electrodes is located within this exposed gap.

[0025] The control chip 116 attached to the upper surface 104 of the flag base 102 preferably has a smaller footprint than the flag base 102, such as... Figure 2 As shown. Although Figure 2 It is not necessarily drawn to scale, but it shows that in this preferred embodiment, the control die 116 is smaller than the power die 120 and the flag 102. The control die 116 also has a second set of electrodes electrically connected to the second set of power die electrodes via a second bonding line 128.

[0026] Molding compound 130 encapsulates the flag base 102, the proximal end 112 of the power lead 108, the signal lead 110, the control die 116, the power die 120, and the first and second bonding wires 118 and 128. Molding compound 130 protects dies 116 and 120, bonding wires 118 and 128, and wire connections from damage. Molding compound 130 also defines a package. The distal end 114 of the power lead 108, the side and bottom surfaces of the signal lead 110, and the bottom surface of the power die 120 are exposed. The exposed portions of the power lead 108 and the signal lead 110 allow for external electrical connections to the power die package 100.

[0027] In one embodiment, a metal coating 132 (such as a solder layer) is formed on the exposed bottom surface of the power die 120. The purpose of the metal coating 132 is to prevent mechanical damage to the bottom of the power die during device-level electrical testing and handling prior to surface mounting.

[0028] The lead frame can be formed of copper or other conductive metals known in the art and can be provided in strip or array form. The lead frame, or only selected portions thereof (such as the outer lead area of ​​the lead), can be coated or electroplated with another metal or alloy to inhibit corrosion when the lead frame is exposed to the external environment. The lead frame can be formed by cutting, stamping, and / or etching copper sheets or foils. In one embodiment, the die receiving area includes a die liner, i.e., a solid copper element on which dies 116 and 120 are mounted. In some embodiments, the die liner can be made relatively thick so that it can act as a heat sink, absorbing heat generated by dies 116 and 120.

[0029] The control die 116 may include digital circuitry for receiving signals from and supplying signals to other integrated circuit chips, while the power die 120 may include analog circuitry, such as a power MOSFET. In one embodiment, the power die package 100 may include an integrated circuit capable of controlling, for example, automotive headlights, such as the NXP eSwitch (eXtreme Switch), available from NXP BV in the Netherlands, which includes features such as a 16-bit SPI with daisy-chain capability, a PWM module with an external or internal clock, intelligent overcurrent shutdown, overtemperature protection, automatic retry of most protection measures, fail-safe mode, open-circuit load protection for bulbs or LEDs, battery short-circuit detection, and analog current and temperature feedback.

[0030] Figure 3 It is used for assembly Figure 2 The flowchart 150 shows the method of encapsulation 10, and Figure 4A-8 The encapsulation 10 is shown at different stages of the assembly process.

[0031] In preparatory step 152, wafer dicing is performed to provide multiple power dies and multiple control dies. In the presently preferred embodiment, the power dies and control dies are manufactured on separate wafers, but the dicing step can be performed on both wafers in the same assembly site. Additionally, in step 152, as shown... Figure 4A and 4B The lead frame shown is like the one indicated by 170. More specifically, Figure 4A and 4B A portion of a leadframe 170 according to an embodiment of the present invention is shown. The leadframe 170 is part of a leadframe array, allowing multiple packages to be assembled simultaneously. The leadframe 170 includes a flag base 172, a plurality of power leads 174, and a plurality of signal leads 176. The flag base 172 has an upper surface 178 for receiving a control die and a lower surface 180 for receiving a power die. The power leads 174 are located adjacent to and spaced apart from a first side 182 of the flag base 172, while the signal leads 176 are adjacent to and spaced apart from at least one other side of the flag base 172. In the illustrated embodiment, the signal leads 176 are arranged around the remaining three sides of the flag base 172. The power leads 174 have a proximal end 184 close to the flag base 172 and a distal end 186 spaced further away from the flag base 172. Figure 4B As can be seen, the proximal end 184 of the flag base 172 and the power lead 174 is located in a first plane, and the distal end 186 of the signal lead 176 and the power lead 174 is located in a second plane, which is spaced apart from and parallel to the first plane. The lead frame 170 can be formed on-site or by a lead frame supplier at point a, and as discussed above, the lead frame can be plated with one or more metals or alloys to prevent corrosion.

[0032] In step 154, the power die is attached to the lead frame. In the currently preferred embodiment, the lead frame 170 is flipped over so that the lower surface 180 faces upward, as shown below. Figure 4A and 4B As shown, conductive epoxy resin 188 is disposed on the lower surface 180 of the flag base 172 and the proximal end 184 of the power lead 174. The conductive epoxy resin 188 may be dispensed onto the flag base 172 and the power lead 174 in an X-pattern or as a drop or blob or smear (not a particular shape).

[0033] Figure 5A and 5BThe active surface of a power die 190 attached to the lower or bottom surface of a flag holder 172 is shown. The power die 190 has a larger footprint than the flag holder 172, such that a portion of the power die 190 is suspended above the flag holder 172, and the portion of the power die 190 suspended above the flag holder 172 has a plurality of power die electrodes including a first set of power die electrodes that are in contact with and electrically communicate with the proximal end 184 of the power lead 174. Thus, the power die 190 spans the gap between the flag holder 172 and the power lead 174, and is positioned on both the flag holder 172 and the power lead 174. (Refer to...) Figure 5B Although the right-hand side of the figure shows that the side of the flag holder 172 and the side of the power die 190 are not aligned, misalignment of the flag holder 172 and the power die is not required. For example, if the flag holder 172 is not too wide so that its side aligns with the side of the power die 190, the lead frame will use less metal.

[0034] In step 156 ( Figure 3 After attaching the power die 190, tape 192 is placed on the distal end 186 of the power lead 174, the power die 190, and the signal lead 176, as shown. Figure 6B As shown. The component is then flipped over, and in step 158, the control die 194 is attached. Figure 6A and 6B As shown, the control die 194 is attached to the upper surface 178 of the flag holder 172 with a die-attachment film or die-attachment epoxy resin 196. The control die 194 is attached with its active side facing upwards, making the plurality of first sets of control die electrodes 198 and the plurality of second sets of control die electrodes 200 accessible. The power die 190 also has a plurality of second electrodes 202 located on the power die 190 and visible within the gap between the flag holder 172 and the power lead 174.

[0035] In step 160, a first electrical connection is made between the first set of control die electrodes 198 and the signal lead 176, and a second electrical connection is made between the second set of control die electrodes 200 and the power die 190. More specifically, as Figure 7A and 7B As shown, the first set of control die electrodes 198 is electrically connected to a plurality of signal leads 176 via a first bonding line 204, and the second set of control die electrodes 200 is electrically connected to a second set of power die electrodes 202 via a second bonding line 206. The first and second bonding lines 204 and 206 may include the same wire type, for example, 1.5 mil copper wire.

[0036] After online joining, in step 162 ( Figure 3Molding compound 208 is formed on portions of dies 190 and 194, first and second bonding wires 204 and 206, and power leads 174 and signal leads 176, as shown. Figure 8 The molding compound 208 can be formed on the component using a "molded array packaging" or MAP process known in the art. After molding, the bottom surface of the power die 190 is exposed, as are portions of the signal lead 176 and the distal end 186 of the power lead 174. Furthermore, the adhesive tape 192 is removed after molding.

[0037] Figure 9A and 9B These are top and bottom view diagrams of the power device 212 assembled according to the above method. In the top view ( Figure 9A In the top view, portions of the molded compound 208, power lead 174, and signal lead 176 are visible, while in the bottom view ( Figure 9B In the diagram, more power leads 174 and signal leads 176 are visible. The bottom surface of the power die 190 is also exposed, as shown in the reference above. Figure 8 As indicated. However, in some embodiments, the exposed bottom surface of the power die 190 is coated with a conductive material (such as gold or solder). Figure 9B In the middle, the bottom surface of the power die 190 is coated with gold 210. When needed, cutting and shaping operations can be performed to complete the formation of a Quad Flag No-leads (QFN) package.

[0038] It should now be clear that the present invention includes a lead frame for a PQFN type package. PQFN offers lower parts and assembly costs for power devices because the lead frame can be formed using a stamping process, which is less expensive than etching processes. Furthermore, the flag and leads can have the same thickness, so the cost is not increased by having a more complex lead frame structure. The power die is directly connected to the power leads, so a separate wire bonding process using expensive thick aluminum wire is not required. Both dies are equally suited to the opposite sides of the lead frame flag.

[0039] The reference to "an embodiment" or "an embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, and individual or alternative embodiments are not necessarily mutually exclusive with other embodiments. The same applies to the word "implementation".

[0040] For the purposes of this description, the terms “coupled,” “coupled,” “coupled,” “connected,” “positive connection,” or “connected” refer to any form known in or to be developed in the art where energy is allowed to be transferred between two or more elements, and the involvement of one or more additional elements is anticipated, though not necessary. The terms “direct coupling,” “indirect coupling,” etc., mean that the connected elements are either in contact or connected via a conductor for energy transfer.

Claims

1. A power die package, comprising: A lead frame having a flag seat including an upper surface for receiving a control die and a lower surface for receiving a power die, a plurality of power leads adjacent to and spaced apart from a first side of the flag seat, and a plurality of signal leads adjacent to and spaced apart from at least one other side of the flag seat, wherein the plurality of power leads and the plurality of signal leads have the same thickness, and the power leads have a proximal end near the flag seat and a distal end spaced further away from the flag seat; The control die has a back surface attached to the upper surface of the flag base and an active surface opposite the back surface, comprising a plurality of control die electrodes, wherein a first set of control die electrodes is electrically connected to the plurality of signal leads. as well as A power die has a first surface attached to the lower surface of the flag base, wherein the power die has a plurality of power die electrodes, the plurality of power die electrodes including a first set of power die electrodes electrically connected to the plurality of power leads; wherein: The first set of control die electrodes is electrically connected to the plurality of signal leads via a first bonding wire; and The power die package also includes a second set of control die electrodes that are different from the first set of control die electrodes. The second set of control die electrodes is electrically connected to the second set of power die electrodes that are different from the first set of power die electrodes via a second bonding line. The power die has a larger footprint than the flag base, such that a portion of the power die including the first set of power die electrodes is suspended on the flag base; and the first set of power die electrodes is in direct contact with the plurality of power leads.

2. The power die package according to claim 1, wherein: The first set of power die electrodes are attached to the plurality of power leads with conductive epoxy resin.

3. The power die package of claim 1, wherein the signal lead and the distal end of the power lead are located in a first plane, and the proximal end of the power lead and the flag are located in a second plane, wherein the second plane is parallel to and spaced apart from the first plane, such that the proximal end of the power lead is disposed on top of and in electrical contact with the first set of power die electrodes.

4. The power die package according to claim 1, wherein: The active surface of the power die is attached to the lower surface of the flag base with conductive epoxy resin, and the proximal end of the power lead is also attached to the first set of power die electrodes with conductive epoxy resin. The control core is attached to the flag base with a core-attach adhesive tape.

5. The power die package of claim 1, wherein the flag is rectangular, and the power lead is adjacent to the first side of the flag, and the signal lead is spaced around the remaining three other faces of the flag.

6. The power die package of claim 1, further comprising a molding compound encapsulating the flag, the proximal end of the power lead, the signal lead, the control die, the power die, and electrical connections between the power lead and the power die electrodes and between the signal lead and the first set of control die electrodes, wherein the bottom surface of the power die is exposed.

7. The power die package of claim 6, further comprising a solder layer formed on the exposed bottom surface of the power die, and wherein the package comprises a square flat no-lead (QFN) package.

8. The power die package according to claim 7, wherein: The distal ends of the signal lead and the power lead are located in a first plane, and the proximal end of the power lead and the flag base are located in a second plane, wherein the second plane is parallel to and spaced apart from the first plane, such that the proximal end of the power lead is positioned on top of and in electrical contact with the first set of power die electrodes; The active surface of the power die is attached to the lower surface of the flag base with conductive epoxy resin, and the proximal end of the power lead is also attached to the first set of power die electrodes with conductive epoxy resin. The control die has a smaller footprint than the flag base, such that the control die is arranged within the footprint of the flag base; and The control core is attached to the flag base with a core-attach adhesive tape.

9. A method for assembling a power die package, comprising: A lead frame is provided, the lead frame including a flag seat having an upper surface for receiving a control die and a lower surface for receiving a power die, a plurality of power leads adjacent to and spaced apart from a first side of the flag seat, and a plurality of signal leads adjacent to and spaced apart from at least one other side of the flag seat, wherein the plurality of power leads and the plurality of signal leads have the same thickness, and the power leads have a proximal end near the flag seat and a distal end spaced further away from the flag seat; The active surface of the power die is attached to the lower surface of the flag base, wherein the power die has a larger footprint than the flag base, such that a portion of the power die is suspended above the flag base, and wherein the portion of the power die suspended above the flag base has a plurality of power die electrodes, the plurality of power die electrodes including a first set of power die electrodes that are in contact with and in electrical communication with the proximal end of the power lead. The back side of the control die is attached to the upper surface of the flag base, wherein the active surface of the control die opposite to the back side of the control die includes a plurality of control die electrodes. The first set of control die electrodes is electrically connected to the plurality of signal leads by a first bonding line; The second set of control die electrodes is electrically connected to a second set of power die electrodes that is different from the first set of power die electrodes via a second bonding line.

10. The method of claim 9, further comprising: The flag base, the proximal end of the power lead, the signal lead, the control die, the power die, the electrical connection between the power lead and the first set of power die electrodes, and the first bonding wire are encapsulated in a molding compound, wherein the bottom surface of the power die is exposed.

11. The method of claim 9, further comprising: A solder layer is formed on the exposed bottom surface of the power die.

12. The method according to claim 9, wherein: The distal ends of the signal lead and the power lead are located in a first plane, and the proximal end of the power lead and the flag base are located in a second plane; The second plane is parallel to and spaced apart from the first plane, such that the proximal end of the power lead is positioned on top of and in electrical contact with the first set of power die electrodes; and The power die is attached to the flag base with conductive epoxy resin, and the control die is attached to the flag base with non-conductive die-attachment adhesive.

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