Patent Application
20210005569
This disclosure relates to integrated circuit (IC) packages, and more particularly, to an IC packages that implement a gang clip.
Increasing power levels and power density requirements for multiple end products means that high-power semiconductor modules and components are often assembled using a clip-bonding technology. Solder paste leaves flux residues on solder joints and must be cleaned from high-power modules to meet high reliability requirements.
In contrast to the techniques of attaching a die by adhesive bonding or wire soldering, high-power packages and discrete devices, such as metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and switched output differential structures (SODs) use solder paste to connect the die to the basic substrate and/or leads. Clip-bonding technology partially replaces the standard wire-bond connection between a die and a lead by a clip (e.g., a copper clip), which is also soldered by solder paste. Clip bonding allows for unique package resistance, better thermal transfer, and ultra-fast switching performance due to the small package.
One example relates to an integrated circuit (IC) package having a lead frame and a first die adhered to the lead frame on a first side of the first die. The IC package also includes a first clip having a clip foot adhered to the lead frame, the first clip extending from the lead frame and contacting a second side of the first die on a first side of the first clip via a first layer of solder paste wherein the second side of the first die opposes the first side of the first die. The IC package further includes a second die with a first side adhered to a second side of the first clip via a second layer of solder paste, wherein the second side of the first clip opposes the first side of the first clip. The IC package still further includes a second clip having a clip foot adhered to the lead frame on a first side of the second clip, the second clip extending from the lead frame to a second side of the second die via a third layer of solder paste. The second side of the second die opposes the first side of the second die, wherein the second clip has an sawn or lased edge on a second side of the second clip, wherein the second side of the second clip opposes the first side of the second clip.
Another example relates to a method for forming an IC package. The method includes forming a first layer of solder paste on a lead frame. The method also includes adhering a first die to the lead frame on a first side of the first die via the first layer of solder paste. The method further includes forming a second layer of solder paste on a second side of the first die, the second side of the first die opposing the first side of the first die. The method yet further includes adhering a clip foot of a clip to the lead frame and adhering a first side of the first clip to the second side of the first die via the second layer of solder paste. The method still further includes forming a third layer of solder paste on a second side of the first clip. The second side of the first clip opposes the first side of the first clip and adhering a second die on the second side of the first clip via the third layer of solder paste. The method also includes forming a fourth layer of solder paste on a first side of a second clip and adhering a first clip foot on a first side of the second clip to the lead frame and adhering the second clip to the second side of the second die via the fourth layer of solder paste, and wherein a second clip foot on a second side of the second clip rests on the lead frame on that opposes the first side of the second clip. The method further includes reflowing the first layer, the second layer, the third layer and the fourth layer of solder paste.
Yet another relates to an IC package including a lead frame a first die attached to the lead frame and a first clip attached to first die and the lead frame. The IC package also includes a second die attached to first clip and the lead frame and a second clip with a clip foot adhered to the lead frame on a first side of the second clip. The second clip extending to and contacting a side of the second die via a layer of solder paste. The second clip includes a sawn or lased edge at a second side of the second clip that opposes the first side of the second clip.
This disclosure relates to an IC package with a clip, such as a gang clip. The gang clip refers to a clip that overlays a plurality of frames in a lead frame. The clipped die structure includes a first clip (e.g., a copper clip) sandwiched between a first die and a second die. A second clip (e.g., a gang clip) includes a first clip foot adhered to a lead frame. The second clip also includes a high side that overhangs the clipped die structure and contacts a side of the second die via a layer of solder paste. The second clip initially includes a second foot (e.g., a dummy foot) that rests against the lead frame to prevent tilting of the second clip and the clip of the clipped die structure during solder reflow. Furthermore, during singulation, the second clip foot is removed in a sawing or lasing process. The prevention of tilting ensures that the layer of solder paste between the second clip and the second die has a nearly constant thickness bond line thickness (BLT) (e.g., within 10 micrometers (μm). Additionally, the prevention of tilting prevents an unwanted short between the second clip and the second die.
A bottom of a first die 104 overlaying the lead frame 102 is adhered and coupled to a first portion 103 of the lead frame 102 via a first layer of solder paste 106. A second layer of solder paste 108 overlays the first die 104. For purposes of simplification of explanation the terms top and bottom are employed throughout this disclosure to denote opposing surfaces. Similarly, the terms overlay, underlie, vertical and horizontal (and their derivatives) are employed to denote relative positions in a described arrangement. Moreover, the examples used throughout this disclosure denote one possible orientation. However, other orientations are possible (e.g., upside down, rotated by 90 degrees, etc.).
A first clip 110 includes a clip foot 112 adhered to a second portion 113 of the lead frame 102 via solder paste 114. As used herein, the term “clip” refers to a rigid copper bridge employed to implement clip bonding between a lead frame (e.g., the second portion 113 of the lead frame 102) and one or more dies (e.g., the first die 104) of an IC package (e.g., the IC package 100). Additionally, as used herein, the term “clip foot” refers to a region a clip that is adhered to a lead frame. In some examples, the solder paste 114 is formed with the first layer of solder paste 108 in a prior etching process. The first clip 110 extends from the clip foot 112 to a high side 116 via a tilted pillar 117 of the first clip 110. The high side 116 is implemented as a cantilever (e.g., a beam) that overlays the first die 104. The high side 116 of the first clip 110 is adhered and electrically coupled to the first die 104 via the second layer of solder paste 108. The high side 116 applies a force in a direction indicated by an arrow 120 (e.g., a downward force).
A third layer of solder paste 122 overlays the first clip 110. Additionally, a second die 124 overlays the first clip 110. More particularly, the second die 124 is adhered and, in some examples, electrically coupled to the first clip 110 via the third layer of solder paste 122. Moreover, in some examples, the second die 124 has a smaller footprint than the first die 104. In the example illustrated, the IC package 100 includes a clipped die structure 123 that is representative of the first clip 110 sandwiched between the first die 104 and the second die 124 via the second layer of solder paste 108 and the third layer of solder paste 122. The clipped die structure 123 also refers to the first portion 103 of the lead frame 102 and the second portion 113 of the lead frame 102, as well as portion of the first layer of solder paste 106 that couples the first die 104 to the lead frame 102 and the portion of solder paste 114 that couples the first clip 110 to the second portion 113 of the lead frame.
A second clip 130, such as a gang clip, includes a first clip foot 132 adhered to a third portion 133 of the lead frame 102 on via a solder paste 134. In some examples, the second clip 130 is a solid copper bridge (e.g., a copper clip). Additionally, in some examples, the second clip 130 represents a singulated portion of a larger second clip that (prior to singulation) contacted multiple dies in an array of IC structures. A corner of the first clip foot 132 is adhered to the third portion 133 of the lead frame 102. The solder paste 134 is a partition of the first layer of solder paste 106 that has been etched away. The second clip 130 includes a tilted pillar 136 extending from the first clip foot 132 of the second clip 130 to a high side 138 of the second clip 130. The high side 138 of the second clip 130 is a planer region on the second clip 130. In some examples, the tilted pillar 136 of the second clip 130 extends from the first clip foot 132 at an oblique angle. Stated differently, the tilted pillar 136 of the second clip 130 extends from the lead frame 102 at an angle other than 90 degrees.
In the example illustrated, the uneven BLT of the solder paste, after reflow results in the second clip 202 directly contacting the second die 208. More specifically, the second clip 202 directly contacts the second die 208 without intermediate solder paste, resulting in a short circuit indicated at 213 between the second clip 202 and the second die 208. In some examples if the pivot of the second clip 202 is too extreme during reflow of the solder paste 210, the second clip 202 may contact the first clip 204 in another short indicated near an area indicated at 214.
Referring back to
The high side 138 of the second clip 130 is implemented as a cantilever (e.g., a beam) that is adhered, and in some examples electrically coupled to the second die 124 via a fourth layer of solder paste 141. In some examples, the fourth layer of solder paste 141 is implemented as a solder pillar. During reflow of solder, the high side 138 is shaped to apply a force indicated by an arrow 152 (e.g., an upward force). In some examples, the reflow process of the solder paste includes a reflowing of the first layer of solder paste 106, the second layer of solder paste 108, the third layer of solder paste 122 and the fourth layer of solder paste 141. During the reflow process, the second clip foot 140 of the second clip 130 prevents tilting (or pivoting) of the second clip 130. The prevention of the tilting (e.g., anti-tilting) results in a nearly constant (e.g., within 10 μm) BLT throughout the area of the fourth layer of solder paste 141. Further, in some examples, during the reflow process, the force 152 opposes the force 120, such that the first clip 110 is also prevented from tilting or pivoting. In this situation, the first layer of solder paste 106, the second layer of solder paste 108 and the third layer of solder paste 122 (or some subset thereof) also have a nearly constant BLT (e.g., within 10 μm).
After reflow, the IC package 100 is cut (e.g., sawn or lased) through the saw street 150, thereby removing the fourth portion 142 of the lead frame 102, the second tilted pillar 144 and a portion of the high side 138 of the second clip 130. However, after reflow, the solder paste, including the first layer of solder paste 106, the second layer of solder paste 108, the third layer of solder paste 122 and the fourth layer of solder paste 141 are rigid (e.g., hardened), and further extrusion of the solder paste is avoided. Additionally, the second clip 130 avoids direct contact with the second die 124. Stated differently, the second clip 130 contacts, and in some examples, is electrically coupled to the second die 124 only through the fourth layer of solder paste 141. Furthermore, the resultant second clip 130 includes an edge 154 that has been sawn or lased (alternatively referred to as a sawn or lased edge) that has residue remnant from the sawn off portion of the high side 138 of the second clip 130. The edge 154 of the second clip 130 is on a side of the second clip 130 that opposes the side of the second clip 130 with the first clip foot 132. In the resultant IC package 100, the high side 138 of the second clip 130 overhangs the first clip 110. More particularly, the high side 138 extends over the first clip 110, including the tilted pillar 117 of the first clip 110. Moreover, the edge 154 abuts the saw street 150, such that the edge 154 of the second clip 130 is parallel to an edge 155 of the lead frame 102 because the second clip foot 140 prevented tilting of the second clip 130 during removal (sawing of lasing) of the second tilted pillar 144 and the portion of the high side 138 of the second clip 130. Additionally, in some examples, the high side 138 of the second clip 130 has residue 156 remnant from a tie bar or multiple tie bars on a surface of the high side of that is orthogonal to the edge 154.
The first portion 303 and the second portion 305 of clip 300 are configured to be adhered to a die. More particularly, the first portion 303 and the second portion 305 of the clip 300 are configured to be positioned to overlay a die of a respective IC structure and each high side 307 is adhered to the respective die via the solder pillar 308. In such a situation, upon reflow of the solder pillar 308, the clip tilts (e.g., pivots about corner the clip foot 302), such that the solder pillar 308 between the respective die and the high side 307 has an uneven BLT and/or a short between the clip 300 and the die.
As noted, the clip 300 includes the first portion 303 for a first IC package structure and the second portion 305 for a second IC package structure. In such a situation, the clip 300 can be a constituent component for more IC packages, as discussed herein. In such a situation, a beam 330 extends horizontally across the clip 300. Moreover, during singulation, a saw street 332 of the first portion 303 and the second portion 305 of the clip 300 are sawn through during singulation.
The second tilted pillar 412 of the first portion 403 and the second portion 405 also extends from the substrate 408 at an oblique angle. In some examples, the second tilted pillar 412 extends from the substrate 408 at a different angle than the first tilted pillar 406. In other examples, the second tilted pillar 412 extends from the substrate 408 at the same angle as the first tilted pillar 406.
The first portion 403 and the second portion 405 of the clip 400 are configured to be adhered to a respective die, such as the second die 124 of
The second clip foot 404, the second tilted pillar 412 and a portion of the high side 410 are removable from the first portion 403 and the second portion 405 of the clip 400 after the reflow of the solder. In particular, after reflow and during singulation, a saw street 420 of the first portion 403 and the second portion 405 is sawn with a saw or a laser to remove material and to define an edge 422 in the high side 410. In some examples, the edge 422 includes an interface with remnant residue from the sawn off portion of the high side 410.
As noted, the clip 400 includes the first portion 403 for a first IC package and the second portion 405 for a second IC package. In such a situation, the clip 400 can be a constituent component for more IC packages, as discussed herein. In such a situation, a beam 430 extends horizontally across the clip 400. Furthermore, in some examples, the clip 400 can be merged with the clip 300 of
The free body diagram 500 includes lines representing different forces applied on the clip 502. The free body diagram 500 includes a first force, F1 that presents a downward force applied by the die 504. The first force, F1 is separated by a pivot point, P1 by a first distance, D1. The free body diagram 500 also includes a weight, W representing a force due to gravity. The free body diagram 500 includes a second force, F2 representing a net downward force. The free body diagram 500 includes a reactive force, R1 SIN θ, which is representative of an angled upward force applied by the clip foot 508 and the tilted pillar 510. The free body diagram 500 includes a first reactive force, R1 representative of a net upward force at a distance D2 from the weight, W.
Inclusion of the second clip such as the second clip 130 of
The first IC structure 602 and the second IC structure 604 each include a die 606. During a packaging process, a second clip 608, such as the second clip 300 of
The IC structure 620 in the final row (e.g., the 15 row) of the sixth column is also illustrated in an expanded view. However, the final row (e.g., the fifteenth row), there is no subsequent IC structure on which any portion of the second clip 608 rests. Thus, the second clip 608 includes a fifteenth clip foot 623 and a dummy clip foot 624 (e.g., the at least one extra clip foot) that is positioned in a saw street 626 of the IC structure 620. In this manner, during packaging, the second clip 608 of associated with the IC structure 620 has two clip feet, namely, a first clip foot 623 (the fifteenth clip foot overall) and a second clip foot 624 (the dummy clip foot). The second clip 608 can be implemented, for example, as the first portion 403 or the second portion 405 of the clip 400 illustrated in
In some examples, the second clip 608 employed for each row (or some subset thereof) of in the panel 600 includes a dummy foot (similar to the dummy clip foot 624) that is removed during singulation. In other examples, the second clip 608 includes a dummy foot (e.g., the dummy clip foot 624) in a last row.
Inclusion of the second clip foot 712 prevents tilting of the second clip 702 during solder reflow, as discussed herein. Further, the second clip 702 provides an upward force on a clip (hidden from view in
At 825, a second die (e.g., the second die 124 of
What have been described above are examples. It is, of course, not possible to describe every conceivable combination of components or methodologies, but one of ordinary skill in the art will recognize that many further combinations and permutations are possible. Accordingly, the disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements.
