Patent Application
20150311143
The present invention relates generally to semiconductor packaging, and, more particularly, to lead frames used in assembling semiconductor devices.
Referring to
In this particular embodiment, the lead frame 102 includes (i) a die flag 106 (also known as a die pad or die paddle), (ii) a plurality of leads 112, (iii) four corner pads 108, and (iv) four linear edge traces 110. The linear edge traces 110 connect different pairs of adjacent ones of the corner pads 108.
Each lead 112 has (i) an external pad area 114 that allows the assembled device to be connected to other devices or a printed circuit board, (ii) a wire-bond pad 118 where a bond wire is attached for connecting the lead 112 to an IC die (not shown) subsequently mounted on the die flag 106, and (iii) a lead trace 116 connecting the external pad area 114 to the wire-bond pad 118.
The external pad areas 114 are exposed or formed entirely through the encapsulant 104 so that, for example, a solder ball may be disposed on the bottom of the bond area 114 exposed on the bottom surface of the lead frame 102. The wire-bond pads 118, the lead traces 116, and the linear edge traces 110 are formed part of the way through the encapsulant 104 such that the encapsulant 104 directly under the wire-bond pads 118, the lead traces 116, and the linear edge traces 110 is thinner than in areas of the lead frame 102 where no metal structures are present.
During device assembly, one or more IC dies (not shown) are adhesively mounted on the die flag 106. Wire bonding is performed, where metal bond wires (not shown) are strung between and bonded to bond pads on each IC die and corresponding wire-bond pads 118 of the lead frame 102.
Following wire bonding, the upper surface of the lead frame 102, the IC die(s), and the bond wires are encapsulated in molding compound. The molding compound is subsequently cured. After encapsulation, solder balls (not shown) may be deposited on the exposed external pad areas 114. The solder balls, together with the leads 112, provide electrical connections between electronic components internal to the IC die and electronic components external to the packaged device. External components might include power sources and input/output connections on a printed circuit board (PCB) on which the packaged semiconductor device is mounted.
Referring to
In
The peripheral region 120 includes a plurality of cylindrical metal structures 122 (a.k.a. current stealers) embedded in the encapsulant 104. The current stealers 122 help to uniformly distribute electrical current across the surface of the lead frame array 100 during electroplating.
To separate the semiconductor packaged devices assembled on the lead frames 102a-d from one another and from the peripheral region 120, singulation is performed whereby cuts are made along dashed lines 126. Note that dashed lines 126 do not represent physical markings, but are merely provided to show where the cuts are made. Cutting along the dashed lines 126 leaves a border 128 of encapsulant 104 around the perimeter of each packaged semiconductor device as shown in
The MIS substrate or lead frame 102 is susceptible to handling and thermally induced warpage cracks along the trace-to-mold interfaces. As these lead frames 102 are ultra thin (0.112 mm total) and the mold compound 104 is thin directly below the traces, there are weaknesses in the structure. This situation is compounded when the lead frames 102 do not have a solder mask coating, which may be left off due to the increased cost involved in including such a coating. Thus, it would be beneficial to have a stronger lead frame or MIS substrate such that it is less susceptible to cracking and warpage.
Embodiments of the present invention are illustrated by way of example and are not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the thicknesses of layers and regions may be exaggerated for clarity.
Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. Embodiments of the present invention may be embodied in many alternative forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the present invention.
When the embedded lead frame array 100 of
When a crack forms, the crack tends to propagate entirely through the thickness of the lead frame array 100 and along the length of the elongated trace. For example, a crack could propagate through the lead frame 102 of
In the following description, it will be understood that certain embodiments of the present invention are directed to lead frames comprising metal features for preventing cracks such as those discussed above and articles of manufacture comprising such lead frames. Although one particular type of lead frame is described in the embodiment below, it will be understood that embodiments of the present invention are not so limited. According to alternative embodiments of the present invention, these metal features can be implemented in other suitable types of lead frames.
In one embodiment of the present invention, an article of manufacture comprises a lead frame, wherein the lead frame comprises a trace embedded in an encapsulant, and a plurality of stubs (i) embedded in the encapsulant and (ii) connected to and extending from the trace at different locations along the length of the trace.
In addition, the lead frame 202 comprises a plurality of outer metal stubs 230 and inner metal stubs 232. Each outer metal stub 230 extends from a linear edge trace 210 of a lead frame 202 to an edge of the encapsulant border 228 of the lead frame 202. Each inner metal stub 232 extends from a linear edge trace 210 of a lead frame 202 away from the peripheral edge of the lead frame 202 and terminates before reaching any other metal structures. In this embodiment, each inner stub 232 is positioned between a different pair of adjacent external pads 214 along the perimeter of lead frame 202; however, other spacings are possible. For example, the inner stubs 232 could be spaced between every other external pad 214.
The metal stubs 230 and 232 strengthen the lead frame 202 such that the lead frame 202 is less susceptible to cracking than the lead frame 102 of
Referring now to
In this embodiment, each outer metal stub 230 of each lead frame 202a-d is interconnected with either (i) an outer metal stub 230 of an adjacent lead frame or (ii) a cylindrical metal structure 222 of an adjacent portion of the peripheral region 220. The outer stubs 230 are spaced by a distance that is equal to the distance between every other cylindrical metal structure 222; however, other spacings are possible.
Overall, interconnecting the lead frames 202a-d to one another and to the peripheral region 220 using the outer metal stubs 230 provides a lead frame array structure that is more resistant to bending. Further, each metal stub 230 and 232 provides a stop that may prevent a crack from propagating along the length of a linear edge trace 210. Metal stubs 230 and 232 can be incorporated into lead frame array designs with little, if any, cost, and do not require special routing of the leads 212 to avoid the stubs 230 and 232.
Packaged semiconductor devices may be assembled on the embedded lead frames 202a-d in a manner similar to that discussed above in relation to the embedded lead frame 102 of
Although one embodiment of the present invention was described as implementing metal stubs 230 and 232 along linear edge traces 210 on the perimeter of lead frame 202, embodiments of the present invention are not so limited. In general, metal stubs may be implemented on any suitable trace of a lead frame.
For example,
Further, some embodiments of the present invention might not have linear edge traces. In such embodiments, the metal stubs may be implemented on suitable traces within the interior of a lead frame.
In general, the particular configuration of the lead frame 202 shown in
According to alternative embodiments of the present invention, metal stubs such as stubs 230 and 232 may be implemented on types of lead frames other than that shown in
Further, according to alternative embodiments of the present invention, the particular features of the lead frame 202 may vary. For example, the size and shape of the lead frame 202, the number and arrangement of the leads 212, and the size and shape of the die flag 206 may vary.
Although
Further, although
Yet further, although
Even further, although
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. For example, more than one IC die may be mounted onto the die flag 206. As another example, an IC die may be electrically connected to the leads of a lead frame of the present invention using electrical interconnections other than bond wires, such as flip-chip bumps. As yet another example, lead frames of the present invention may be formed using photolithography or other techniques.
As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It further will be understood that the terms “comprises,” “comprising,” “has,” “having,” “includes,” and/or “including” specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components. It also should be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Reference herein to “one embodiment” or “an embodiment” 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 appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
Terms of orientation such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” “right,” and “left” well as derivatives thereof (e.g., “horizontally,” “vertically,” etc.) should be construed to refer to the orientation as shown in the drawing under discussion. These terms of orientation are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation.
Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range.
Also for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. Conversely, the terms “directly coupled,” “directly connected,” etc., imply the absence of such additional elements.
In this specification including any claims, the term “each” may be used to refer to one or more specified characteristics of a plurality of previously recited elements or steps. When used with the open-ended term “comprising,” the recitation of the term “each” does not exclude additional, unrecited elements or steps. Thus, it will be understood that an apparatus may have additional, unrecited elements and a method may have additional, unrecited steps, where the additional, unrecited elements or steps do not have the one or more specified characteristics.
The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.
