The present invention generally relates to non-leaded semiconductor devices, and, more particularly, to a method of singulating non-leaded devices.
Leaded semiconductor devices have leads that extend from a main package body. Non-leaded devices, such as Quad Flat No-leads (QFN) devices, are similar to leaded semiconductor devices except that the leads do not extend outwardly or project from the package body. Rather, the leads are generally flush with the package body. Non-leaded devices have become very popular because they have a smaller footprint than traditional leaded devices. Non-leaded devices also require fewer backend process steps since the leads do not need to be formed or bent, such as into a gull wing shape. However, because the leads lie in the same plane as the package body, burrs on the lead ends, formed during singulation (when the package is separated from an adjacent, simultaneously formed package), can cause issues for proper Printed Circuit Board (PCB) mounting. Another issue caused during singulation is smearing of the metal of the leads. Smearing is caused by the heat and friction from the saw blade, and is a problem because, in some cases, smearing can cause shorting between adjacent leads.
Accordingly, it would be advantageous to be able to singulate adjacent, simultaneously assembled devices without forming burrs on the leads or lead tips, or smearing the metal of the leads.
So that the manner in which the features of the present invention can be understood in detail, a detailed description of the invention is provided below with reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. The drawings are for facilitating an understanding of the invention and thus are not necessarily drawn to scale, and some features may be omitted in order to highlight other features of the invention so that the invention may be more clearly understood. Advantages of the subject matter claimed will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings, in which like reference numerals have been used to designate like elements, and in which:
In one embodiment, the present invention provides a no-leads semiconductor device, such as a Quad Flat No-leads (QFN) device. The device includes an integrated circuit (IC) die, and a plurality of lead fingers spaced from and projecting outwardly from at least one side of the IC die. Electrodes of the IC die are electrically connected to proximal portions of respective ones of the lead fingers. A housing encases the IC die, the lead fingers, and the connections therebetween. The housing has opposing top and bottom surfaces, and side surfaces that extend between the top and bottom surfaces. Distal ends of the leads are exposed at the bottom and the at least one side surface of the housing, and the exposed distal ends are flush with the bottom surface. There also is a first notch in the exposed portions of each of the leads. The first notch offsets a portion of the distal end of the lead from the side surface. The notch is formed as a consequence of scribing saw streets of simultaneously assembled devices prior to singulating the devices.
In another embodiment, the present invention provides a method of singulating no-lead semiconductor devices assembled on a lead frame array. The method includes performing a first scribing operation on a first side of a saw street of the lead frame array, thereby forming a first scribe line, and performing a second scribing operation on a second side of the saw street, thereby forming a second scribe line. Cutting between the first and second scribe lines is then performed with a saw, thereby separating adjacent, simultaneously formed no-lead semiconductor devices. The first and second scribing operations form a notch in exposed portions of the leads at edges of the devices.
Referring now to
As is known in the art, to assemble a semiconductor device, an integrated circuit die is attached to a die receiving area of a lead frame and then the die is electrically connected to leads or lead fingers of the lead frame, such as with bond wires or flip-chip interconnects. Then the assembly is covered with a molding compound. Using the lead frame strip 100, a plurality of semiconductor devices may be simultaneously assembled. After molding, singulation is performed to separate the devices from each other. Singulation is performed by cutting with a saw blade along saw streets, which in
The lead frames 102 each comprise a central die receiving area 104, e.g., a die pad that is sized and shaped to receive a semiconductor die and thus, the size of the die pad generally is based on the size of the die. In the embodiment shown, the die pad 104 is rectangular, but this is not a requirement. The lead frames 102 also have a plurality of leads 106 that extend away from at least one lateral side of the central area or die pad 104. In the embodiment shown, the leads 106 surround the die pad 104 and extend away from all four lateral sides of the die pad 104. However, as will be understood by those of skill in the art, the leads 106 may extend from just two opposing lateral sides of the die pad 104. The leads 106 each have a proximal end near to but spaced from the die pad 104 and a distal end 112 that is connected to a lead of an adjacent lead frame (at a saw street) if there is one, or to a part of the frame of the lead frame strip 100 (which also would be at a saw street).
Integrated circuit dies 108 are attached to the die pads 104 during the assembly process. The dies 104 are attached to the die pads 104 of the lead frames 102 using a die attach material, such as an adhesive or adhesive tape, as is known in the art. In one embodiment, the adhesive is thermally conductive, so that heat generated by the semiconductor die 108 can be dissipated through the die pad 104. In another embodiment, the adhesive is both electrically and thermally conductive for providing additional connection between the semiconductor die 108 and the die pad 104. In one embodiment, the adhesive comprises an epoxy paste that is printed onto the die pad 104. After the semiconductor die 108 is attached to the die pad 104, the adhesive is cured so that the semiconductor die 108 is securely fastened to the die pad 104.
The semiconductor die 108 may be any type of die, such as a sensor die, a power die, an application specific integrated circuit (ASIC), etc. The semiconductor die 108 may have an active region on one side thereof and a non-active region on an opposite side. In the presently preferred embodiment, the semiconductor die 108 is placed on the die pad 104 such that the non-active region side faces the die pad 104. In another embodiment, the active region side of the semiconductor die 108 can be configured to face the die pad 104 and connect to the leads 106 with bumps or flip-chip connections.
When the semiconductor die 108 is mounted on the die pad 104 with its non-active region side attached to the die pad 104, then bond wires 110 are used to electrically connect the semiconductor die 108 to the proximal ends of the leads 106. That is, the electrodes on the active side surface of the semiconductor die 108 are electrically connected to the proximal ends of the leads 106 with the bond wires 110. The bond wires 110 can be any kind of bond wires, such as copper or gold, and may be coated or uncoated.
After attaching and electrically connecting the semiconductor dies 108 to the lead frames 102, the dies 108, bond wires 110 and at least the proximal ends of the leads 106 are covered with a molding compound (not shown in
After molding, the lead frame strip 100 is singulated, whereby the assemblies are separated and the frame is cut away by cutting along the saw streets A-A and B-B. Additional saw streets cutting the frame away are not shown just for the sake of clarity.
Referring now to
The scribing and cutting operations form a first notch 142 in the lateral side wall of the finished devices 120 and 122. The distal ends of the leads 124 and 126 are exposed at and flush with the bottom surface of the finished devices 120 and 122. Further, the lateral side walls of the finished devices 120 and 122, include exposed portions of the leads 124 and 126, and the first notch 142. The first notchs 142 offset a portion of the distal ends of the leads 124 and 126 from the side surface of the devices 120 and 122. It also should be noted that an exposed surface of each of the leads 124 and 126 at the side surface of the housing is not plated with a metal or metal alloy, as the inner portions of the leads, now exposed, were not plated. Of course, as will be understood by those of skill in the art, the exposed portions of the underlying Copper could be plated after singulation.
The scribing and cutting operations form a first notch 166 in the lateral side wall of the finished devices. Further, since in this embodiment, the saw street part of the leads 154 and 156 already included a channel so the saw blade would not have to cut through so much metal, the finished devices 150 and 152 have a second notch 168. Thus, where the leads 154 and 156 generally are flush with the bottom surface of the devices 150, 152, respectively, the exposed portions of the leads 154 and 156 on the device sidewalls include the first and second notches 166 and 168.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the subject matter (particularly in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.
Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the scope of protection sought is defined by the claims as set forth hereinafter together with any equivalents thereof entitled to. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illustrate the subject matter and does not pose a limitation on the scope of the subject matter unless otherwise claimed. The use of the term “based on” and other like phrases indicating a condition for bringing about a result, both in the claims and in the written description, is not intended to foreclose any other conditions that bring about that result. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as claimed.
Preferred embodiments are described herein, including the best mode known to the inventor for carrying out the claimed subject matter. Of course, variations of those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the claimed subject matter to be practiced otherwise than as specifically described herein. Accordingly, this claimed subject matter includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed unless otherwise indicated herein or otherwise clearly contradicted by context.