Method of providing a variable-pitch leadframe assembly

Abstract: A variable pitch tab leadframe assembly (103) has a plurality of patterned conductive elements (107) for transmitting input and output signals to bonding locations on an electronic device. The leadframe assembly comprises conductive elements with a variable pitch to accommodate a plurality of standard pitch bond site printed circuit board footprints.

Description: Field of the Invention The present invention relates to the field of electronic component manufacturing and packaging. Background of the Invention A problem in the prior art of electronic component packaging includes inefficient steps in the production of leadframes for bonding with variably sized and pitched component packages. The substantial inefficiencies inherent in requiring different leadframes to be manufactured for connecting different packages to printed circuit boards is both costly and wasteful. However, by providing a method of forming a universal tab leadframe which may be utilized, by only slight modification, with variably pitched packages, then cost and material savings combine to greatly improve the manufacturing and packaging processes. The present invention overcomes the problems identified above. European Patent Specification EP-A-0212890 relates to the formation of a variable pitch leadframe for connecting bonding locations of a semiconductor device to bonding sites on a circuit board in a different pitch from the bonding location. Another similar arrangement is disclosed in European Patent Specification EP-A-02499834. The present invention provides a method of providing a variable pitch tab leadframe assembly which permits electrical connection between bonding locations (110) on a semiconductor device and a plurality of bonding sites on a circuit board, the pitch of said bonding sites and said bonding locations being different, said method comprising the following steps: a) providing a variable pitch tab leadframe assembly (103) comprising a plurality of patterned conductive elements (107); b) arranging the pattern of the leadframe conductive elements to provide a first section (130), a second section (132), and at least one third section (134); each section comprising adjacent conductive elements (107) arranged in parallel and with each section comprising pitch spacing (P1, P2, P3) that is different from the other sections, said first section forming an inner end portion (107) in which the conductive elements are adapted for connection to said bonding locations (110); c) positioning a leadframe conductive element fourth section (133) in connection with the first (130) and second (132) sections, and a fifth section (135) in connection with the second section (132) and the third section (134), and sixth sections connecting further ones of said at least one third section, so that adjacent conductive elements (107) in each of the fourth (133) fifth (135) and sixth sections are positioned in non-parallel relation; and d) severing said plurality of conductive elements at one of said third sections, said remaining outer portions (123) being adapted to be bonded to said plurality of bonding sites. Figure 1 is a top fragmentary view of a variable pitch tab leadframe. Figure 2 is a top plan view of a representative tape leadframe illustrating four sections generally analogous to that shown in Figure 1 to form a complete variable pitch tab leadframe about a central package area. Figure 3 is a top plan schematic view of the second end portions of adjacent conductive elements of a variable pitch tab leadframe having a first pitch at bond pads of a next level of packaging, as known from the priort art. Figure 4 is a top plan schematic view of the second end portions of adjacent conductive elements of a variable pitch tab leadframe having a second pitch at bond pads of a next level of packaging. Figure 5 is a top plan schematic view of the second end portions of adjacent conductive elements of a variable pitch tab leadframe having a third pitch at bond pads of a next level of packaging. Detailed Description of the Preferred Embodiments Detailed preferred embodiments of the present invention are disclosed. It is to be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed are not to be interpreted as limiting, but rather as a representative basis for one skilled in the art. It will be understood that in some circumstances relevant material thicknesses and relative component sizes may be shown exaggerated to facilitate an understanding of the invention. The invention described in the present application relates to improvements in manufacturing and packaging of electronic components to achieve improved reliability, improved yield, and greater material and manufacturing efficiencies. A problem within the field of electronic component packaging involves the manner of connecting leadframe conductive elements to variously spaced next levels of packaging. It is quite common for manufacturers of conductive leadframes, such as tab leadframes, to design different leadframes to match differently pitched printed circuit board footprints. However, prior art leadframes do not have structure enabling the leadframes to be used with only slight modification with differently pitched next level of packaging bond site patterns. Therefore, what has been needed has been a method of providing an efficient and variable pitch tab leadframe assembly as partially shown in the fragmentary view of Figure 1. Referring to Figure 1, a fragmentary view of a variable pitched tab leadframe assembly 103 is illustrated in which a plurality of substantially identical leadframe assembly segments 104 are shown each comprising patterned conductive elements 107 for transmitting input and output signals to bonding locations 110 on an electronic device. Variable pitch tab leadframe assembly 103 also comprises means for providing a variable pitch to conductive elements 107 to accommodate a plurality of standard pitch bond site printed circuit board footprints, such as footprints designated by JEDEC standards. Figure 1 shows a fragment of a typical tab leadframe assembly as provided by the method of the present invention and may be appreciated more fully in the context of Figure 2 which illustrates, in dotted lines, the relative relation of the fragment of Figure 1 when combined with other fragments to form a complete representative outline of a typical variable pitch tab leadframe assembly 103 positioned preferably as one of a plurality of such leadframe assemblies on a sprocketed tape 112. In Figures 1 and 2, a central region labelled 116 represents the area in which a die, a semiconductor chip, or the like, is placed for interconnection with variable pitch tab leadframe assembly 103. Variable pitch tab leadframe assembly segment 104 comprises means for providing a variable pitch to conductive elements 107, conductive elements 107 each comprising a first end portion 120 arranged for connection with a semiconductor chip package located in area 116. Each conductive element also comprises a second end portion 123, the location of which is selected by the manufacturer, which is arranged for connection with a next level of packaging. Preferably, first end portions 120 of adjacent conductive elements have a first pitch spacing, and second end portions 123 of said adjacent conductive elements have a second pitch spacing which is different than the first pitch spacing. In Figure 1, this relationship is represented by adjacent conductive elements first and second end portions labelled 120a, 120b, and 123a, 123b respectively. Variable pitch tab leadframe assembly segments 104 may comprise a plurality of parallel sections each having a pitch spacing corresponding to, for example, a JEDEC standard pitch spacing commonly used within the field of component packaging. For example, the pitch spacing between lead second end portions may be 50 mils (1.25mm), 40 mils (1.0mm), 25 mils (.625mm), 20 mils (0.5mm), or even less. However, as the number of leads increases and greater density of packaging is pursued, the pitch of packaging continues to decrease. Yet each time a different pitch is used on a package, it may require a package leadframe-to-board spacing specifically for that pitch. Thus, the method according to the invention provides leadframe assembly segments 104 which comprise conductive elements 107 for connection with a package such that the package may be connected to variously pitched next levels of packaging, and vice versa. This may be accomplished by taking a tightly pitched package and attaching a leadframe to it that has and relies on the tab design to change the leadframe-to-board pitch. Tab leadframe assembly segment 104 preferably comprises interconnect sites which are fanned out along each conductive element to various desired pitches. This permits the chip manufacturer to provide a packaged device to a variety of users depending upon the user's sophistication in bonding devices to next levels of packaging using tight pitches. In other words, one size of variable pitch tab leadframe assemblies 103 may be used on many differently pitched printed circuit boards and package arrangements by cutting conductive elements 107 for desired pitch lengths at second ends 123 from a plurality of preexisting second end pitch patterns on conductive elements 107. This results in substantial savings in that manufacturers do not have to tool new leadframes and packages for each different board or user requirement. It is to be understood that pitch spacing greater than or less than those exemplary pitch spacings indicated above are envisioned within the scope of this invention, as is the number of parallel sections on conductive elements 107 for achieving numerous different pitches. Figure 1, therefore, illustrates a variable pitch tab leadframe assembly 103 provided by the method of the present invention for providing connection between a semiconductor chip package, which would be located in area 116, and a next level of packaging, which would be located in an area generally designated 126 corresponding to a printed circuit board or the like. Variable pitch tab leadframe assembly 103 also preferably comprises leadframe assembly segments 104 comprising a plurality of patterned conductive elements 107 for transmitting input and output signals to bonding locations on an electronic device. Variable pitch tab leadframe assembly 103 also preferably comprises means for providing a variable pitch pattern to conductive elements 107 each comprising a first section 130 and a second section 132 in which adjacent conductive elements are arranged in parallel, and a third section 133 in which adjacent conductive elements 107 are in non-parallel, the first and second sections being connected by the third section. Also, each conductive element 107 preferably comprises a first end portion 120 for connection with a semiconductor chip package and a second end portion 123 for connection with a next level of packaging. It is to be understood that second end portions 123 may be located at various lengths or pitches, as shown in Figures 1-5, whereby Fig. 3 corresponds to the arrangement known from the priort art. First end portions 120 of adjacent conductive elements 107 preferably have a first pitch spacing and second end portions 123 of said adjacent conductive elements 107 have a second pitch spacing which is different than the first pitch spacing. Thus, the pitch spacing on preferred variable pitch tab leadframe assembly 103 between adjacent conductive elements 107 differs between the first and second sections. Although various pitch spacings may be utilized in a variable pitch tab leadframe assembly 103 of the present invention, first end portions 120 of adjacent conductive elements 107 are spaced at any practicable pitch. Similarly, the corresponding second end portions of adjacent conductive elements 107 may be spaced at a pitch of generally between about 5 mils(0.125mm) and 50 mils (1.25mm). It is appreciated that the next level of packaging user will determine the appropriate pitch for leadframe-to-board attach. For example, as illustrated in Figures 3-5, adjacent conductive element second end portions 123 comprise different pitches depending on where the conductive elements 107 are severed, as determined by the pitch of the bond sites at the next level of packaging. In Figure 3, second end portions 123 are shown positioned at corresponding bond pads 130 having a pitch P1. In contrast, Figure 4 illustrates a next level of packaging requirement with bond pads 140 having a pitch P2 that is different from pitch P1. Similarly, Figure 5 illustrates another packaging requirement for which a pitch P3 exists between bond pads 150. No prior art tab leadframe assembly method is known or available to accommodate the multiple next level of packaging pitch requirements as depicted in Figures 3-5 or more. However, variable pitch tab leadframe assembly 103 may be used for various pitch requirements with the great advantages of simplicity, material efficiency, and savings of electronic packaging time, and is thus preferred. The method of providing a tab leadframe assembly permits electrical connection between a semiconductor chip package and a next level of packaging comprising various steps. These steps preferably comprise providing a leadframe as shown substantially as in Figure 1 comprising a plurality of patterned conductive elements; arranging the pattern of the leadframe conductive elements to provide a first section 130, a second section 132, and a third section 134 in which adjacent conductive elements are arranged in parallel, and a fourth section 133 and a fifth section 135 in which adjacent conductive elements are arranged in non-parallel fanned relation and which provide interconnection between the first, second, and third sections. Further, the step of arranging the pattern of the leadframe conductive elements may comprise providing a plurality of first, second, and third sections so that the pitch spacing of adjacent conductive elements differs between the first, second, and third sections. Further sections may be included following the above method of manufacture.

Claims: A method of providing a variable pitch tab leadframe assembly which permits electrical connection between bonding locations (110) on a semiconductor device and a plurality of bonding sites on a circuit board, the pitch of said bonding sites and said bonding locations being different, said method comprising the following steps: a) providing a variable pitch tab leadframe assembly (103) comprising a plurality of patterned conductive elements (107); b) arranging the pattern of the leadframe conductive elements to provide a first section (130), a second section (132), and at least one third section (134); each section comprising adjacent conductive elements (107) arranged in parallel and with each section comprising pitch spacing (P1, P2, P3) that is different from the other sections, said first section forming an inner end portion (107) in which the conductive elements are adapted for connection to said bonding locations (110); c) positioning a leadframe conductive element fourth section (133) in connection with the first (130) and second (132) sections, and a fifth section (135) in connection with the second section (132) and the third section (134), and sixth sections connecting further ones of said at least one third section, so that adjacent conductive elements (107) in each of the fourth (133) fifth (135) and sixth sections are positioned in a non-parallel fanned relation; and d) severing said plurality of conductive elements at one of said third sections, said remaining outer portions (123) being adapted to be bonded to said plurality of bonding sites.

Inventors: DUNAWAY THOMAS J, POPLETT JAMES M, SPIELBERGER RICHARD K, DUNAWAY, THOMAS J., POPLETT, JAMES M., SPIELBERGER, RICHARD K.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1990
Main classification: H01L21
IPC codes: H05K3, H01L21, H01L23