Hybrid microchip bonding article

Abstract: An article for tape-automated bonding of integrated circuit microchips comprises a carrier sheet (22) (Fig. 2) carrying conductive tracks (23) with a tubular metal formation (21) passing through the sheet at the end of each track for connection to a microchip (24). The tubular formations tend to accommodate irregularities in the chip and may contain solder or other metal having a lower melting point than the tubular formation to effect bonding.

Description: This invention relates to a hybrid bonding article which is provided in arrangements suitable for use in tape-automated bonding (TAB) of semiconductor microcircuits (microchips). Known TAB devices have a structure akin to that shown schematically in the accompanying sketch A. A polymer tape A1 having edge sprocket holes A2 for feeding the tape in automated bonding equipment carries a series of arrays (one shown) of conductive tracks A3 arranged in a pattern suitable for bonding their inner ends A4 to the bonding sites of a microchip (not shown). The tape A1 is cut away under the ends A4 of the tracks so that the ends project as unsupported "fingers" over the cut-away space A5. Bonding is effected by bending the fingers into the space A5 to make contact with the chip positioned against the opposite side of the tape from that carrying the tracks. This is followed by bonding by known techniques which often require the chip bonding sites to "bumped" with bonding material, e.g. solder. The present invention can avoid such disadvantageous "bumping" processes. Another form of TAB device known as "area TAB" is described in U.S. Patents 3832769, 3868724 and 4472876, in which the conductive tracks do not project as "fingers", but instead are connected to solid metal terminals formed in holes passing through the tape material. The terminals project from the surface of the tape remote from the tracks and can therefore make electrical contact with bonding sites on micro chips or other devices brought into contact therewith. The reliability of the electrical contacts thus established may be limited by the relative rigidity of the terminals hindering their ability to conform to variations in height of the bonding sites on the chip, especially as increasing miniaturization and complexity of microchips requires bonding sites in central areas of the chip as well as around its edges. A tape-automated bonding article of this type which corresponds to the preamble of claim 1 is known from EP-A-0 171 232. The present invention alleviates these problems by means of an ingenious hybrid form of TAB article, and accordingly provides a tape-automated bonding article as specified in claim 1. The diameter of the connecting hole is preferably less than 100 micrometres, more preferably less than 50 micrometres. The holes will usually pass more or less straight through the sheet to its opposite surface (i.e., the "surface not carrying the track end"), but may be sloping or indirect (e.g. curved) if desired. Preferably, the conductive material in the connecting hole or holes which projects beyond the said surfaces so as to facilitate bonding to the microcircuit, is tubular. The projections may be achieved by removing one or more layers from the carrier sheet after plating (or other provision) of the conductive material in the connecting hole. The use of a tubular formation of conductive material (preferably metal) in the connecting holes has considered advantages over the known solid metal terminals. The tubes may crumple when compressed longitudinally against a microchip or other device, thus taking up irregularities without the major deviation from the longitudinal axis which normally results when solid columns or wires are so compressed. Also, solder or other fusible material may be provided at or within the ends (at least) of the tubes to facilitate thermal bonding and electrical connection. This hybrid TAB article according to the invention is constructed with cut-away "fingers" of the carrier sheet material supporting the conductive track ends to be bonded, thus providing a "fingered" construction corresponding to, but with advantages over, the ordinary TAB article; and may be constructed with "fingers" extending also to the central regions of the chip. For these "fingered" hybrids alternative forms of connection (e.g. solid wires or posts) may also be useful. The "fingered" construction provides advantageous flexibility in articles with central, as well as peripheral, connection sites. An example of a fingered construction according to the present invention is illustrated schematically in Figure 1 of the accompanying drawings, wherein the reference numerals correspond to the numerals used in Sketch A. The connecting holes with the tubular electrically conductive material, preferably metal, therein, one or more per track end, cannot be made by the methods described in the known "area TAB" patents mentioned above. The present invention preferably hybridizes the TAB concept with methods and materials for making self-supporting uniaxial connectors described in any one or more of copending British Patent Applications 8802567, 8802565, 8802566, 8802568, 8815447.1, and European Published Patent Applications EP-A-0213774, 0327399, 0329314 and 0327398. Laser ablation drilling of a layered polymer sheet and metal plating within the hole(s) followed by removal of one or more soluble layers from the sheet (to expose the ends of the metal tubes thus formed within the holes) is preferred. The resulting hybrid TAB article incorporating in situ tubular uniaxial connectors, with the metal TAB tracks preferably subsequently applied to its surface, represents a significant commercial advance, as aforesaid, over previously proposed TAB articles. When the sheet which ultimately contains the conductive through-holes (as distinct from any removable surface layers on such a sheet) is to comprise a polyimide material, a preferred polymer material is a substantially fully cyclised polyimide capable of retaining at least 50%, preferably at least 75%, more preferably at least 85%, of its original elongation after immersion in water of pH10 at 100°C for 4 days according to ASTM D882. It will be readily understood that a "substantially fully cyclised" polyimide is one having substantially no open imide rings or uncyclised amic acid groupings. Such a polyimide is better able to survive hot alkaline metal plating baths, which attack incompletely cyclised polyimides such as Kapton (TM). The currently preferred commercially available polyimides are those available under the Trade Mark "UPILEX" from Ube/ICI. One of these, "UPILEX R", is believed to be a relatively completely cyclised polymer having a repeat unit derived from biphenyl dianhydride and diaminodiphenylether, viz. Preferred, however, is "UPILEX S", which is believed to have a repeat unit derived from the same anhydride and phenylene diamine, viz.

Claims: A tape-automated bonding article comprising a carrier sheet of polymer material carrying on one surface at least one array of electrically conductive tracks having ends arranged for bonding to a microcircuit device, each bondable track being electrically connected to the surface of the carrier sheet which is opposite said surface carrying that track end by a formation of electrically conductive material within at least one connecting hole of diameter less than 200 micrometres, the conductive material in the connecting hole or holes projecting beyond the said surfaces so as to facilitate bonding to the microcircuit, characterised in that the carrier sheet includes fingers of the polymer material and each bondable track end is carried by a respective finger of the carrier sheet. An article according to claim 1, characterised in that the carrier sheet comprises a substantially fully cyclised polyimide and when tested according to ASTM D882 is capable of retaining at least 50% of its original elongation after immersion in water of pH10 at 100°C for 4 days. An article according to any preceding claim, characterised in that the said formation of electrically conductive material is tubular. An article according to claim 1, characterised in that at least some of the tubular formations have at or within their respective ends, which are to be bonded to the microcircuit in use, fusible electrically conductive bonding material which can be fused to effect bonding at a fusion temperature lower than that of the tubular material. An article according to claim 4, characterised in that the fusible material is a solder or similar low-melting-point metal alloy.

Inventors: LUDDEN MICHAEL JOSEPH, NYHOLM PETER, LUDDEN, MICHAEL JOSEPH, NYHOLM, PETER
Applicants: RAYCHEM LTD, RAYCHEM LIMITED
Application year: 1989
Main classification: H01L23
IPC codes: H01L23, G03F7, B23K26, B23K1, B23K31, H01L21, H05K3, H05K1, B23K20