Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Ball or nail head type contact – lead – or bond
Patent
1996-06-19
1998-09-01
Saadat, Mahshid D.
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Ball or nail head type contact, lead, or bond
257781, 257779, H01L 2348, H01L 2352
Patent
active
058014497
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The invention relates to a process and a substrate for connecting an integrated circuit to another substrate by means of balls. More specifically, the invention relates to a connecting substrate of an integrated circuit comprising an insulating film, one side of which carries conductors and the other side of which carries balls connected to the respective conductors by means of via holes recessed into the film. Another subject of the invention is an integrated circuit package. The invention advantageously applies to the technology of connection by means of an array of balls, commonly called BGA (Ball Grid Array) technology, and more specifically to that known as tape or TBGA (Tape BGA) technology.
DESCRIPTION OF RELATED ART
In the connecting substrate ordinarily used, via holes recessed into a film are metalized and each of them has a metalized ring on the side of the film opposite that which carries the conductors. A connecting ball is fixed to the ring. In order for the ball to be properly supported on the ring, the via hole has a section which is somewhat smaller than that of the ball. The drawback of this connection is that it necessitates the metalization of the via holes, which requires several operations and adds appreciably to the cost of manufacturing the substrate. On the other hand, the small section of the metalized via holes has a relatively high self-induction for the signals and a non-negligible resistance to the passage of the supply currents.
On the other hand, the side which carries the balls of a conventional substrate often carries a conductive metallic foil which serves as a ground plate. This foil is connected to the metalized edges of the via holes intended for the ground leads carried on the other side of the substrate. Of course, the foil is pierced with holes which surround the metalized edges of the other via holes so as to be electrically insulated from them and from the respective balls. However, it is necessary to prevent the solder of these balls from spreading, for example by leaking, to the edges of the holes of the ground foil. Such spreading would create a short-circuit, which would be difficult to repair and would require the substrate, or even the very costly package, to be removed. Moreover, it is also necessary to prevent the solder from spreading near the edges of the holes in the foil in order to eliminate any risk of short-circuit. In order to satisfy these requirements, the balls are made from a material which does not remelt, i.e., reflow, when they are mounted on the film and does not remelt when they are mounted on the board. For this reason, the balls basically retain their dimensions after soldering. There are still other reasons why non-reflow soldering balls are currently used.
However, the use of non-reflow soldering balls entails other drawbacks. In fact, these balls serve to fix the connecting substrate of the integrated circuit to another connecting substrate, such as a printed circuit board for interconnecting several integrated circuits. The balls are therefore connected to connecting pads disposed in coplanar fashion on one side of the board, in a mount known as a surface mount and commonly called CMS (components mounted on the surface) or SMT (Surface Mount Technology). The use of non-reflow soldering balls therefore requires that the connecting pads practically all be in the same plane in order to ensure effective, reliable contact with the respective balls. In other words, the use of non-remeltable balls requires the use of boards which have very strict margins of tolerance for flatness. Add to this limitation of the application of the conventional substrate to boards of this type the drawback of the sharply higher cost of these boards. Moreover, the balls must have very precise dimensions and they are mounted on a film which does not normally have proper flatness. It follows that the apexes of the balls have difficulty remaining within the margins of flatness required for an effective and reliable connection o
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Dehaine Gerard
Stricot Yves
Bull S.A.
Clark S. V.
Kondracki Edward J.
Saadat Mahshid D.
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