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Fluxless assembly of chip size semiconductor packages

  • US 7,098,072 B2
  • Filed: 03/01/2002
  • Issued: 08/29/2006
  • Est. Priority Date: 03/01/2002
  • Status: Expired due to Fees
First Claim
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1. A method for soldering a first substrate (12) to and in electrical connection with a second substrate (18) without using a flux or reducing atmosphere, the method characterized by:

  • forming a first electrically conductive pad (14) on a first surface of the first substrate (12), the first pad including an upper portion comprising at least one component of an electrically conductive eutectic alloy;

    forming a corresponding second pad (16) on a first surface of the second substrate (18), the second pad including an upper portion comprising at least one other component of the eutectic alloy;

    forming at least one sharp upstanding peak (50, 58) on an upper surface of at least one of the first and second pads (14, 16);

    urging the respective first surfaces of the first and second substrates (12, 18) toward each other such that the respective upper surfaces of the first and second pads (14, 16) are brought together in a forceful opposing abutment with each other;

    heating the opposing pads (14, 16) to at least the soldering temperature of the eutectic alloy and until the at least one sharp upstanding peak (50, 58) on the at least one pad penetrates through any oxide films (52) on the respective upper surfaces of the pads and contacts the upper surface of the opposing other pad, thereby initiating melting and dissolution of the respective upper portions of the opposing pads, including the sharp upstanding peaks, into each other; and

    ,cooling the opposing pads to solidify the dissolved, molten upper portions thereof into an electrically conductive joint between the pads; and

    ,wherein forming the at least one sharp peak (50, 58) is characterized by;

    forming a lower portion (42, 44, 46,48) of the at least one pad (14, 16, 20, 22), the lower portion comprising a metal or a semiconductor;

    forming a coating (56) on an upper surface of the lower portion of the at least one pad, the coating consisting of the same at least one eutectic alloy component comprising the upper portion of the at least one pad; and

    ,forming the at least one peak (50, 58) on an upper surface of the coating (56), the at least one peak consisting of the same at least one eutectic alloy component comprising the upper portion of the at least one pad.

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