Microelectronic flip chip packages with solder wetting pads and associated methods of manufacturing

Abstract

Processes of assembling microelectronic packages with lead frames and/or other suitable substrates are described herein. In one embodiment, a method for fabricating a semiconductor assembly includes forming an attachment area and a non- attachment area on a lead finger of a lead frame. The attachment area is more wettable to the solder ball than the non-attachment area during reflow. The method also includes contacting a solder ball carried by a semiconductor die with the attachment area of the lead finger, reflowing the solder ball while the solder ball is in contact with the attachment area of the lead finger, and controllably collapsing the solder ball to establish an electrical connection between the semiconductor die and the lead finger of the lead frame.

1 - 23 . (canceled) 
     
     
         24 . A method for fabricating a semiconductor assembly, comprising:
 defining an attachment area and a non-attachment area on a lead finger of a lead frame, wherein said defining creates wettability differential between the attachment area and the non-attachment area;   contacting an electrical coupler of a semiconductor die with the attachment area of the lead finger;   reflowing the electrical coupler while the electrical coupler is in contact with the attachment area of the lead finger; and   controlling an amount of migration in the electrical coupler from the attachment area toward the non-attachment area.   
     
     
         25 . The method of  claim 24 , wherein the defining an attachment area and a non-attachment area comprises screen printing. 
     
     
         26 . The method of  claim 24 , further comprising attaching the electrical coupler to a bump site of the semiconductor die using plating. 
     
     
         27 . The method of  claim 24 , wherein defining the attachment area and the non-attachment area comprises attaching a preform onto the lead finger with an adhesive, the preform having a first portion generally corresponding to the attachment area and a second portion generally corresponding to the non-attachment area. 
     
     
         28 . The method of  claim 24 , further comprising:
 attaching the coupler to a bump site of the semiconductor die prior to contacting the coupler with the attachment area of the lead finger; and   at least partially encapsulating the semiconductor die, the coupler, and the lead finger with an encapsulant.   
     
     
         29 . The method of  claim 24  wherein defining the attachment area and the non-attachment area comprises:
 depositing a masking material on a surface of the lead finger; 
 patterning the masking material to form an opening corresponding to the attachment area, the opening exposing a first portion of the surface of the lead finger, wherein a second portion of the surface is covered by the masking material; 
 depositing a wetting material on the first portion of the surface of the lead finger through the opening in the masking material; 
 removing the masking material from the surface of the lead finger; and 
 treating the second portion of the surface of the lead finger such that the second portion is less wettable to the solder coupler during reflow than the first portion. 
 
     
     
         30 . The method of  claim 24  wherein defining the attachment area and the non-attachment area comprises:
 depositing a photoresist on a surface of the lead finger; 
 patterning the photoresist to form an opening corresponding to the attachment area, the opening exposing a first portion of the surface of the lead finger, wherein a second portion of the surface is covered by the photoresist; 
 depositing a material comprising silver (Ag) on the first portion of the surface of the lead finger through the opening in the photoresist; 
 removing the photoresist from the second portion of the surface of the lead finger; and p 1  oxidizing the second portion of the surface of the lead finger. 
 
     
     
         31 . The method of  claim 24  wherein defining the attachment area and the non-attachment area comprises at least one of:
 depositing a wetting material on a first portion of the lead finger such that the first portion is more wettable to the solder during reflow than the second portion; or 
 treating a second portion of the lead finger such that the second portion is less wettable to the solder during reflow than the first portion. 
 
     
     
         32 . The method of  claim 24  wherein defining the attachment area and the non-attachment area comprises:
 depositing a masking material on a surface of the lead finger; 
 removing a portion of the masking material, a remaining portion of the masking material covering a first portion of the surface of the lead finger, wherein a second portion of the surface of the lead finger is exposed through the masking material; 
 treating the second portion of the surface of the lead finger such that the second portion is less wettable to the solder coupler during reflow than the first portion; and 
 thereafter, removing the remaining portion of the masking material from the lead finger. 
 
     
     
         33 . The method of  claim 24  wherein:
 the attachment area has a first wettability to the coupler during reflow; 
 the non-attachment area has a second wettability to the coupler during reflow; and 
 controlling the amount of migration of the coupler comprises treating at least one of the attachment area or the non-attachment area such that the second wettability is less than the first wettability by a target amount. 
 
     
     
         34 . The method of  claim 33 , wherein
 controlling the amount of migration of the coupler comprises at least one of (a) depositing silver (Ag) onto a first portion of the lead finger or (b) oxidizing a second portion of the lead finger.   
     
     
         35 . The method of  claim 24 , wherein defining the non-attachment area includes allowing the non-attachment area to oxidize. 
     
     
         36 . A flip-chip semiconductor device, comprising:
 a semiconductor die with a bump site;   a lead frame with a lead frame finger having an attachment area and a non-attachment area, the attachment area and non-attachment area having a wettability differential; and   a solder coupler contacting the bump site and the attachment area of the lead frame finger, wherein the migration of the solder coupler has been controlled such that the solder coupler has not substantially migrated onto the non-attachment area.   
     
     
         37 . The flip-chip semiconductor device of  claim 36 , wherein the attachment area of the lead frame finger comprises deposited silver (Ag). 
     
     
         38 . The flip-chip semiconductor device of  claim 36 , wherein the solder coupler has substantially retained its pre-reflow shape. 
     
     
         39 . The flip-chip semiconductor device of  claim 36 , wherein the non-attachment area of the lead frame finger is oxidized. 
     
     
         40 . The flip-chip semiconductor device of  claim 36 , wherein the solder coupler is plated to the semiconductor die bump site. 
     
     
         41 . The flip-chip semiconductor device of  claim 36 , wherein the semiconductor die is disposed over the lead frame in a flip-chip configuration to align the solder coupler between the semiconductor die and the corresponding attachment area on the lead frame. 
     
     
         42 . The flip-chip semiconductor device of  claim 36 , wherein the non-attachment area comprises oxidized metal. 
     
     
         43 . A microelectronic package, comprising:
 a lead frame including lead fingers, each lead finger including a first surface and a second surface;   a contact pad including a wetting material disposed on a portion of the first surface, wherein the contact pad and an area on the first surface adjacent to the contact pad have a wettability differential;   a semiconductor die including bump sites; and   electrical couplers attached to the bump sites of the semiconductor die and the contact pads of the lead fingers, wherein the electrical couplers are confined to the contact pads;   wherein the second surface of the lead finger is configured to interface with an external device.   
     
     
         44 . The microelectronic package of  claim 43 , wherein the wetting material includes a material wettable to the electrical couplers. 
     
     
         45 . The microelectronic package of  claim 44 , wherein the wetting material includes a metal or a metal alloy. 
     
     
         46 . The microelectronic package of  claim 43 , wherein the electrical couplers include a solder material. 
     
     
         47 . The microelectronic package of  claim 46 , wherein the solder material includes a metal alloy. 
     
     
         48 . The microelectronic package of  claim 43 , wherein the electrical couplers are spaced apart. 
     
     
         49 . The microelectronic package of  claim 43 , wherein the semiconductor die is disposed over the lead frame in a flip-chip configuration to align the electrical couplers between the bump sites of the semiconductor die and the corresponding contact pads on the lead fingers. 
     
     
         50 . The microelectronic package of  claim 43 , wherein the area on the first surface adjacent to the contact pad comprises oxidized metal.