SUBSTRATE WITH BOND FINGERS
A flip chip mounting board includes a substrate having a top surface and a plurality of generally parallel, longitudinally extending, laterally spaced apart bond fingers are formed on the top surface. Each of the plurality of bond fingers has a first longitudinal end portion and a second longitudinal end portion. A first strip of laterally extending solder resist material overlies the first longitudinal end portions of the bond fingers. The first strip has an edge wall with a plurality of longitudinally projecting tooth portions separated by gaps with a longitudinally extending tooth portion being aligned with every other one of the bond fingers. Adjacent bond fingers have first end portions covered by different longitudinal lengths of solder resist material.
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During the past decade flip chip technology has emerged as a popular alternative to wire bonding for interconnecting semiconductor devices such as integrated circuit (IC) dies to substrates such as printed circuit boards, carrier substrates, interposers and other dies.
“Flip chip,” is also known as “controlled collapse chip connection” or its acronym, “C4.” With flip chip technology, solder balls/bumps are attached to electrical contact pads on one face of a die/chip. The flip chip dies are usually processed at the wafer level, i.e., while multiple identical dies are still part of a large “wafer.” Solder balls are deposited on chip pads on the top side of the wafer. The wafer is sometimes “singulated” or “diced” (cut up into separate dies) at this point to provide a number of separate flip chip dies each having solder balls on the top face surface. The chips may then be “flipped” over to connect the solder balls to matching contact pads on the top surface of a substrate such as a printed circuit board or carrier substrate on which the flip chip is mounted. Solder ball attachment is usually provided by reflow heating.
As IC dies have become more complex, the number of solder bumps/balls on flip chips have increased dramatically. Whereas in the past the solder balls were usually provided by relatively large round solder balls attached to the chip contact pads, more recently copper pillars (“CuP's”) have been used in place of the solder balls. A CuP is an elongated copper post member that is attached at one end to a contact pad on the flip chip die. The CuP extends outwardly from the die in a direction perpendicular to the face of the die. Each CuP has a generally bullet or hemisphere shaped solder piece attached to its distal end. The CuP's are bonded by this solder piece to corresponding contact pads on a substrate as by reflow heating. CuP's are capable of being positioned much more densely, i.e., at a “higher pitch,” than conventional solder balls/bumps. One manner of facilitating connection of a substrate to a die having such high CuP density is to provide bond fingers, rather than conventional contact pads, on the substrate to which the flip chip is to be mounted. The bond fingers are elongated contact pads that may be positioned in close parallel relationship without any insulating material between them.
This specification, in general, discloses a flip chip mounting board that comprises a substrate 120 with a top surface 121,
This specification also discloses a method of making a flip chip assembly. This method, in general, includes forming a plurality of laterally spaced apart, longitudinally extending bond fingers 122, 124, etc., on a surface 121 of a substrate 120. The method also includes applying a transversely extending solder resist layer or strip 142 over first end portions 132 of the plurality of bond fingers 122, 124, etc. The solder resist strip 142 if formed with an edge wall 146 including a plurality of longitudinally extending tooth portions 152 separated by gaps 153, with each tooth portion 152 and each gap 153 aligned with a different one of the bond fingers 122, 124, etc. in each adjacent pair of bond fingers, e.g. 122, 124. Having thus generally described an embodiment of a flip chip mounting board and an embodiment of a method of making a flip chip assembly, these and other embodiments will now be described in detail.
As illustrated by
A conventional process by which a flip chip die 10 with copper post connectors 18 is mounted on a substrate 30 is illustrated in
In the embodiment illustrated in
In another embodiment illustrated in
Solder resist strip edge walls having the various shapes described herein and other shapes may be formed by screen printing the solder resist strips in such shapes. Solder resist screen printing is known in the art.
Although certain specific embodiments of a flip chip mounting board and a flip chip assembly and a method of making a flip chip assembly have been described in detail herein, various modification of such apparatus and method will be obvious to persons skilled in the art after reading this disclosure. It is intended that the appended claims be broadly construed so as to encompass such alternative embodiments, except to the extent limited by the prior art.
Claims
1. A flip chip mounting board comprising:
- a substrate having a top surface;
- a plurality of generally parallel, longitudinally extending, laterally spaced apart bond fingers formed on said top surface, each of said plurality of bond fingers having a first longitudinal end portion and a second longitudinal end portion; and
- a first strip of laterally extending solder resist material overlying said first longitudinal end portions of said bond fingers, said first strip comprising an edge wall having a plurality of longitudinally projecting tooth portions separated by gaps with a longitudinally extending tooth portion being aligned with every other one of said bond fingers whereby adjacent ones of said bond fingers have first end portions covered by different longitudinal lengths of solder resist material.
2. The flip chip mounting board of claim 1 wherein said longitudinally projecting tooth portions have generally straight edged rectangular tooth shapes.
3. The flip chip mounting board of claim 1 wherein said longitudinally projecting tooth portions have generally rounded edged rectangular tooth shapes.
4. The flip chip mounting board of claim 1 wherein said longitudinally projecting tooth portions have generally straight edged triangular tooth shapes.
5. The flip chip mounting board of claim 1, further comprising a second strip of laterally extending solder resist material overlying said second longitudinal end portions of said bond fingers, said second strip comprising an edge wall having a plurality of longitudinally projecting tooth portions separated by gaps that overlies said second end portions of said plurality of bond fingers with a longitudinally extending tooth portion being aligned with every other one of said bond fingers, whereby adjacent ones of said bond fingers have second end portions covered by different longitudinal lengths of solder resist material.
6. The flip chip mounting board of claim 5 wherein tooth portions of said first solder resist strip are aligned with gaps in said edge wall of said second solder resist strip.
7. The flip chip mounting board of claim 7 wherein tooth portions of said first solder resist strip overlap with tooth portions of said second solder resist strip.
8. The flip chip mounting board of claim 1 each longitudinally extending tooth portion of said edge wall having a proximal end, and further comprising a layer of nonconductive paste (NCP) overlying said first strip of solder resist material except for said longitudinally projecting tooth portions thereof whereby overrun from said NCP layer onto said plurality of bond fingers is substantially confined to portions of said bond fingers located in said gaps between said tooth portions.
9. A flip chip assembly comprising:
- a flip chip mounting board comprising: a substrate having a top surface; a plurality of generally parallel, longitudinally extending, laterally spaced apart bond fingers formed on said top surface, each of said plurality of bond finger having a first longitudinal end portion and a second longitudinal end portion; a first strip of laterally extending solder resist material overlying said first longitudinal end portions of said bond fingers, said first strip comprising an edge wall having a plurality of longitudinally projecting tooth portions separated by gaps, with a longitudinally extending tooth portion being aligned with every other one of said bond fingers, whereby adjacent ones of said bond fingers have first end portions covered by different longitudinal lengths of solder resist material; and a flip chip die having a plurality of solder tipped copper pillar conductors mounted on said flip chip mounting board with said plurality of solder tipped copper pillar conductors bonded to said bond fingers on said flip chip mounting board.
10. The flip chip assembly of claim 9 wherein said flip chip mounting board comprises one of an interposer and a chip carrier.
11. The flip chip assembly of claim 9 wherein said flip chip mounting board comprises a printed circuit board.
12. A method of making a flip chip assembly comprising:
- forming a plurality of laterally spaced apart, longitudinally extending bond fingers on a surface of an organic substrate; and
- applying a transversely extending solder resist strip over first end portions of the plurality of bond fingers, the solder resist strip having an edge wall comprising a plurality of tooth portions separated by gaps, with each tooth portion and each gap aligned with a different one of the bond fingers in each adjacent pair of bond fingers.
13. The method of claim 12 further comprising:
- connecting a plurality of solder tipped copper pillar connectors on a flip chip die with the plurality of longitudinally extending bond fingers on the surface of the substrate.
14. The method of claim 12 further comprising:
- applying a layer of nonconductive paste to an area of the solder resist layer that excludes the tooth portions thereof;
- positioning a plurality of solder tipped copper pillar connectors on a flip chip die over the plurality of longitudinally extending bond fingers on the surface of the substrate;
- moving the flip chip die into contact with the layer of nonconductive paste; and
- using thermal compressive bonding to attach the solder tipped copper pillar connectors to the bond fingers.
15. The method of claim 12 wherein said applying a transversely extending solder resist layer comprises making the width of each generally tooth shaped portion at its proximal end approximately the same as the width of an aligned bond finger added to the width of the gap between adjacent bond fingers.
16. The method of claim 12 wherein said applying a transversely extending solder resist layer over first end portions of the plurality of bond fingers, the solder resist layer having an edge wall comprising a plurality of generally rectangular tooth shaped portions separated by rectangular voids, with each tooth shaped portion and each void aligned with a different one of each adjacent pair of said plurality of bond fingers.
17. The method of claim 16 wherein said applying a transversely extending solder resist layer comprises providing a solder resist layer having an edge wall comprising a plurality of generally rectangular tooth shaped portions having linear sides and right angle corners.
18. The method of claim 16 wherein said applying a transversely extending solder resist layer comprises providing a solder resist layer having an edge wall comprising a plurality of generally rectangular tooth shaped portions having curved sides and rounded corners.
19. The method of claim 12 wherein said applying a transversely extending solder resist layer over first end portions of the plurality of bond fingers comprises applying a solder resist layer having an edge wall comprising a plurality of generally triangular tooth shaped portions separated by triangular voids.
20. The method of claim 12 further comprising applying a second transversely extending solder resist strip over second end portions of the plurality of bond fingers, the second solder resist strip having an edge wall comprising a plurality of tooth portions separated by gaps, with the tooth portion in the second solder resist strip aligned with gaps in the first solder resist strip.
Type: Application
Filed: Jan 16, 2013
Publication Date: Jul 17, 2014
Applicant: Texas Instruments Incorporated (Dallas, TX)
Inventors: Raymond Maldan Partosa (Baguio City), Jesus Bajo Bautista, JR. (Baguio City), James Raymond Baello (Baguio City), Roxanna Bauzon Samson (Benguet)
Application Number: 13/743,213
International Classification: H01L 23/498 (20060101); H01L 23/00 (20060101);