 |
Claims  |
|
|
I claim:
1. A method for mounting a protuberant conductive contact to a conductive terminal on an electronic component, the method comprising the sequential steps of:
providing a wire having a continuous feed end,
intimately bonding the feed end to the terminal,
forming from the bonded feed end a stem which protrudes from the terminal and has a first stem end thereat,
bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
severing the stem at the second stem end to define a skeleton,
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component,
eliminating the sacrificial member.
2. The method as claimed in claim 1, wherein during the eliminating step the second stem ends are severed from the sacrificial member.
3. The method as claimed in claim 1, performed on a plurality of wires on a plurality of the terminals on the electronic component.
4. The method as claimed in claim 1, wherein:
the bonding is performed by applying at least one of a group consisting of superambient pressure, superambient temperature and ultrasonic energy.
5. The method as claimed in claim 1, wherein:
the severing of the second end is performed by melting the wire.
6. The method as claimed in claim 1, wherein:
the forming steps and the severing steps are performed by a wirebonding apparatus, and
after the severing steps but before the depositing step, shaping the skeleton by means of a tool external to the apparatus.
7. The method as claimed in claim 1, wherein:
the severing of the second end is performed by mechanical shearing.
8. The method as claimed in claim 1, wherein:
the stem has a shape; and
further comprising:
during the forming step, the shape of the stems is determined by means of a software algorithm in a control system of an automated wirebonding apparatus.
9. The method as claimed in claim 1, wherein:
the deposition is performed by means of electrochemical plating in an ionic solution.
10. The method as claimed in claim 1, wherein:
the conductive material enveloping the skeleton and at least the adjacent surface of the component comprises a plurality of dissimilar layers.
11. Method, as set forth in claim 1, wherein:
the conductive material is deposited by an electroless plating process.
12. Method, as set forth in claim 1, further comprising:
during deposition of the conductive material, causing a compressive internal stress in the conductive material.
13. The method, as claimed in claim 1, wherein:
the cross-sectional area of the wire is rectangular.
14. The method as claimed in claim 1, wherein:
the wire is made of a metal selected from a group consisting of gold, silver, beryllium, copper, aluminum, rhodium, ruthenium, palladium, platinum, cadmium, tin, lead, indium, antimony, phosphorous, boron, nickel, magnesium, and their alloys, and
the conductive material is deposited as a plurality of layers, and at least one of the layers of the conductive material is a metal selected from a group consisting of nickel, phosphorous, boron, cobalt, iron, chromium, copper, zinc, tungsten,
tin, lead, bismuth, indium, cadmium, antimony, gold, silver, rhodium, palladium, ruthenium, and their alloys.
15. The method as claimed in claim 1, wherein:
the wire is made of a metal selected from a group consisting of gold, silver, beryllium, copper, aluminum, rhodium, ruthenium, palladium, platinum, cadmium, tin, lead, indium, antimony, phosphorous, boron, nickel, magnesium, and their alloys.
16. The method as claimed in claim 1, wherein:
the conductive material is deposited as a plurality of layers, and at least one of the layers of the conductive material is a metal selected from a group consisting of nickel, phosphorous, boron, cobalt, iron, chromium, copper, zinc, tungsten,
tin, lead, bismuth, indium, cadmium, antimony, gold, silver, rhodium, palladium, ruthenium, and their alloys.
17. A method, according to claim 1, further comprising:
performing the method on at least one terminal on an electronic component, wherein:
the wire is made primarily of a metal selected from a group consisting of gold, copper, aluminum, silver, lead, tin, indium and their alloys;
the skeleton is coated with a first layer of the conductive material selected from a group consisting of nickel, cobalt, boron, phosphorous, copper, tungsten, titanium, chromium, and their alloys;
a top layer of the conductive material is solder selected from a group consisting of lead, tin, indium, bismuth, antimony, gold, silver, cadmium and alloys thereof and their alloys.
18. The method as claimed in claim 1, wherein:
each of two surfaces of the electronic component has at least one protuberant contact mounted thereto.
19. The method as claimed in claim 1, wherein:
the wire stem is S-shaped.
20. Method, according to claim 1, wherein:
the stem has a length; and
the conductive coating covers the entire length of the stem.
21. Method, according to claim 1, wherein:
the conductive material is applied in multiple coating layers; and
at least one of the multiple coating layers is deposited along the entire length of the stem.
22. Method, according to claim 1, wherein:
the stem has a length; and
the conductive material covers only a portion of the length of the stem.
23. Method, according to claim 1, further comprising:
supplying the wire from a spool of wire.
24. Method, according to claim 1, wherein:
the electronic component is an interconnection substrate.
25. Method, according to claim 1, wherein:
the electronic component is an interconnect socket.
26. Method, according to claim 1, wherein:
the electronic component is a test socket.
27. Method, according to claim 1, wherein:
the electronic component is a semiconductor wafer.
28. Method, according to claim 1, wherein:
the electronic component is a ceramic semiconductor package.
29. Method, according to claim 1, wherein:
the electronic component is a plastic semiconductor package.
30. Method, according to claim 1, wherein:
the stem is bonded to the surface of the electronic component using ultrasonic bonding equipment.
31. Method, according to claim 1, wherein:
the wire is bonded to the surface of the electronic component using thermosonic bonding equipment.
32. Method, according to claim 1, wherein:
the wire is bonded to the surface of the electronic component using thermocompression bonding equipment.
33. Method, according to claim 1, wherein wirebonding equipment is used to bond the feed end of the wire to a surface of the electronic component, and further comprising:
during forming, controlling all aspects of geometric characteristics of the stem with a specific set of commands entered into an electronic control system of the wirebonding equipment.
34. Method, according to claim 1, wherein:
an end of the wire which is opposite the feed end of the wire is a free end; and
automated wirebonding equipment, controllable by a software algorithm, is used to form the stem and to determine a coordinate of a tip of its free end.
35. Method, according to claim 1, further comprising:
forming the stem with automated equipment controlled by a control system, according to a set of specified parameters.
36. Method, according to claim 1, wherein:
the conductive material is deposited by a process selected from the group consisting of physical vapor deposition and chemical vapor deposition.
37. Method, according to claim 1, wherein:
the conductive material is deposited by a process that involves the decomposition of gaseous, liquid or solid precursors.
38. Method, according to claim 1, wherein:
the conductive material has a tensile strength in excess of 80,000 pounds per square inch.
39. Method, according to claim 1, wherein:
the conductive contact has controlled characteristics selected from the group consisting of physical properties, metallurgical properties, mechanical properties, bulk and surface.
40. Method, according to claim 1, further comprising:
bonding, shaping and severing a plurality of stems, a first portion of the stems originating from a first level of the electronic component, a second portion of the stems originating from a second level of the electronic component, said first
level and said second level being non-coplanar with one another;
wherein:
the free ends of said plurality of stems are severed to be substantially coplanar with one another.
41. Method, according to claim 1, wherein:
a plurality of stems are arranged in an array pattern on a surface of the electronic component.
42. The method as claimed in claim 1, performed on a plurality of the terminals on the electronic component.
43. The method as claimed in claim 42, performed on a plurality of wires on a plurality of the terminals on the electronic component.
44. The method as claimed in claim 42, wherein:
the conductive material enveloping the skeleton and at least the adjacent surface of the component comprises a plurality of layers.
45. The method as claimed in claim 42, wherein:
the deposition is performed by means of electrochemical plating in an ionic solution.
46. The method as claimed in claim 42, wherein the conductive material is reactive with the wire stem; and further comprising:
a barrier layer which is not reactive with the wire stem disposed between the wire stem and the conductive material.
47. The method as claimed in claim 1, performed on a plurality of the terminals, wherein a shape of the skeleton and mechanical properties of the conductive material are organized collectively to impart resilience to the protuberant conductive
contact.
48. The method as claimed in claim 47, wherein the conductive material is reactive with the wire stem; and further comprising:
a barrier layer which is not reactive with the wire stem disposed between the wire stem and the conductive material.
49. The method as claimed in claim 1, wherein:
the conductive material enveloping the skeleton and at least the adjacent surface of the component comprises a plurality of dissimilar layers.
50. The method as claimed in claim 49, wherein the conductive material is reactive with the wire stem; and further comprising:
a barrier layer which is not reactive with the wire stem disposed between the wire stem and the conductive material.
51. The method as claimed in claim 1, wherein the conductive material is reactive with the wire stem; and further comprising:
a barrier layer which is not reactive with the wire stem disposed between the wire stem and the conductive material.
52. The method as claimed in claim 51, wherein the wire is gold and the conductive layer contains tin.
53. Method, according to claim 1, wherein:
the wire has a diameter between 0.0005 and 0.005 inches.
54. Method, according to claim 53, wherein:
the wire has a diameter between 0.0007 and 0.003 inches.
55. Method, according to claim 1, wherein:
the conductive material is deposited to a thickness between 0.00005 and 0.007 inches.
56. Method, according to claim 55, wherein:
the conductive material is deposited to a thickness between 0.00010 and 0.003 inches.
57. Method, according to claim 1, wherein:
the wire has a diameter between 0.0005 and 0.005 inches; and
further comprising:
prior to depositing the conductive material, coating the stem with nickel having a thickness between 0.00005 and 0.007 inches.
58. Method, according to claim 57, wherein:
the stem has a diameter between 0.0007 and 0.003 inches; and
the nickel has a thickness between 0.00010 and 0.003 inches.
59. Method, according to claim 1, wherein:
the electronic component is a semiconductor device.
60. Method, according to claim 59, wherein:
the semiconductor device is a silicon device.
61. Method, according to claim 59, wherein:
the semiconductor device is a gallium arsenide device.
62. A method for mounting a protuberant conductive contact to a conductive terminal on an electronic component, the method comprising the sequential steps of:
providing a wire having a continuous feed end,
intimately bonding the feed end to the terminal,
forming from the bonded feed end a stem which protrudes from the terminal and has a first stem end thereat,
bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
severing the stem at the second stem end to define a skeleton,
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component, and
eliminating the sacrificial member,
further comprising:
performing the method on a plurality of the terminals, wherein a shape of the skeleton and mechanical properties of the conductive material are organized collectively to impart resilience to the protuberant conductive contact;
wherein the conductive material is provided with a multitude of microprotrusions on its surface.
63. A method for mounting a conductive contact to a conductive terminal on an electronic component, the method comprising the steps of:
first, providing a wire having a continuous feed end, and bonding the feed end to the terminal,
after bonding the feed end, forming, from the bonded feed end, a stem which protrudes from the terminal, said stem having a first stem end which is the bonded feed end,
after forming the stem, bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
after bonding the second stem end, severing the stem at the second stem end to define a skeleton, and
further comprising:
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component,
eliminating the sacrificial member.
64. A method for mounting a conductive contact to a conductive terminal on an electronic component, the method comprising the sequential steps of:
providing a wire having a continuous feed end,
bonding the feed end to a sacrificial member;
forming from the bonded feed end a stem which protrudes from the component, said stem having a first stem end which is the bonded feed end and a second stem end at an opposite end of the stem;
bonding the second stem end to a terminal on the electronic component;
severing the stem at the second stem end to define a skeleton,
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component, and
eliminating the sacrificial member.
65. A method for mounting a conductive contact to an area on a surface of an electronic component, the method comprising the steps of:
providing a wire having a continuous feed end,
bonding the feed end to the terminal,
forming, from the bonded feed end, a stem which protrudes from the terminal, said stem having a first stem end which is the bonded feed end,
bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
severing the stem at the second stem end to define a skeleton,
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component,
eliminating the sacrificial member.
66. A method for mounting a conductive contact to an area on a surface of an electronic component, the method comprising the steps of:
providing a wire having a continuous feed end,
bonding the feed end to the terminal,
forming, from the bonded feed end, a stem which protrudes from the terminal said stem having a first stem end which is the bonded feed end,
bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
severing the stem at the second stem end to define a skeleton,
eliminating the sacrificial member; and
after eliminating the sacrificial member, depositing a conductive material to envelop the skeleton and at least adjacent surface of the component.
67. A method for mounting a protuberant conductive contact to a conductive terminal on an electronic component, the method comprising the sequential steps of:
providing a wire having a continuous feed end,
intimately bonding the feed end to the terminal,
forming from the bonded feed end a stem which protrudes from the terminal and has a first stem end thereat,
bonding a second stem end to a sacrificial member mounted in spaced relationship from the component,
severing the stem at the second stem end to define a skeleton,
depositing a conductive material to envelop the skeleton and at least adjacent surface of the component, and
eliminating the sacrificial member,
further comprising:
performing the method on a plurality of the terminals, wherein a shape of the skeleton and mechanical properties of the conductive material are organized collectively to impart resilience to the protuberant conductive contact;
wherein the depositing step includes placement of a plurality of layers each differing from one another.
68. The method as claimed in claim 67, wherein at least one of the layers comprising conductive material has a jagged topography in order to reduce contact resistance of the protuberant conductive contact when mated to a matching terminal.
69. The method as claimed in claim 67, wherein the conductive material is reactive with the wire stem; and further comprising:
a barrier layer which is not reactive with the wire stem disposed between the wire stem and the conductive material. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
This invention relates in general to electronic assemblies and testing thereof. In particular, the invention relates to a method of manufacture of protruding, controlled aspect ratio and shape contacts for uses in interconnections of assemblies
and testing thereof.
Interconnections which involve protruding electrical contacts are used extensively in packaging of electronics. Pin grid array packages, both plastic and ceramic, housing a variety of semiconductors, use area arrays of pins as interconnect
contacts for connection to circuit boards. Pins can be attached to their receiving package conductors by use of a variety of methods. For ceramic packages, pins are inserted into non-reacting brazing fixtures and are then gang-brazed to corresponding
conductive terminals on the package. This approach is characterized by significant non-recurring engineering costs and lead times involved in production of the brazing fixture. Plastic pin grid array packages most commonly use pins which are inserted
into metallized through holes in a circuit board, while the dimensions of pins and the holes normally chosen to facilitate good contact between the walls of the pins and the coating of the holes. This approach has a disadvantage in that the coated holes
and the pins block some circuit routing channels within the circuit board, thus forcing either use of narrow circuit traces, or increase in circuit board area, either of which results in increased costs.
Permanent connection of the pin grid array packages to circuit boards often is accomplished by inserting pins through corresponding holes in a circuit board, the pins protruding to a predetermined length beyond the circuit board. A resulting
assembly then is passed through a wave soldering machine, and the pin grid array thus is soldered to the circuit board. Alternatively, a pin grid array can be inserted into a low insertion force or zero insertion force socket for a demountable assembly. Such a socket, in its turn, normally is connected permanently to a board.
A current trend in interconnections is toward face-to-face surface mounting of components to boards and semiconductor chips to substrates. This approach is best accomplished with protruding contact structures on top of (or otherwise protruding
from) contact carrying conductive terminals or traces. Conductive terminal arrangements on facing components and substrates are increasingly being made of the area array type, as this allows for larger contact-to-contact separation as compared with
components characterized by peripheral arrangement of interconnection contacts.
Pins attached to either ceramic or plastic packages according to the traditional methods are, in general, not appropriate for mounting to patterns of surface contacts on circuit boards, due to pin length variation. For surface mounting, the pins
would have to be planarized, which represents an additional expensive step subsequent to pin assembly. In addition, there is a significant cost penalty associated with production of pin-carrying packages with pin-to-pin separations of 50 mils, or lower.
There is currently an increasing need for a low cost method of attaching protruding contacts from conductive terminals, arising from proliferation of surface mountable area array contact packages. Stand-off height of protruding contacts is
particularly important when coefficients of thermal expansion of components and of circuit board materials differ significantly. The same is true for attachment of un-packaged semiconductor chips to interconnection substrates. These expansive concerns
call for a low cost, high volume method of manufacturing protruding, controlled aspect ratio or shape electrical contacts on top of (or otherwise protruding from) contact carrying conductive terminals, on top of any device or circuit bearing substrate,
board material or component, and its applications to surface mount interconnections of devices, components and substrates.
THE PRIOR ART
U.S. Pat. Nos. 5,189,507, 5,095,187 and 4,955,523 disclose a method of manufacturing of controlled height protruding contacts in a shape of wires for direct soldering to a mating substrate. The wires are bonded to terminals without use of any
material other than that of wire and the terminals, using ultrasonic wirebonding methods and equipment, which comprises a standard industry technique for interconnecting semiconductor chips to packages. The patents also describe a bonding head which
incorporates a wire weakening means for controlling length of free standing severed wires. Vertically free standing wires present a handling problem during assembly, which is addressed in the patents by providing for polymer encapsulation of bonds
between the wires and terminals. The polymer coating, which is optional, also compensates for another disadvantage of the approach, namely weak points along the wire, typically the point of contact between the wire and terminal metallization, and in
case of ball bonding, in a heat effected zone of the wire just above impression of a bonding capillary. While these patents provide for controlled height contacts, and discuss 2 d to 20 d aspect ratios, in practice they do not assume controlled aspect
ratios for all kinds of protruding contacts which are required in various applications. For instance, standard, high speed wirebonding equipment could not handle a 30 mil diameter wire. Therefore, according to these inventions, a 30 mil diameter, 100
mil high contact could only be produced on lower throughput specialized equipment, at higher cost. In addition, a gold wire as described in a preferred embodiment, would have a problem of dissolving in solder during a soldering cycle, which causes long
term reliability problems with solder joints. Similarly, direct soldering of copper contacts would in many cases result in undesirable reaction between copper and solder at elevated temperatures. While nickel metal is the material of choice for solder
joint reliability, nickel wire can not be used for ultrasonic wirebonding to metal terminals due to its high mechanical strength and passivating, oxide forming properties. Chemical, physical and mechanical properties, as well as permissible dimensions
and shapes of the protuberant contacts produced according to this invention are limited to the capabilities and materials choices compatible with known wire bonding techniques.
U.S. Pat. No. 3,373,481 describes a method of interconnecting semiconductor components on substrates by means of dissolving protruding gold projections on the components in solder masses formed on the substrate terminals. The gold projections
are formed by compression and extrusion of gold balls against the terminals. This approach is incapable of producing high aspect ratio protruding contacts because of limitations of the extrusion method. In addition, dissolution of gold in solder, as
taught by this approach creates a problem due to reliability concerns. The method also limits selection of contact material to easily extrudable metals, like gold.
There are several methods in the prior art for controlled elongation of solder masses between a component and a substrate. The goal is to create a column-like solder shape, preferably an ho | | |
