U.S. patent application number 09/730229 was filed with the patent office on 2001-09-27 for contact sheet.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Ochiai, Toshimasa.
Application Number | 20010024892 09/730229 |
Document ID | / |
Family ID | 46257691 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024892 |
Kind Code |
A1 |
Ochiai, Toshimasa |
September 27, 2001 |
Contact sheet
Abstract
A contact sheet used with a socket for connecting an integrated
circuit having spherical terminals to a board includes: protruding
contact springs in some or all of numerous through holes provided
in a sheet composed of an insulative elastic material, wherein each
of the contact springs is composed of a conductive material and
constituted by two or more cantilevers fixed onto the sheet by
bonding at one end thereof; the each cantilever has a lower
supporting portion and a spherical terminal holding portion; the
lower supporting portion is composed of or a planar portion formed
adjacently to a portion fixed to the sheet; the spherical terminal
holding portion is formed by vertically or aslant bending the other
end of the cantilever toward one of two openings of a through hole;
and when the integrated circuit is mounted, the spherical terminal
enters into a gap at the spherical terminal holding portion of the
two or more cantilevers to cause the spherical terminal holding
portions of said two or more cantilevers are pushed and spread in a
direction away from the portion of each cantilever that is fixed to
the sheet, and at the same time, pressed against the board.
According to this contact sheet, oxide films are removed and
reliable electrical conduction can be secured without crushing
distal end portions of spherical terminals. Since current passing
distances in contact springs are shorter, the contact sheets can be
ideally used for high-frequency test boards or mounting boards.
Inventors: |
Ochiai, Toshimasa; (Nagoya,
JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
|
Family ID: |
46257691 |
Appl. No.: |
09/730229 |
Filed: |
April 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09730229 |
Apr 16, 2001 |
|
|
|
09410377 |
Sep 30, 1999 |
|
|
|
Current U.S.
Class: |
439/67 |
Current CPC
Class: |
H01R 12/7094 20130101;
G01R 1/0466 20130101; G01R 1/045 20130101; G01R 1/0483 20130101;
H05K 7/1069 20130101; H01R 12/57 20130101; G01R 1/06727
20130101 |
Class at
Publication: |
439/67 |
International
Class: |
H05K 001/00; H01R
012/00 |
Claims
What is claimed is:
1. A contact sheet used with a socket for connecting an integrated
circuit having spherical terminals to a board, comprising:
protruding contact springs in some or all of numerous through holes
provided in a sheet composed of an insulative elastic material,
wherein; each of said contact springs is composed of a conductive
material having two terminals and constituted by electrically
isotopic, facing two or more cantilevers fixed onto said sheet by
bonding at one end thereof; said each cantilever has a lower
supporting portion and a spherical terminal holding portion; said
lower supporting portion is composed of or a planar portion formed
adjacently to a portion fixed to said sheet; said spherical
terminal holding portion is formed by vertically or aslant bending
the other end of said cantilever toward one of two openings of a
through hole; and when said integrated circuit is mounted, said
spherical terminal enters into a gap at the spherical terminal
holding portion of said facing two or more cantilevers to cause the
spherical terminal holding portions of said two or more cantilevers
are pushed and spread in a direction away from the portion of each
cantilever that is fixed to the sheet, and at the same time, a
boundary portion between the spherical terminal holding portions
and the lower supporting portion is pressed against the board.
2. A contact sheet according to claim 1, wherein each contact
spring is composed of three cantilevers, said three cantilevers are
disposed virtually parallel to each other in said through hole, and
two cantilevers on both ends of said three cantilevers and one
cantilever in the middle are fixed to edges of said through hole
that oppose each other.
3. A contact sheet used with a socket for connecting an integrated
circuit having spherical terminals to a board, comprising:
protruding contact springs in some or all of numerous through holes
provided in a sheet composed of an insulative elastic material,
wherein; each of said contact springs is constituted by two or more
cantilevers composed of a conductive material having two terminals,
and said two or more cantilevers are respectively fixed to
adjoining edges of said through hole at one end thereof so that
they are oriented in parallel to each other; each cantilever has a
lower supporting portion and a spherical terminal holding portion;
said lower supporting portion is composed of a planar portion
formed adjacently to a portion fixed to said sheet; said spherical
terminal holding portion is formed by vertically or aslant bending
the other ends of said two or more cantilevers toward one of two
openings of a through hole; dispositions of said two or more
cantilevers installed in a through hole of an arbitrary one column
and dispositions of said two cantilevers installed in a through
hole of another column adjacent to said one column have a point
symmetrical relationship; and when the integrated circuit is
mounted, said spherical terminals of each column push and bent said
two or more cantilevers in a direction away from the portion of
each cantilever that is fixed to said sheet to be well-balanced and
press the cantilevers against the board.
4. A contact sheet according to claim 2, wherein each cantilever is
disposed such that it is parallel to a direction of a column to
which a through hole wherein said cantilever is installed
belongs.
5. A contact sheet according to claim 3, wherein each cantilever is
disposed such that it is parallel to a direction of a column to
which a through hole wherein said cantilever is installed
belongs.
6. A contact sheet according to claim 3, wherein each contact
spring is composed of two or more cantilevers, two cantilevers are
disposed parallel to each other in said through hole, and two
cantilevers are fixed to edges of the through hole that oppose each
other thereby to minimize a pressing force applied when an
integrated circuit is mounted thereon.
7. A contact sheet according to claim 1, wherein each contact
spring is composed of two or more cantilevers, the two or more
cantilevers are disposed parallel to one another in said through
hole, and a bridge connecting the lower supporting portion of the
two or more cantilevers fixed to edges of the through holes
adjacent to each other among the two or more cantilevers is
provided.
8. A contact sheet according to claim 3, wherein each contact
spring is composed of two or more cantilevers, the two or more
cantilevers are disposed parallel to one another in said through
hole, and a bridge connecting the lower supporting portion of the
two or more cantilevers fixed to edges of the through holes
adjacent to each other among the two or more cantilevers is
provided.
9. A contact sheet according to claim 1, said cantilevers are in
contact with the board before the integrated circuit is
mounted.
10. A contact sheet according to claim 3, wherein said cantilevers
are in contact with the board before the integrated circuit is
mounted.
11. A contact sheet according to claim 1, wherein two contact
sheets are unitarily formed via an adhesive sheet having through
holes with the same pattern as the contact sheets, and each of the
two contact sheets has the same number of contact springs on both
sides of the adhesive sheet.
12. A contact sheet according to claim 3, wherein two contact
sheets are unitarily formed via an adhesive sheet having through
holes with the same pattern as the contact sheets, and each of the
two contact sheets has the same number of contact springs on both
sides of the adhesive sheet.
13. A contact sheet according to claim 11, wherein said contact
sheet is an anisotropic conductive film.
14. A contact sheet according to claim 12, wherein said contact
sheet is an anisotropic conductive film.
15. A contact sheet according to claim 11, wherein said cantilevers
of said contact springs arranged on both sides of the adhesive
sheet are in contact with each other with applying pressure to each
other before an integrated circuit.
16. A contact sheet according to claim 12, wherein said cantilevers
of said contact springs arranged on both sides of the adhesive
sheet are in contact with each other with applying pressure to each
other before an integrated circuit.
17. A contact sheet according to claim 1, wherein two sheets
composed of an insulative elastic material are superposed and one
end of said cantilever is bonded to said two sheets so as to fix
said cantilever to said sheet, resultantly without space for
detaching a connecting bar.
18. A contact sheet according to claim 3, wherein two sheets
composed of an insulative elastic material are superposed and one
end of said cantilever is bonded to said two sheets so as to fix
said cantilever to said sheet, resultantly without space for
detaching a connecting bar.
Description
CROSS REFERENCE OF THE RELATED APPLICATION
[0001] The present application is a continuation-in-part
application of U.S. patent application No. 09-410,377 filed on Sep.
30, 1999.
BACKGROUND OF THE INVENTION AND THE RELATED ART
[0002] The present invention relates to a contact sheet used with a
socket employed for connecting an integrated circuit having
spherical terminals arranged in a grid pattern, and a board, and
used especially with a thin socket employed for high-frequency
testing or mounting.
[0003] In recent years, because of the demands for reduced sizes
and higher speed in information processing equipment, the pitches
in integrated circuits are increasingly becoming smaller, and the
mounting method is shifting from through-hole to surface mounting,
and the arrays of terminals are shifting from peripheral arrays to
grid arrays. As a result, ball grid array (BGA) devices are
becoming the mainstream of packages as they permit surface mounting
even for grid arrays.
[0004] A socket is used between a BGA type integrated circuit
device and a board when conducting a burn-in test or a
high-frequency test of the integrated circuit, and the socket is
also mounted on a board when replacing an integrated circuit. In a
socket, all contacts must be in secure contact with both terminals
of an integrated circuit and terminals of a board in order to
ensure sufficient electrical conduction.
[0005] On the other hand, in recent years, with the increasing
speed of MPUs or memories, the demand for lower inductance with
respect to faster clocks has been arising. To meet the demand, it
is necessary to minimize the distance over which currents pass in a
contact placed between a terminal of an integrated circuit and a
terminal of a board.
[0006] As a thin connector or socket with a small pitch, a
component called "an anisotropic conductive sheet" has
conventionally been used. There have been known, for example, a
conductive sheet in which conductive elastomers or metal wires are
arranged in an insulative elastomer (U.S. Pat. No. 3,862,790 and
U.S. Pat. No. 4,295,700) and one in which conductive particles are
added (Japanese Unexamined Patent Publication No. 6-82521). FIG. 12
shows a conventional example wherein thin metal wires 31 are
embedded in a silicone rubber 30 at a high density.
[0007] Furthermore, as conductive sheets to which considerations
have been given to the aspects of BGAs that their spherical
terminals are soft and their surfaces are made of solder coated
with oxide films, there are one with dendrites grown on contact
portions (U.S. Pat. No. 5,691,041), one in which cantilevers having
protrusions are fixed on a flexible board (U.S. Pat. No.
5,629,837), one in which the surfaces of terminals on a flexible
board have been provided with asperities by chemical processing or
the like (Japanese Unexamined Patent Publication No. 10-32070), and
one in which innumerable protrusions are formed by thermal spraying
or the like (Japanese Unexamined Patent Publication No. 10-144440),
etc.
[0008] Furthermore, as ones with a structure for avoiding contact
with ball tips while destroying oxide films on solder surfaces,
there are one having Y-shaped contacts (Japanese Unexamined Patent
Publication No. 9-21847), and one inserted in finger springs (U.S.
Pat. No. 5,702,255 and U.S. Pat. No. 5,730,606).
[0009] As the number of terminals of an integrated circuit
increases, a force required for insertion increases. There is a
contact sheet having a structure in which the foregoing force is
reduced to zero, and spherical terminals are pushed laterally later
by using a lever or the like (U.S. Pat. No. 5,578,870 and U.S. Pat.
No. 5,637,008). As this type, one employing vertically long
cantilevers is the mainstream. Moreover, there is a socket
described in Japanese Unexamined Patent Publication No. 9-55273
that permits replacement of contact portions while solving the
problem peculiar to solder balls mentioned above.
[0010] However, in an anisotropic conductive sheet employing the
elastomer as shown in FIG. 12, mostly, terminals having flat
surfaces provided with gold plating are connected. If this
conductive sheet is used for connection with a BGA having spherical
terminals made of solder, solder surfaces will inevitably be
dented, posing a problem of unstable electrical contact.
[0011] Furthermore, in those with asperities or protrusions formed
on the surfaces of the terminals on the flexible boards, variations
in height of terminals will cause insufficient electrical
conduction in some circuits. In the Y-shaped contacts, the distance
over which currents pass is relatively long, making them unsuited
as contacts for high-frequency testing or mounting although
reliable electrical conduction can be ensured.
[0012] The present invention has been made with a view toward
solving the problems, and an object thereof is to provide a contact
sheet that enables reliable electrical contact to be obtained by
removal of an oxide film from a solder surface, is capable of
accommodating variations in height or size of spherical terminals,
prevents collapse of a tip, features a short distance over which
currents pass, permits a zero insertion force (ZIF) structure to be
implemented as necessary, and also enables a structure for
permitting replacement to be implemented.
SUMMARY OF THE INVENTION
[0013] More specifically, according to the present invention, there
is provided a contact sheet used for a socket to connect an
integrated circuit having spherical terminals and a board, having
protruding contact springs in some or all of numerous through holes
provided in a sheet composed of an insulative elastic material,
wherein the contact springs are composed of a conductive material
and constituted by two or more cantilevers fixed onto the sheet by
bonding or clamping one end thereof, each cantilever has a lower
supporting portion and a spherical terminal holding portion, the
lower supporting portion is composed of a linear portion or a
planar portion formed adjacently to a portion fixed to the sheet,
the spherical terminal holding portion is formed by vertically
bending the other end of the cantilever toward one of two openings
of a through hole, the spherical terminal enters into a gap at the
spherical terminal holding portion of the two or more cantilevers
when the integrated circuit is mounted, and thereby the spherical
terminal holding portions of the two or more cantilevers are pushed
and spread in a direction away from the portion of each cantilever
that is fixed to the sheet, and at the same time, a boundary
portion between the spherical terminal holding portions and the
lower supporting portion is pressed against the board.
[0014] Preferably, in the contact sheet set forth above, each
contact spring is composed of three cantilevers, the three
cantilevers are disposed virtually parallel to each other in the
through hole, and two cantilevers on both ends of the three
cantilevers and the middle cantilever are fixed to edges of the
through hole that oppose each other because contact pressure on
spherical terminals is well-balanced between a direction along the
line and the direction perpendicular to the line, which makes
spotting possible.
[0015] Furthermore, according to the present invention, there is
provided a contact sheet used for a socket for achieving connection
between an integrated circuit having spherical terminals and a
board, having protruding contact springs in some or all of numerous
through holes provided in a sheet composed of an insulative elastic
material, wherein each of the contact springs is constituted by two
or more cantilevers composed of a conductive material, the two or
more cantilevers are respectively fixed to adjoining edges of the
through hole at one end thereof so that each of them has two end
portions and they are oriented in parallel to each other, each
cantilever has a lower supporting portion and a spherical terminal
holding portion, the lower supporting portion is composed of a
linear portion or a planar portion formed adjacently to a portion
fixed to the sheet, the spherical terminal holding portions are
formed by vertically or obliquely bending the other ends of the two
or more cantilevers toward one of two openings of a through hole,
and when the integrated circuit is mounted, the spherical terminals
push and spread the spherical terminal holding portions of the two
or more cantilevers in a direction away from the portion of each
cantilever that is fixed to the sheet and a boundary portion
between the spherical terminal holding portions and the lower
supporting portion is pressed against the board.
[0016] It is preferable that dispositions of two or more
cantilevers installed in a through hole of an arbitrary one column
and dispositions of the two cantilevers installed in a through hole
of another column adjacent to the one column have a point
symmetrical relationship because contact pressure on spherical
terminals in a direction of a line is well-balanced by a pair of
holes with the adjacent line, which makes spotting possible.
[0017] It is preferable in a contact sheet of the present invention
that a through hole has a shape of a rectangle and a longitudinal
direction of the rectangle coincides with a diagonal direction with
reference to the disposition of the spherical terminals because the
cantilevers can be made long, much displacement can be taken, and
permanent set in fatigue as a spring is small.
[0018] Preferably, in the contact sheet in accordance with the
present invention, it is preferable that each contact spring is
composed of two or more cantilevers, the two or more cantilevers
are disposed parallel to one another in the through hole, and a
bridge connecting the lower supporting portion of the two or more
cantilevers fixed to edges of the through holes adjacent to each
other among the two or more cantilevers is provided because it
avoids more than necessary separation of two spherical terminal
holding portions when spherical terminals enters into the spherical
terminal holding portions.
[0019] Further, as shown in FIG. 3(a), a cantilever of a contact
sheet is preferably in contact with the board before an integrated
circuit is mounted because the securer electrical conduction can be
ensured.
[0020] In the present invention, it is preferable that two contact
sheets are unitarily formed by means of an adhesive sheet having
through holes of the same pattern as the contact sheets, and each
of the contact sheets has the same number of contact springs on
both sides of the adhesive sheet.
[0021] In addition, cantilevers of the contact springs provided on
both side of the adhesive sheet are mutually in contact with one
another with mutually applying pressure before the integrated
circuit is mounted. For such an adhesive sheet, an anisotropic
conductive membrane may be used.
[0022] Furthermore, in the contact sheet in accordance with the
present invention, it is preferable that two sheets composed of an
insulative elastic material are superposed and that one end of the
cantilever is bonded by the two sheets so as to fix the cantilever
to the sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective view showing an example of a first
contact sheet in accordance with the present invention.
[0024] FIG. 2 (a) and (b) are schematic representations showing a
mode for mounting an integrated circuit on the first contact sheet
in accordance with the present invention, wherein FIG. 2 (a) shows
a state before mounting, and FIG. 2 (b) shows a state after
mounting.
[0025] FIG. 3 (a) and (b) are schematic representations showing
another mode for mounting an integrated circuit on the first
contact sheet in accordance with the present invention, wherein
FIG. 3 (a) shows a state before mounting, and FIG. 3 (b) shows a
state after mounting.
[0026] FIG. 4 is a perspective view showing an example of a second
contact sheet in accordance with the present invention.
[0027] FIG. 5 is a perspective view showing another example of the
second contact sheet in accordance with the present invention.
[0028] FIG. 6 (a) and (b) are schematic representations showing a
mode for mounting an integrated circuit on the second contact sheet
in accordance with the present invention, wherein FIG. 6 (a) shows
a state before mounting, and FIG. 6 (b) shows a state after
mounting.
[0029] FIG. 7 (a) - (c) are schematic sectional views showing an
embodiment of a cantilever in the first and second contact sheets
in accordance with the present invention, wherein FIG. 7 (a) shows
one example, FIG. 7 (b) shows another example, and FIG. 7 (c) shows
still another example.
[0030] FIG. 8 is a schematic representation illustrating balance of
a force in the first and second contact sheets in accordance with
the present invention.
[0031] FIG. 9 is a schematic representation illustrating a contact
point of a contact spring and a spherical terminal in a contact
sheet in accordance with the present invention.
[0032] FIG. 10 is a perspective view showing an example of a
contact sheet for application to a socket of a ZIF structure.
[0033] FIG. 11 (a) and (b) are schematic representations showing a
mode wherein a contact sheet in accordance with the present
invention is applied to the ZIF structure and an integrated circuit
is mounted thereon, wherein FIG. 11 (a) shows a state before
operation and FIG. 11 (b) shows a state after operation.
[0034] FIG. 12 is a schematic sectional view showing an example of
a conventional contact sheet.
[0035] FIG. 13 is a perspective view showing an example having a
bridge of the first and the second contact sheets of the present
invention.
[0036] FIG. 14 (a) (d) are explanatory views showing a mode wherein
an integrated circuit is mounted on a contact sheet in accordance
with the present invention, wherein FIG. 14 (a) shows a state
before mounting, FIG. 14 (b) shows a state after mounting, FIG.
14(c) is a deal drawing of a contact sheet, and FIG. 14(d) is a
deal drawing of a contact sheet using an anisotropic conductive
membrane for an adhesive sheet.
[0037] FIG. 15 (a) - (e) are explanatory views showing various
modes wherein an integrated circuit is mounted on a contact sheet
in accordance with the present invention. FIG. 15 (a) - (b) show
examples wherein an integrated circuit having spherical terminals
thereon is mounted and a contact spring is composed of two
cantilevers, wherein FIG. 15 (a) shows the case of one contact
sheet, and FIG. 15 (b) shows the case of two contact sheets. FIG.
15 (c) - (e) show examples wherein an integrated circuit having a
plane terminal thereon. FIG. 15(c) shows the case of one contact
sheet wherein a contact spring is composed of two cantilevers, FIG.
15(d) shows the case of one contact sheet wherein a contact spring
is composed of three cantilevers, and FIG. 15(e) shows the case of
two contact sheets wherein a contact spring is composed of three
cantilevers.
[0038] FIG. 16 (a) and (b) are schematic representations showing a
mode wherein an integrated circuit having an LGA is mounted on a
contact sheet in accordance with the present invention, wherein
FIG. 16 (a) shows a state before mounting, and FIG. 16 (b) shows a
state after mounting.
[0039] FIG. 17 (a) and (b) are schematic representations showing a
mode wherein an integrated circuit having an LGA is mounted on a
contact sheet in accordance with the present invention, wherein
FIG. 17 (a) shows a state before mounting, and FIG. 17 (b) shows a
state after mounting.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] As shown in FIG. 1, a first contact sheet 5 in accordance
with the present invention has protruding contact springs 3 in some
or all of numerous through holes 2 provided in a sheet 1 formed of
an insulative elastic material. The contact springs 3 are formed of
a conductive material having two end portions and constituted by
two or more facing cantilevers 9 (9a, 9b, and 9c) that are fixed to
the sheet 1 by bonding at one end thereof. Each of the cantilevers
9a, 9b, and 9c has a lower supporting portion 10 and a spherical
terminal holding portion 11, the lower supporting portion 10 is
composed of a planar portion formed adjacently to a portion fixed
to the sheet 1, and the spherical terminal holding portion 11 is
formed by vertically bending the other end of the cantilever 9
toward one of two openings of the through hole 2.
[0041] When mounting an integrated circuit 7, a spherical terminal
6 of the integrated circuit 7 such as a BGA package enters in a gap
between the spherical terminal holding portions 11 of two or more
cantilevers 9 (9a, 9b, and 9c), causing the lower supporting
portions 10 of the cantilevers 9 to flex toward the other openings,
and after the lower supporting portions 10 come in contact with a
board 8, the spherical terminal holding portions 11 of the two or
more cantilevers 9 are pushed and spread in a direction away from
the portions of the individual cantilevers 9 that are fixed to the
sheet 1 as illustrated in FIG. 2 (a) and FIG. 2 (b). Reference
numeral 4 denotes a spacer.
[0042] When the cantilever 9 of the contact spring 3 has a shape as
shown in FIG. 3 (a), the moment the spherical terminal 6 of the
integrated circuit 7 such as a BGA package enters the gap of the
spherical terminal holding portions 11 of the cantilevers 9, the
contact sheet 5 is pressed against the board 8, causing the
spherical terminal holding portions 11 to be narrower, and entry of
the spherical terminal 6 into the narrowed spherical terminal
holding portions 11 causes the spherical terminal holding portions
11 to be pushed and spread in a direction away from the portions of
the individual cantilevers 9 that are fixed to the sheet 1 as shown
in FIG. 3 (b). In this case, the lower supporting portions 10 is
bent toward the board 8 side, and a boundary portion between the
spherical terminal holding portions 11 and the lower supporting
portion 10 is in contact with the board 8 in advance even if the
integrated circuit 7 is not mounted. Therefore, securer electric
conductivity can be obtained, and reliability is enhanced.
[0043] In the contact sheet 5 mentioned above, the respective
cantilevers 9 are long since they have the lower supporting
portions 10 and the spherical terminal holding portions 11, and
they, as springs, do not incur permanent set in fatigue since much
displacement can be secured when the spherical terminals are
pressed against them. Moreover, since the spherical terminal
holding portions 11 are vertically bent, they hardly spread
laterally when subjected to vertical displacement of the spherical
terminals. Therefore, variations in height of spherical terminals
of integrated circuits or warps in integrated circuits or boards,
if any, can be absorbed by the spring without permanent set in
fatigue to ensure electrical conduction between an integrated
circuit and a board.
[0044] Furthermore, the spherical terminal holding portions 11 of
the cantilevers 9 are formed by vertically bending one end of each
of the cantilevers 9 toward one of two openings of each of the
through hole 2, and the spherical terminal 6 pushes and spreads the
respective cantilevers 9 to enter gaps of the spherical terminal
holding portions 11 of the respective cantilevers 9; hence, the
spherical terminal 6 comes in contact with the cantilever 9 at a
side surface thereof and a distal end portion of the spherical
terminal 6 does not come in contact with the lower supporting
portion 10, eliminating chances of crushing the distal end portion
of the spherical terminal 6. Moreover, at the time of mounting an
integrated circuit on a board, when the spherical terminal 6 enters
in a gap of the spherical terminal holding portions 11 while
pushing and spreading the spherical terminal holding portions 11 of
the cantilevers 9, an oxide film is scraped off by edges of end
portions of the cantilevers 9, thus securing reliable electrical
conduction. In addition, conduction between a terminal of the board
8 and the cantilevers 9 is accomplished when the spherical terminal
6 pushes and causes the lower supporting portions 10 of the
cantilevers 9 to flex, causing a portion of the cantilevers 9 to
come in contact with the terminal of the board. Hence, the distance
over which currents pass in the contact springs 3 can be shortened
and an inductance in relation to fast clocks can be reduced, making
the contact sheet ideally used for mounting and high-frequency
testing. Specifically, in the contact sheet described above, the
current passing distance in the contact springs can be reduced to
about a radius of the spherical terminal, or 0.15 to 0.5 mm to be
more specific.
[0045] In the contact sheet 5 set forth above, the respective
cantilevers 9 are disposed such that they underlie the spherical
terminal 6, allowing the lower supporting portions 10 of the
respective arms 9 to be made longer. Accordingly, when mounting an
integrated circuit on the board via the contact sheet 5, a large
displacement can be allowed within the elasticity of the contact
springs, so that unnecessary load will not be applied to the board.
In addition, the contact springs will not break easily.
[0046] In the contact sheet described above, each of the contact
springs 3 may be composed of three cantilevers 9 (9a, 9b, and 9c),
the three cantilevers 9 may disposed virtually parallel to each
other in the through holes 2, and two cantilevers 9a and 9b on both
ends of the three cantilevers 9 and the middle cantilever 9c may be
fixed to edges of the through holes 2 that oppose each other as
shown in FIG. 1. This arrangement permits easier positioning of an
integrated circuit having the spherical terminals 6 also by the
contact sheet 5.
[0047] Furthermore, the contact sheet set forth above may be
configured as shown in FIG. 4, wherein each contact spring 3 is
formed of two cantilevers 9 (9d and 9e), the two cantilevers 9 are
disposed parallel to each other in the through holes 2, the two
cantilevers 9 are fixed to edges of the through holes 2 that oppose
each other, and a disposition of the two cantilevers 9d and 9e
installed in a through hole 2a of an arbitrary one column and a
disposition of another two cantilevers 9f and 9g installed in a
through hole 2b of another column adjacent to the foregoing one
column are in a mirror image relationship. The mirror image
relationship of the dispositions of the cantilevers in adjoining
columns permits easier positioning of an integrated circuit having
spherical terminals in relation to the contact sheet 5. More
specifically, if the contact sheet 5 is formed of two cantilevers
9, there is no force to restrict the spherical terminal in a
direction indicated by an arrow in FIG. 4, and therefore,
positioning is impossible even if the spherical terminal is placed
in the gap at the spherical terminal holding portions of the two
cantilevers. However, the spherical terminals escape in different
directions in the adjacent columns cancel each other as shown in
FIG. 4 when the cantilevers 9 of adjacent columns are disposed to
carry the mirror image relationship, thus making positioning
easier.
[0048] A second contact sheet in accordance with the present
invention has protruding contact springs 3 in some or all of
numerous through holes 2 provided in a sheet 1 formed of an
insulative elastic material, and the contact springs 3 are
constituted by two or more cantilevers 9 formed of a conductive
material as shown in FIG. 5. The two or more cantilevers 9 are
individually fixed at one end thereof on adjoining edges of the
through holes 2 such that they have two end portions and are
parallel to each other, each of the cantilevers 9 having a lower
supporting portion 10 and a spherical terminal holding portion 11.
The lower supporting portion 10 is composed of a linear portion or
a planar portion formed adjacently to a portion fixed to the sheet
1, the spherical terminal holding portion 11 is formed by bending
the other end of the two or more cantilevers 9 toward one of two
openings of a through hole.
[0049] When an integrated circuit 7 is mounted, a spherical
terminal 6 pushes and spreads the spherical terminal holding
portions 11 of the two or more cantilevers 9 in a direction away
from portions of the respective cantilevers 9 that are fixed to the
sheet 1 and also flexes the lower supporting portions 10 toward a
surface away from the sheet 1 as illustrated in FIG. 6 (a) and FIG.
6 (b).
[0050] It is preferable that dispositions of two or more
cantilevers 9h and 9i installed in a through hole 2a of an
arbitrary one column and dispositions of two cantilevers 9j and 9k
installed in a through hole 2b of another column adjacent to the
foregoing one column have a point symmetrical relationship because
contact pressure on the spherical terminal in a direction of a line
is well-balanced by a pair of holes with the adjacent lines to fix
a position of a ball by the contact.
[0051] Due to the same reason as that in the first contact sheet in
accordance with the present invention, the contact sheet described
above protects a distal end portion of a spherical terminal,
ensures secure electrical conduction by removing an oxide film, and
shortens a current passing distance in a contact spring, allowing
inductance in relation to fast clocks to be reduced. In this case,
it is preferable to dispose the cantilevers 9 so that they are
oriented parallel to a direction of a column to which the through
hole 2 where the cantilevers are installed belongs as shown in FIG.
5.
[0052] In the first and second contact sheets in accordance with
the present invention, the cantilevers are bent to form the
spherical terminal holding portions. There are no particular
restrictions on how the cantilevers are bent as long as a spherical
terminal can be set in a gap at the spherical terminal holding
portions by pushing and spreading the spherical terminal holding
portions, the spherical terminal holding portions are able to hold
a spherical terminal at a portion other than a distal end portion
of the spherical terminal, and an oxide film can be scraped off by
edges of the cantilevers when the spherical terminal pushes and
spreads the spherical terminal holding portions. For instance, the
cantilever may be bent at one point as illustrated in FIG. 7 (a),
it may be bent at two points as illustrated in FIG. 7 (b), or it
may be continuously bent into an arc shape as illustrated in FIG. 7
(c). Furthermore, the cantilevers 9 may be formed by a long and
slender plate-like member or by a linear member.
[0053] In the first and second contact sheets in accordance with
the present invention, in a state where an integrated circuit
having spherical terminals has been mounted, it is desirable that a
force of the spherical terminal 6 pushing the spherical terminal
holding portions 11 of the cantilever 9 is greater than a force of
the spherical terminal 6 pushing the contact springs 3 in a
perpendicular direction in relation to the sheet 1 as shown in FIG.
8. This effectively scrapes an oxide film of the spherical terminal
and minimizes a force required for mounting or removing an
integrated circuit thereby to prevent an extra force from being
applied to a board. More specifically, when mounting an integrated
circuit having numerous terminals as an integrated circuit having a
grid arrangement on a board, a force applied to the board is a
total sum of forces applied by respective terminals of the
integrated circuit. Hence, in order to prevent damage to the board,
it is necessary to minimize forces of spherical terminals pushing
contact springs against a sheet in a vertical direction.
Preferably, surfaces of the spherical terminals are scraped by 0.01
to 0.05 mm to effectively remove an oxide film.
[0054] In addition, in the first and second contact sheets in
accordance with the present invention, it is preferable that each
contact spring is composed of two or more cantilevers, the two or
more cantilevers are disposed in parallel with each other in a
through hole, and there is provided a bridge 13 for mutually
connecting the lower supporting portion 10 of two or more
cantilevers 9 fixed to mutually adjacent edges of the through hole
2 as shown in FIG. 13 in the case that two or more cantilevers
fixed to mutually adjacent edges of the through hole among the two
or more cantilevers. The bridge 13 can prevent the spherical
terminal holding portions 11 from being extended right and left,
i.e., in a direction perpendicular to the opening portion of the
through hole 2 more than necessary when a spherical terminal 6 gets
into the spherical terminal holding portions 11. Incidentally, if
the bridge is too far from the spherical terminal 6, the spherical
terminal holding portion 11 is widely extended. If the bridge 13 is
present in a portion in contact with the board 8 and the planar
terminal 16, the two or more cantilevers 9 hardly move
independently, and it sometimes happens that the number of contact
points between the spherical terminal holding portion 11 and the
spherical terminal 6, the board 8, the planar terminal 16 or the
like are decreased. Therefore, it is preferable that the bridge 13
is placed in a position as near to the planar terminal 6 as
possible without a portion in contact with the board 8 or the
planar terminal 16.
[0055] In the first and second contact sheets in accordance with
the present invention, it is also preferable that two contact
sheets are unitarily formed by means of an adhesive sheet having
through holes in the same pattern as the contact sheets and that
each of the two contact sheets is a two-ply contact sheet having
the same number of contact springs on both sides of the adhesive
sheet. By using the two-ply contact sheet, the displacement can be
twice as large as a contact sheet even if contact springs having
the same elasticity are used. FIGS. 14 (a) - (d) show an embodiment
of a two-ply contact sheet. FIG. 14(a) shows a state before an
integrated circuit 7 is mounted, FIG. 14(b) shows a state after the
integrated circuit 7 is mounted.
[0056] Contact springs may be plane-symmetric with the adhesive
sheet being centered or may have different shapes irrelevant to one
another. In a two-ply contact sheet shown in FIGS. 14(a) - (d), the
contact springs 3 are not plane-symmetric with the adhesive sheet
12 being centered but of different shapes irrelevant to one
another. However, in a contact spring 3 on the side of the board 8,
a tip of a portion corresponding to a spherical terminal holding
portion is rounded so as not to damage the planar terminal on the
side of the board 8.
[0057] In addition, if cantilevers of two contact springs on both
side of the adhesive sheet are bent in a direction where they are
brought into contact with each other before they are bonded, they
contacts each other with applying pressure to each other before an
integrated circuit is mounted, and securer electric conductivity is
ensured to increase reliability.
[0058] For an adhesive sheet, an anisotropic conductive membrane as
shown in FIG. 14(d) can be suitably used. An anisotropic conductive
membrane is a sheet showing conductivity in a direction of
thickness and insulating ability in a transverse direction and
using an adhesive agent as a substrate. The membrane can bond a
metal and an insulator at the same time, and besides it prevent
electric current from leakage due to the characteristic, secure
electric conductivity can be ensured to further improve
reliability.
[0059] In the first and second contact sheets in accordance with
the present invention, it is preferable that a magnitude of an
angle formed by a straight line connecting a contact point of the
cantilever 9 and a spherical terminal 6 and a central point of a
spherical terminal 6 and a perpendicular drawn from the central
point of the spherical terminal 6 to the sheet 1 ranges from 30 to
70 degrees as illustrated in FIG. 9 in a process for mounting an
integrated circuit having spherical terminals and in a state
wherein the integrated circuit has been mounted. If the angle is
below 30 degrees, then distal end portions of the spherical
terminals may be scratched, while if the angle exceeds 70 degrees,
then it is difficult to effectively hold the spherical terminals.
From a viewpoint of appropriately reducing the force of the
spherical terminals pushing the contact springs against the sheet
in the vertically direction, it is further preferable to set the
magnitude of the angle, which is formed by the straight line
connecting the contact point of the cantilever and the spherical
terminal with a central point of the spherical terminal and a
perpendicular drawn from the central point of the spherical
terminal to the sheet, to 45 to 60 degrees. The angle mentioned
above can be adjusted by appropriately adjusting a diameter of the
spherical terminal, a thickness of a sheet constituting the contact
sheet, and an angle at which the cantilever is bent.
[0060] The contact sheet in accordance with the present invention
is also suitably used with a socket having a zero insertion force
(ZIF) structure. For example, a contact sheet shown in FIG. 10 has
protruding contact springs 3 in some or all of numerous through
holes 2 provided in a sheet 1 formed of an insulative elastic
material, and each of the contact springs 3 is formed of two or
more cantilevers 9 made of a conductive material having two
terminals as in the case of the contact sheet of FIG. 5. The two or
more cantilevers 9 are respectively bonded to adjacent edges of a
through hole 2 at one end thereof such that they are oriented in
parallel to each other, and each cantilever 9 has a lower
supporting portion 10 and a spherical terminal holding portion 11.
The lower supporting portions 10 are composed of planar portions
formed adjacently to portions fixed to the sheet 1, and the
spherical terminal holding portions 11 are formed by bending the
other ends of the two or more cantilevers 9 toward one of two
openings of the through hole 2.
[0061] FIG. 11 (a) and FIG. 11 (b) illustrate examples wherein
sockets of the ZIF structure have been configured using the
contacts sheets shown in FIG. 10 described above.
[0062] As shown in FIG. 11 (a) and FIG. 11 (b), in the ZIF
structure, after the integrated circuit 7 has been mounted, it does
not vertically shift; only a spacer 4 slides in the direction of an
arrow (a lateral direction) of FIG. 11 (b) to mount the integrated
circuit 7. In this case, a side surface portion of the spacer 4
that comes in contact with the spherical terminal 6 is formed to
have a slope surface so that it comes in contact with and pushes an
upper portion of the spherical terminal 6. Hence, the spherical
terminal 6 pushes and spreads the spherical terminal holding
portions 11 of the two or more cantilevers 9 in a direction away
from the portions of the respective cantilevers 9 that are fixed to
the sheet 1, and also flexes the lower supporting portions 10
toward a surface away from the sheet 1.
[0063] In the socket having such a ZIF structure, using a sheet of
10 to 40 .mu.m as the contact sheet reduces a pressure of contact
with the spherical terminal 6, so that a contact resistance of the
whole can be reduced by increasing the number of contacts.
[0064] In the contact sheets in accordance with the present
invention, the openings of the through holes may have a
rectangular, triangular, round, or elliptic shape, etc.; however,
the shape is preferably rectangular. In addition, when the openings
are round, the diameter preferably ranges from 0.3 to 1.5 mm. If
the diameter is below 0.3 mm, then manufacture will be difficult;
if the diameter exceeds 1.5 mm, then no small pitch can be
accomplished, meaning that means other than the present invention
can be used.
[0065] Further preferably, the pitch of the through holes ranges
from 0.25 to 1.5 mm. If the pitch is below 0.25 mm, then sufficient
assembly accuracy cannot be secured; if the pitch exceeds 1.5 mm,
then no advantages of an integrated circuit will be provided.
[0066] A conductive material employed for the contact sheets in
accordance with the present invention is required to have strength,
wear resistance, flexibility, oxidization resistance, etc. in
addition to conductivity. It is especially desirable to use a
spring material such as beryllium copper or nickel beryllium. Using
these materials as the conductive material makes it possible to
impart fatigue property and heat resistance to high temperatures to
the contact sheets in accordance with the present invention.
[0067] Preferably, the thickness or size of the cantilever as the
contact spring ranges from 0.01 to 0.1 mm, and more preferably, it
ranges from 0.02 to 0.05 mm. This is because of the following
reason: if the thickness or size is below 0.01 mm, then the
strength of the cantilever will be too small, making it difficult
to obtain an appropriate contact load; if it exceeds 0.1 mm, then
the elasticity range of the materials will be exceeded, so that
terminals of an integrated circuit will not be able to take a
sufficient displacement to press the cantilever against an element
to be connected that exists on an opposite side of a sheet, making
it difficult to secure a stable continuity.
[0068] An elastic material constituting the contact sheets is
required to exhibit resistance to heat, weather, etc., and a rubber
such as a silicone rubber or a synthetic rubber, or a resin such as
a polymer, a polyimide, or an engineering resin is used. A
polyimide constituent in particular is suitably used.
[0069] Moreover, the contact sheets in accordance with the present
invention can be ideally used as contact boards when mounting
integrated circuits having spherical terminals on boards. To be
more specific, the contact sheets can be ideally used when mounting
integrated circuits provided with spherical terminals on a mounting
board, testing board, etc. In particular, the contact sheets in
accordance with the present invention can be suitably used for
integrated circuits having grid arrays having terminal pitches
ranging from 0.5 to 1.5 mm, the number of terminals thereof ranging
from 500 to 2000. Reliable electrical conduction can be secured in
integrated circuits having multi-pin grid arrays that have
conventionally been prone to incur unstable electrical conduction
if warps occur.
[0070] The terminals of integrated circuits may be spherical or
planar (LGA: land grid array). FIG. 16 (a) and FIG. 16 (b) show
examples wherein an LGA integrated circuit 15 is mounted on a board
8. A planar terminal 16 pushes from above terminal holding portions
14 with a rounded tip of two or more cantilevers 9, causing the
spherical terminal holding portions 14 of the cantilevers 9 to be
pushed and spread in a direction away from portions of the
respective cantilevers 9 that are fixed to a sheet 1 and, at the
same time, pressed against the board, thus securing contact.
[0071] Also in an integrated circuit having LGA, the lower
supporting portion 10 is bent on the side of the board 8 as shown
in FIG. 16(a) and FIG. 16(b). Even if the integrated circuit 7 is
not mounted, contact resistance is lowered to increase reliability
by a contact sheet whose lower supporting portion 10 is previously
in contact with the substrate 8.
[0072] Also in a planar terminal, two-ply contact sheet can make
displacement twice as large as a contact sheet having contact
springs having the same elasticity.
[0073] In a two-ply contact sheet, it is preferable that
cantilevers of two contact spring on both sides of the adhesive
sheet are brought into contact with each other with applying
pressure to each other before the integrated circuit is mounted
because reliability is increased. FIG. 17 shows an embodiment of a
cantilever in a two-ply contact sheet of the present invention in
the case that it is used in an integrated circuit having LGA.
[0074] FIGS. 15(a) - (e) show various embodiments in which an
integrated circuit is mounted on a contact sheet of the present
invention.
[0075] FIGS. 15(a) - (b) are embodiments where an integrated
circuit having a spherical terminal is mounted and where a contact
spring is constituted by two cantilevers. FIG. 15(a) shows a case
of a contact sheet, and FIG. 15(b) shows a case of two contact
sheets. In the case of two contact sheets of FIG. 15(b),
displacement can be twice as large as a case of one contact sheet
of FIG. 15(a).
[0076] FIGS. 15(c) - (e) is an embodiment where an integrated
circuit having a planar terminal is mounted. FIG. 15(c) shows the
case of one contact sheet where a contact spring is constituted by
two cantilevers, FIG. 15(d) shows the case of one contact sheet
where a contact spring is constituted by three cantilevers, and
FIG. 15(e) shows the case of two contact sheets where a contact
spring is constituted by three cantilevers. If the same cantilevers
are used, contact load is in proportion to the number of
cantilevers. That is, it is possible for the contact sheet having
three cantilevers of FIGS. 15(d) and 15(e) to be subjected to
contact load by 1.5 times larger than a contact sheet having two
cantilevers of FIG. 15(a) and 15(b).
[0077] The contact sheet in accordance with the present invention
is manufactured according to, for example, a method described
below.
[0078] First, a sheet formed of a conductive material is bonded to
a sheet having numerous through holes and composed of an insulative
elastic material, then etching or the like is performed thereon
such that only portions where contact springs will be formed are
left unetched, and the portions where the contact springs will be
formed are cut and bent by press work or the like. As necessary,
before or after the pressing work, the contact springs may be
provided with plating. Lastly, another sheet composed of an elastic
material is bonded on a side where the contact springs are exposed
to complete the contact sheet in accordance with the present
invention. It is a matter of course that this process may be
conducted before press machining.
[0079] Alternatively, first, sheets where in the contact springs
are joined are produced by subjecting a sheet formed of a
conductive material to etching, pressing, etc., then the sheets are
sandwiched and bonded between two sheets having through holes and
formed of insulative elastic material, and the contact springs are
cut by pressing or the like, and the laminate is subjected to
bending. The cutting and bending work by pressing or the like may
be performed with the portions, where the contact springs will be
formed, bonded to one of the sheets formed of an elastic material.
Furthermore, the contact springs may be provided with plating
before or after the pressing work.
[0080] A two-ply contact sheet which can have twice as much
displacement is produced by preparing two contact sheet produced by
any one of the aforementioned methods, preparing an adhesive sheet
having the same pattern of through holes, putting the adhesive
sheet between the two contact sheet so that the pattern of
throughholes of the adhesive sheet matches those of the two contact
sheets, and subjecting them to thermocompression bonding.
Embodiments
[0081] The present invention will be described in more detail in
conjunction with embodiments; however, the present invention is not
limited to the embodiments.
First Embodiment
[0082] A total of 529 through holes, 23 columns.times.23 rows, at
1.0-mm pitches were provided in a polyimide sheet (brand name:
YUPIREX, produced by Ube Kosan Co., Ltd.) which is 1.0 .mu.m thick
and provided with a 10 .mu.m-thick adhesive layer on one surface
thereof. Each of the through holes is rectangular, measuring 0.5 mm
long and 1.0 mm wide. The through holes 2 were arranged such that
the respective sides of the through holes 2 and the respective
columns formed by the through holes 2 are oriented at an angle of
45 degrees with respect to the respective sides of the polyimide
sheet 1.
[0083] Next, a beryllium copper plate which is 30 .mu.m thick was
attached by thermocompression bonding onto a surface of a polyimide
sheet that is provided with an adhesive layer, and etching was
carried out, leaving contact springs.
[0084] Subsequently, another polyimide sheet provided with through
holes and the polyimide sheet with the foregoing beryllium copper
sections left unetched were bonded to each other by
thermocompression bonding. At this time, the sheets were bonded
such that the surface having the adhesive layer faced the beryllium
copper sections.
[0085] Subsequently, the sections remaining in the rectangular
through holes were cut by pressing and bent in the middle thereof
to be formed into cantilevers having a predetermined shape. As
necessary, heat treatment such as age hardening treatment may be
performed at this stage. Thereafter, nickel/gold plating was
conducted to produce the contact sheet in accordance with the
present invention shown in FIG. 1.
[0086] When an integrated circuit having spherical terminals was
mounted on a mounting board via the foregoing contact sheet, an
oxide film was effectively removed and stable electrical conduction
was obtained. Moreover, no crushed distal end portions of the
spherical terminals were observed.
Second Embodiment
[0087] A total of 529 through holes, 23 columns.times.23 rows, at
1.0-mm pitches were provided in each of two polyimide sheets (brand
name: YUPIREX, produced by Ube Kosan Co., Ltd.) which are 50 .mu.m
thick and provided with a 10 .mu.m-thick adhesive layer on one
surface each. Each of the through holes was rectangular, measuring
0.5 mm long and 1.0 mm wide. The through holes 2 were arranged such
that the respective sides of the through holes 2 and the respective
columns formed by the through holes 2 are oriented at an angle of
45 degrees with respect to the respective sides of the polyimide
sheet 1.
[0088] In addition, a beryllium copper plate having a thickness of
30 .mu.m was etched, leaving consecutive beams having a width of
0.12 mm unetched in which contact springs were to be formed.
[0089] Then, the etched beryllium copper plate was sandwiched
between the two polyimide sheets mentioned above, and bonded by
thermocompression bonding. The thickness of the bonded sheet was
approximately 0.15 mm.
[0090] Subsequently, one end of each of two beams left in a
rectangular through hole was cut by pressing and bent in the middle
thereof to form it into a cantilever of a predetermined shape.
Thereafter, nickel/gold plating was conducted to make the contact
sheet in accordance with the present invention shown in FIG. 5.
[0091] When an integrated circuit having spherical terminals was
mounted on a mounting board via the foregoing contact sheet, an
oxide film was effectively removed and stable electrical conduction
was obtained. Moreover, no crushed distal end portions of the
spherical terminals were observed.
Third Embodiment
[0092] Two contact sheets were produced in the same manner as in
Example 1.
[0093] Then, an adhesive film was provided with through holes
having the same shape and the same size with the same pattern as
the contact sheets. That is, a total of 529 through holes having a
rectangular shape of 0.5 mm in length and 1.0 mm in width, 23
columns.times.23 rows, at 1.0-mm pitches. The adhesive film was put
between the two contact sheets so that the contact springs might be
symmetrical with the adhesive film being centered and subjected to
thermocompression bonding to obtain a two-ply contact sheet.
[0094] A single contact sheet had a displacement of about 0.3 mm,
while the two-ply contact sheet had a displacement of about 0.6 mm,
which was twice larger.
[0095] When an integrated circuit having spherical terminals was
mounted on a mounting board via the above two-ply contact sheet,
stable electric conductivity was obtained.
[0096] When the contact sheets in accordance with the present
invention are used as contact boards for integrated circuits having
spherical terminals, oxide films are removed and reliable
electrical conduction can be secured without crushing distal end
portions of spherical terminals. In addition, since current passing
distances in contact springs are shorter, the contact sheets can be
ideally used for high-frequency test boards or mounting boards. In
particular, the contact sheets in accordance with the present
invention are able to secure reliable electrical conduction in
integrated circuits having small-pitch grid arrays that have been
prone to suffer from unstable electrical conduction if a warp
arises.
* * * * *