Note: Descriptions are shown in the official language in which they were submitted.
i731~
CONNECTOR SYSTEM
The present invention relates to a connector
system for connection of leadless large scale integrated
circuit (LSI) devices to a printed circuit board or to
other termination means and comprises a leadless ceramic
carrier, a leaded socket and a cover member. Contact is
made between the pads on the leadless LSI carrier and a-
printed circuit board through contact elements carried
by the leaded socket.
Semiconductors and printed circuitry have greatly
0 affected the electronic industry. The increase in circuit
density in electronic devices achieved thereby has stepped
up the demand for denser termination and contact patterns.
Recent advances in LSI technology has made it possible to
produce electr3nic circuitry which is so dense that a single
chip may contain from 20,000 to 50~000 transitors.
For a number of years, the dual in line (DIP)
package configuration has been the package of choice in the
; electronic industry. Designs with up to 6~ leads have been
used, but the most popular si~es have 40 pins or less. The
increased capability of LSI technology and the accompanying
;ncreased system complexities have increased the demand for
packages with greater than 40-pin counts. The DIP comprises
a main body which houses the integrated circuit and has two
parallel rows of leads or "legs" coming off both sides of
the bodY.
Mounting of the DIP on a printed circuit board has
traditionally been accomplished by soldering the legs
7~
-- 2
directly to the board or by being plugged into a socket
which has been soldered into place on the board. I~hile
soldering provides very reliable gas tight electrical
connections, it also makes assembly and removal of the
package difficult due to the necessity of applying heat.
The heat necessary to form the solder connection is quickly
conducted through the leads into the integrated circuit
package which may cause overheating thereof. Overheating
can cause cracks in the ~lass seal and can damage the
integrated circuit. Heat also can warp and/or cause delami-
nation of the printed circuit board. The application of heat
is relatively easy to control during initial assembly of
the circuit board under factory conditions. However, many
costly elements and wir;ng board assemblies have been
destroyed by the application of excessive heat at installa-
tion sites.
Another package, the leadless carrier, offered
a number of advanta~es over the traditional DIP. First,
there are no legs which means lower initial cost and higher
manufacturing yields, Second, leadless carriers are
significantly smaller than equivalent DIPs which thus per-
mits higher packaging densities and shorter lead lengths.
Just as with DIPs, unsoldering a leadless carrier
at an installation site is Very undesirable. Due to the
problems of replacement inherent with solder connections,
many types of demountable connectors have been developed
which do not require the use of heat in the formation of
the electrical connections. These connectors employ what
may be called pressure contacts for the formation of the
i7~
-- 3
electrical connections.
In general, connectors which are soldered in
place require solder leads or legs for the connector and
require minimum contact centers of about 0.10 inch (2.54 mm.)
to avoid solder bridging across adjacent pads on the circuit
board. Connection pads on the carrier may be formed either
along the edge, top or bottom. In all cases, however, the
pluggable connection is made by pressing individual metal
contacts against pads on the carrier. The need for indivi-
dual metal contacts has meant that the connector must
inevitably be large enough to accommodate and separate each
of the individual contacts. The contacts themselves must
be large enough to supply adequate spring force to insure
a good electr;cal connection. In addition to these con-
straints, the precision stamping and assembly requirementshave proved to be quite expensive.
Other problems encountered with the DIPs described
hereinabove have included high thermal resistance, high
pin-to-pin capacitance and hiah lead resistance due to
the long lead lengths especially in the high pin count
DIPs.
The present invention relates to a connector
system for leadless LSI devices and comprises a leadless
ceramic carrier, a leaded socket and a cover member. The
leadless ceramic carrièr serves as a protective package for
the LSI device and for making connection from the LSI
device to the carrier. The leaded socket connects the
pads on the leadless carrier to the circuit board via
contact elements enclosed within the leaded socket. The
~6~
cover member holds the leadless carrier in place and dissipates the heat
which is generated by the LSI in the carrier.
According to a broad aspect of the present invention, there is pro-
yided a connector system for connection of leadless large scale integrated
circuit devices to a printed clrcuit board comprising a reduced size, high pin
count leadless ceramic carrier, a leaded socket having contact elements en-
closed -therewithin and a cover member, said leadless ceramic carrier being
elongate a.nd having closely spaced contact pads on one surface in two stag-
gered rows along each of its longitudinal edges on 50 mil centers, the in-
dividual contact pads in each row being on 100 mil centers, which contact padsare replicated onto the other surface as probing points in a single row along
each o its longitudinal edges on 50 mil centers, said leaded socket compris-
ing interengaging elongate perimetrically equal top and bottom elements
housing contact elements therewithin, said top element having a recess in its
upper face to receive said leadless ceramic c.arrier, said top element having
cavities therein in alignment with the staggered contact pads on said leadless
ceramic carrier and being longitudinally grooved in its lower face for accomo-
dation of the central portion of said contact elements, said bottom element
having caVities therein in alignment ~ith the corresponding cavities in said
top element for insertion of said contact elements therein, said contact
elements having a leg portion, a central portion connected at one end to said
leg portion and at its other end to a spring beam member, and a contact area
joined to said spring beam member, said contact area adapted to make wiping
contact with said contact pads on said carrier, and said cover member being
elongate and having a substantially flat central portion adapted to intimately
contact the undel~lying surface o~ said leadless ceramic carrier and end portions
wnich are slightly outwardly angled joined to depending end walls having an in-
turned lip at its free ends, said lip adapted to engage an edge of said bottom
elemen~ to thereby latch said cover member to said leaded socket.
~ -4-
The invention will now be described in greater detail with refer-
ence to the accompanying drawings, in which:
FIGURE 1 is an exploded perspective view of the connector system
of the present invention;
FIGURE 2 is a sectional end view of the connector system of the
present invention;
FIGURE 3 is an enlarged perspective view of the contact element of
thepresent invention; and
FIGURE 4 is an enlarged plan view of a portion of the leadless
ceramic carrier of the present invention.
Referring more particularly to the drawings, connector system 10
comprises leadless ceramic carrier 11, leaded socket 20 and cover member 50.
In the illustrated embodiment, leadless ceramic carrier 11 is
fabricated of generally conventional materials and design except for the
areas of (1) size - the carrier 11 is able to reduce the circuit board area
by about 40 percent when compared to conventional DIPs; ~2) contact pad
configuration - twice the number of contact pads 13 is provided in the same
space; and (3) chip capacity - the cavity 12 in a 64-pin package is large
measuring 400 x 400 mils ~10.16 x 10.16 mm.) with a depth of 25 mils (0.635
mm.), thus being capable of accommodating large LSI chips.
Carrier ll is fabricated from any of the high quality ceramics of
the type utilized in the manufacture of DIPs. It has high mechanical
strength characteristics
-4a-
~67~iS
-- 5
achieved in part by the reduction in total length. Carrier
ll for a ~4-pin configuration nominally measures 1.65 x
l.O x 0.085 inches (41.9 x 25.4 x 2.159 mm.) thick, or
approximately 50 percent of the si~e of a comparable 64-pin
5 DIP. The increased mechanical strength results in much
higher yields for the semiconductor manufacturers in that
fewer assemblies are damaged due to handling and testing.
An additional benefit is that there are no leads which can
be bent or damaged during the handling and testing process.
In a 64-pin configuration, carrier ll is pro-
vided with 32 contact pads 13 in two staggered rows along
the edge of each side on one face thereof on 50 mil (1.27
mm.) centers, the individual contact pads 13 in each row,
however, being on lOO mil (2.54 mm.) centers. On its other
15 face, also along the edges, each of the 32 contact pad
traces from the other face is terminated as probe contact
14. The probe contacts 14 along each edge are arranged in
a single row on 50 mil (1.27 mm.) centers.
Carrier ll is also provided with a pair of locat-
ing apertures 15, 16, each aperture being differently
configured for keying so that carrier ll cannot be
incorrectly inserted into the leaded socket 20. The ends
of carrier ll are provided with notches 17, 18, ~or a
purpose to be described, also of slightly differing con-
figurations as can be clearly seen in Figure l.
Leaded socket 20 is formed of a bottom element
21 and a top element 30, Bottom element 21 is generally
rectangular in shape, is formed from insulating material
and is provided with two rows of staggered cavities 22
7~
-- 6
along each longitudinal edge thereof on 50 mil (1.27 mm.)
centers, the individual cavities 22 in each row, however,
being on 100 mil (2.54 mm.) centers. A pair of locating
apertures 23 is formed in bottom element 21, the shapes and
locations of which correspond to the locating apertures 15,
16 provided in carrier 11. The ends of bottom element 21
are each centrally cut away in a rectangular pattern to form
indented edges 25. The bottom of edges 25 are slightly
undercut so that edges 25 are of lesser thickness than the
remainder of bottom element 21. The central portion of
such edges 25 is further cut away in a rectangular pattern
to form notches 26 for a purpose to be described. The
central portion of the bottom sur~ace of bottom element 21
is cut away in a substantially rectangular pattern 27,
leaving, however, lands connected to the surrounding bottom
surface around the locating apertures 23. Located at the
four corners and upon the lands adjacent the locating
apertures 23 are slight protuberances 28 which serve to
space connector 10 from the circuit board.
Top element 30 is also generally rectangular in
shape, formed of an insulating material and is pro~ided
with two staggered rows of cavities 31 along each longi-
tudinal edge thereof on 50 mil (1.27 mm.) centers, said
cavities 31 being somewhat larger than cavities 22 for
a purpose to be described. End walls 32 are provided
adjacent to form a recess 33 for ceramic carrier 11. A
pair of locating posts 34, 35 is proYided on each surface
of top element 30, the shapes and locations of which corres-
pond to the locating apertures 15, 16 in carrier 11 and 23
~i
ii7~
in bottom element 21, The ends of top element 30, includ-
ing end walls 33 are each centrally cut away in a rectangu-
lar pattern corresponding in dimensions to the cut-away
- in bottom element 21 to form indented edges 36. The
5 central portion of such edges 36 is further cut away in a
rectangular pattern also corresponding to the cut-away
in bottom element 21 to form notches 37 for a purpose to
be described. Top element 30 is further provided with a
central aperture 38 to accommodate the cover seal 19 on
carrier 11 which seals the LSI device in cavity 12.
Longitudinal grooves 39 underlying cavities 31 are pro-
vided in the bottom surface of top member 30, as viewed
in Figure 2, to accommodate contact elements 40.
Contact elements 40 are die cut from a thin flat
15 plate of resilient metal such as spring tempered Copper
Nickel Alloy 725, nominally 5 mils (0.127 mm.) thick and
is usually provided with a conductive coating such as a
24K gold cladding over a nickel interliner9 said gold
cladding being about 0.00003 inch (0.00076 mm.) in th;ck-
20 ness, at the contact area 41 of said contact element 40which makes contact with the contact 13 of carrier 11.
As can be clearly seen in Figure 3, contact
element 40 has a generally U~shaped leg portion 42 formed
by bending the flat stock at approximate right angles.
25 The end of leg portion 42 is cut off at an acute angle to
provide a pointed tip. At its upper end, lea 42 is pro-
vided with a pair of lock;ng tabs 43 for engagement with
the walls of cavities 22. The upper end of leg 42 termi-
nates in a pair of tabs 44 which help to rigidify leg 42.
7'~
The central portion 45 of contact element 40
joins leg portion 42 at a right angle at one end. The
other end of central portion 45 is C-shaped and joins
spring beam member 46 which is generally parallel to
central portion 45. Spring beam member 46 is joined at
a right angle to contact area ~1 which is generally J-
shaped.
In a specific illustrative embodiment, using
the above-identified metal plate, the overall length of
contact element 40 is 0.4~5 inch (10.795 mm.) and the
overall width is 0.03 inch (0.762 mm.). The length of
leg portion 42 is 0.3 inch (7.62 mm.) with the legs of
the U being 0.015 inch (0.381 mm.). The central portion
45 is 0.125 inch (3.175 mm.) long and the height of the
C is 0.05 inch (1.27 mm.). The spring beam member is
0.08 inch (2.032 mm.) long and the leg o~ the J-shaped
contact area is 0.075 inch (l.90S mm.), the curved por-
tion thereof having the gold cladding applied thereto
being 0.03 inch x 0.035 inch (0.762 x 0.889 mm.).
As will beclearly seen in Figure 3, contact
e1ements 40 are not completely removed from the plate
stock in the forming process. Instead, a portion of the
plate stock 47 from which contact elements 40 have been
die cut is left attached at the juncture of the central
portion 45 and spring beam mernber 45 so that contact
elements 40 are interconnected together in strip form.
Plate 47 may be scored during the die cutting operation
along the junction lines ~ so that contact elements 40
can be readily separated into individual elements when
desired.
ii7~
Cover member 50 is generally rectangular with a
length substantially equal to the length of carrier 11 and
is just sufficiently narrow to avoid electrical contact
witn the rows o~ probe contacts 14 on the sur-face of
carrier 11, which~ as earlier described, are in a single
row along each longitudinal edge thereof and is fabricated
from a copper alloy with very hi~h thermal conductivity
properties, Preferably~ cover member 50 is spring tempered
and is provided with a heat conducting finish coat such as
a nickel plate. The top surface of cover member 50 is
divided into three approximately equal portions 51, 52 and
53. The central portion 52 is substantially flat so that
intimate contact can be made with the surface of carrier 11
immed;ately over the LSI chip contained therein. Central
portion 52 is provided with a longitudinal rib 54 adjacent
and along each of its outer edges to lend strength and
rigidity to cover member 50.
Each of the outer end portions 51 and 53 of
cover member 50 is bent at a sliqht outward upward angle
at its juncture with central portion 52, for a purpose to
be described. A plurality of transverse slots 55 is
provided in each end portion 51, 53.
Depending ~rom the outer end of each end portion
Sl, 53 is an end wall 56 having a length equal to the
combined thickness of carrier 11 and leaded socket 20,
less the depth of the undercut along the bottom of edge
25, and having a width equal to indented edges 25 and 36.
A central rectangular aperture 57 is cut out at the junction
of each end portion 51, 53 with depending end walls 56,
-- 1 o
corresponding in size and location to the cut-aways in
edges 25 and 36. An inwardly turned lip 58 is attached
to the free end of each end wall 56.
The connector system 10 of the present invention
is assembled by first mounting the chip into the cavity 12
of carrier 11 in the conventional manner. ~ire bond con-
nections are then made from the chip to contact points pro-
vided along the perimeter of the cavity 12, again in the
conventional manner after which cover seal 19 is attached.
Leadless socket 20 is assembled by first inserting an
interconnected strip of contact elements 40 into cavities
22 in bottom element 21. After contact elements 40 are
firmly seated in cavities 22, the connecting strip of
plate stock 47 is broken off along lines 48 leaving an
individual contact element 40 in each cavity 22. Top
element 30 is then assembled onto bottom element 21, the
locating posts 34 and 35 and complementarily shaped
locating apertures 23 insuring proper orientation of top
element 30 to bottom element 21. In this assembly process,
central portion 45 and spring beam member 46 of contact
elements 40 are received w;th;n longitudinal grooves 39
in top element 30 and J-shaped contact area 41 thereof
protrudes through cavities 31, as clearly shown in Figure
2. If desired, the two parts of leaded socket 20 may be
sealed together as by sonic or heat welding or with a
su;table adhesive.
The thus assembled leaded socket 20 is placed
onto a printed circuit board (not shown) with leg portions
42 protruding through apertures in the circuit board which
67'~3
is then wave soldered in the conventional manner. It
should be noted that leaded socket 20 is mechanically
keyed by means of the staggered arrannement of leg por-
tioils 42 in cavities 22 and the circuit board hole pattern
such that it cannot be improperly inserted into the cir-
cuit board, After the circuit board is cleaned, lead-
less ceramic carrier 11 is then placed into recess 33 with
the cavitiy 12 facing downwardly, as viewed in Figures 1 and
2. Again, locat;ng posts 34 and 35 and locating apertures
15 and 16 make it impossible to insert the carrier 11 into
the socket 20 with any other orientation than the proper
orientation. Finally, cover member 50 is placed over
carrier 11 and snapped onto socket 20, end walls 56 fitting
within the rectangular cut-outs in the top element 3Q and
bottom element 21 with inturned tip 58 enqaging the cut
away portion along the bottom of edge 25. Tension is
maintained between inturned lip 58 and edge 25 by the
upwardly bent end portions 51 and 53 of cover member S0.
Carrier 11 is thus firmly pressed downwardly in recess
33 and contact pads 13 are pressed onto the protruding
J-shaped contact areas 41 of contact elements 40. Electri-
cal connection is made when the J-shaped contact area 41
of contact element 40 wipes against contact pad 13 on
carrier 11. The wiping contact is enhanced and maintained
through the action of spring beam member 46 which also
effects electrical separation of the contact area 41 of
adjacent contact elements 40 by a bending action upon
contact with contact pad 13, As viewed in the left lower
corner of Fi9ure 2, contact area 41 of the contact element
40 closest to the viewer would bend to the ri~ht and the
7~3
- 12 -
contact element distal to the viewer would bend to the
left. Cavities 31 in top element 30, it will be remembered,
were sized to be somewhat large to accommodate this bending
action of J-shaped contact area 41. Electrical connection
is also enhanced by the gold cladding on contact area 41.
When it is desired to remove carrier 11 from socket 20
for diagnostic, "debugging", maintenance or other purposes ?
a screwdriver blade is inserted perpendicularly into
aperture 57 in cover member 50 and also into aligned
notches 26 and 37; slight outward pressure against end
wall 56 will disengage inturned lip 58 from edge 25.
Oover member 58 can then be lifted off and carrier 11
removed.
The connector system 10 of the present invention
makes it possible to provide a high pin count package to
take advantage of the advances in LSI technology without
increasing the physical size oF the package. The connec-
tor system of the present system is, in fact, about 60
percent smaller than a comparable DIP.
The electrical performance of an electronic
package is, of course, affected by its size and geometry.
Package geometry dictates trace lengths and uniformity of
trace widths. Lead resistance and inter-lead capacitance
are directly affected but can also vary due to different
path lengths. For example, the lon~est trace on a typical
64-lead DIP is over six times as long as ihe corresponding
trace on one type of leadless carrier. The ratio of
longest to shortest trace on a 64-lead DIP is 7:1 while
the ratio is S:l for the leadless carrier of the present
7~
- 13 -
invention. These unequal trace lengths and long electri-
cal paths of DIPs have severely limited their eFfective
use in high performance applications. In general, shorter
trace lengths result in lower resistance and inter-lead
capacitance which permits faster switching times and
overall improved performance. The maximum lead resistance
of the leads in the present connector system is 0.3 ohm
and the maximum lead-to-lead capacitance is less than
3 pfd as compared to values of 1.1 ohm resistance and
6.6 pfd capacitance in a comparable DIP.
In the past, high pin count packages, especially
the DIPs, suffered from the force required to insert the
package into or remove same from a socket. This resulted
in bent or broken leads, broken packages and damaged
sockets. As a result, only a limited number of insertions
of the package into the socket was possible before per-
manent damage occurred, The system of the present inven-
tion has "~ero insertion force" as well as "zero extraction
force" so a large number of insertions or removals may be
safely accomplished.
It will be recalled that the leadless chip
carr;er in the present invention makes contact with the
contact elements on the bottom side and a set of probe
contacts is provided on the opposite or top surface of the
carrier. This arrangement makes it possible to make
direct electrical measurements at any contact point while
the chip is in operation in situ, a very valuable diagnos-
tic and maintenance tool.
Cover member 50, in addition to securely holding
the leadless chip carrier 11 into intimate electrical
contact in socket 20, also serves as a heat dissipating
element through the material of the cover member making
intimate contact with the surface of carrier 11. Heat
dissipation can also be enhanced bv, for example, providing
cooling fins~ etc. on the central portion 52 of cover member
50. The thermal resistance of the connector system of the
present invention is 35C. per watt which is extremely
low when considerina the reduced circuit board area occupied
by the system.
