Socket for printed circuit board

A socket for a printed circuit board which includes a housing having an insertion opening for receiving the printed circuit board. This opening is provided between first and second opposed walls wherein the first wall is shorter than the second wall. A plurality of spring contacts having contacts project from both of the walls into the insertion opening and form rows extending along the axis of the insertion opening. A pair of latch arms extend from those portions of said housing which are close to the ends of the insertion opening so they may be pushed outwardly by the sides of the printed circuit board when the printed circuit board is rotated in such a direction as to press the contacts. They are returned to initial positions by virtue of their elastic force when the printed circuit board passes so as to then hold the board in position. Holder members partially project from the first wall and a latch guide arranged between the holder members and the latch arms to prevent the printed circuit board urged by the spring contacts from rotating at an angle more than a predetermined value when the latch arms release the printed circuit boards. The housing and said latch arms are formed of an integral member made of insulating material.

BACKGROUND OF THE INVENTION 
This invention relates to a socket for a printed circuit board, into which 
an edge portion of the printed circuit board can be directly inserted, as 
a plug, to form a direct connector. 
Recently, various direct connectors of low inserting force type have been 
developed to meet the demand for high-density fitting. 
Generally, such a connector of low inserting force type has a plurality of 
spring contacts aligned in a hosing which is made of an insulating 
material and which constitutes a socket. The contact portions of the 
spring contacts are projected into an opening in order to insert a printed 
circuit board called a daughter board. The contact portions are arranged 
in two rows extending along the insertion opening. Between the rows of the 
contact portions there is provided a clearance for accommodating an edge 
portion of the printed circuit board. The contact portions of one row are 
arranged in offset fashion with respect to those of the other row, in the 
depth direction of the insertion opening, i.e. the direction in which the 
printed circuit board is to be inserted. When the printed circuit board is 
inserted, one surface of the edge portion contacts the contact portions of 
both rows, at a position close to the top of the edge portion, and the 
other surface contacts them at a position far therefrom. 
When the edge portion of the printed circuit board is inserted into the gap 
between the contact rows and the printed circuit board is rotated, moving 
the contact rows away from each other, the contact portions of the spring 
contacts are displaced. Due to the spring force biasing the contact 
portions toward their initial positions, the contact portions reliably 
contact the wires, respectively, when arranged at the edge portion of the 
printed circuit board. 
To reliably fix the printed circuit board to the housing, with the spring 
contacts maintained in the preferable contact with the printed circuit 
board, a latch mechanism is provided which holds the printed circuit board 
in its rotated position and secures the same to the housing. 
Various types of latch mechanism have been developed. 
A latch mechanism described in, for example, U.S. Pat. No. 4,986,765, 
comprises latch members shaped like leaf springs and formed of metal 
plates. These latch members hold a printed circuit board. They have spring 
portions set in the recesses made in the proximal portion of the housing, 
fitting portions projecting downward from the spring portions and inserted 
into an insertion opening of the proximal portion of the housing, and 
latch portions arranged above the spring portions. The latch portions have 
guide portions and cutouts. The guide portions abut on the edges of the 
printed circuit board to bias the spring portions outwards when the 
printed circuit board is rotated. The cutouts receives the side edges of 
the printed circuit board, thereby to hold the printed circuit board at a 
predetermined rotated position. 
U.S. Pat. No. 5,161,995 discloses a latch mechanism comprising latch 
members which are shaped like leaf springs and formed of metal plates, 
like those described above. Each latch member has a fitting portion and a 
latch portion. The fitting portion is arranged at the lower side of spring 
portions, and the latch portion at the upper side thereof. The fitting 
portion has a pair of U-shaped fitting arms wound around a support pole 
positioned near the insertion opening of the printed circuit board. The 
fitting arms make an effect supporting a reaction force of the springs. 
Furthermore, the latch portions form guide surfaces for engaging with the 
edge of the printed circuit board and for biasing the spring portions 
outward when the printed circuit board is rotated, and engaging walls for 
engaging with one surface of the printed circuit board to prevent the 
printed circuit board from returning. 
In either latch mechanism described above, the printed circuit board can 
easily be held or released, taking advantage of the characteristics of the 
metallic leaf springs. 
Either type of the latch mechanism can be further improved in view of the 
fact that each latch members is formed of a metal plate. 
While the printed circuit board is being fitted and rotated, the latch 
members are bent against the spring force, sliding along the guide 
portions or guide surfaces of the latch portions. A coated layer or an 
insulated substrate of the printed circuit board may therefore be damaged 
by the contact with the latch members or its sliding operation. 
Particularly, if the printed circuit board is relatively large or if more 
spring contacts are used because the printed circuit board has high 
density, the force these spring contacts generate will increase. 
Therefore, if the latch members are formed large enough to withstand the 
force, a greater force is required to bend the latch members. This 
increases the possibility that the printed circuit board is damaged. 
At the time the latch members release the printed circuit board, it is 
desirable that the printed circuit board is made to jump and be reliably 
prevented from falling out of the socket due to the bias. 
SUMMARY OF THE INVENTION 
This invention has been made in consideration of the above. Its object is 
to provide a socket for a printed circuit board, which has no metal 
members exposed and which can easily and reliably hold and release a 
printed circuit board without damaging the circuit even if it has many 
spring contacts. 
A socket for a printed circuit board according to this invention comprises: 
a housing having an insertion opening for receiving the printed circuit 
board, said opening provided between a pair of opposing walls; a plurality 
of spring contacts having contacts projecting from at least one of the 
walls into the insertion opening and forming rows extending along the axis 
the insertion opening; a pair of latch arms extending from those portions 
of said housing which are close to the ends of the insertion opening, to 
be pushed outwards by the sides of the printed circuit board when the 
printed circuit board is rotated in such a direction as to press the 
contacts, and to be returned to initial positions by virtue of their 
elastic force when the printed circuit board passes, so as to hold the 
printed circuit board against an urging force of said spring contacts; 
holder members projecting from the other of said walls, for preventing the 
printed circuit board urged by the spring contacts from rotating at an 
angle more than a predetermined value when the latch arms release the 
printed circuit board. The housing and the latch arms are formed of an 
integral member made of insulating material. 
It is desirable that the holder members be arranged in the vicinity of the 
latch arms, and that one of said walls project beyond said holder members. 
When the printed circuit board is inserted into the insertion opening of 
the housing, the contacts come into contact with conductive portions 
arranged an edge portion at a proximal side of the printed circuit board. 
When the printed circuit board is rotated, pressing these contacts, 
against an urging force of the spring contacts, the latch arms are moved 
outwards, guided by the printed circuit board. As the printed circuit 
board is further rotated, beyond the latch arms, the latch arms return due 
to their elastic force, holding the printed circuit board. To release the 
printed circuit board, the latch arms are moved outward. Now released from 
the latch arms, the printed circuit board is rotated around its proximal 
end by the bias of the spring contacts. As long as it is held by the 
holder members, the printed circuit board projects from a wall of the 
housing while being rotated at a predetermined angle. 
When the holder members are arranged near the latch arms, the side of the 
printed circuit board are held. When one of the walls projects beyond the 
holder members, the wall extending along the longitudinal direction of the 
insertion opening is entirely exposed.

DETAILED DESCRIPTION 
FIGS. 1 to 6 show a socket 10 for a printed circuit board according to an 
embodiment of this invention. As shown in FIG. 1, the socket 10 for a 
printed circuit board comprises a housing 14 having many spring contacts 
12 arranged at predetermined intervals. A pair of latch arms 16 extend 
from both end portions of the housing 14, respectively, and a pair of 
support arms 18 extend therefrom. The support arms 18 support latch guides 
20 respectively, as will be described below. The latch guides 20 guide the 
latch arms 16. The housing 14, latch arms 16 and support arms 18 are 
formed as an integral member, made of, for example, an insulating material 
such as LCP (liquid crystal polymer). Reference numeral 22 denotes a 
polarity key, which prevents the erroneous insertion of the printed 
circuit board 8 (see FIGS. 3 and 5). 
As shown in FIG. 2, the housing 14 has a pair of opposing walls 24 and 26 
which are arranged at the upper and lower sides, respectively. Between the 
walls 24 and 25 there is formed an insertion opening 28 for receiving the 
printed circuit board 8. The latch arm 16 is bonded to the lower wall 26, 
at a part close to the longitudinal end portion of the insertion opening 
28. The upper surface at the side of the insertion opening 28 is arranged 
at almost the same level as the upper surface of the lower wall 26. 
Therefore, the latch arm 16 has a structure which can be easily curved, 
with a sectional area smaller than that of the support arm 18. On the 
other hand, the support arm 18 has a comparatively rigid structure. 
The socket 10 for a printed circuit board according to the embodiment is 
mounted on a surface of the mother board (not shown) in a horizontal 
state, with the insertion opening 28 opening sideways. A positioning 
projection 13 is provided at the housing 14. In addition, the socket is of 
the type called DIMM (Dual in-line Memory Module), so classified in terms 
of the fashion of arranging the contacts. 
Contact grooves 30a opening toward the insertion opening 28 are formed at 
the upper wall 24, with a predetermined distance. A holder member 15 
projects from a part which is close to each latch arm 16. This member 15 
is provided to prevent the printed circuit board 8 from rotating at a 
predetermined angle when the printed circuit board 8 is detached as will 
be described below. The member 15 can be formed entirely at the wall 24 
along a contact row. It is preferable to provide the holder members 15 
only at both side portions, respectively, to expose the lower wall 26 as 
much as possible and facilitate the insertion of the printed circuit board 
8. Other contact grooves 30b opening toward the insertion opening 28 are 
also formed at the lower wall 26, spaced apart from each other, and the 
lower wall 26 projects to a position longer than the holder members 15 of 
the upper wall 24. 
The contact grooves 30a of the wall 24 and contact grooves 30b of the wall 
26 are alternately arranged in the axial direction of the insertion 
opening 28. The spring contacts 12 are fitted in the respective contact 
grooves 30a and 30b. The spring contacts 12 shown in FIG. 3(A) are fitted 
in the contact grooves 30a, and the spring contacts 12 shown in FIG. 3(B) 
in the contact grooves 30b. Contacts formed by stamping a plate member of, 
for example, copper alloy can be used as these spring contacts 12. 
As shown in FIGS. 3(A) and 3(B), the spring contacts 12 have fitting 
portions 33 fitted in the housing 14. Contacts 32a and 32b are supported 
at the fitting portions 33 through spring portions 36a and 36b. The spring 
contacts 12 are inserted from the back of the insertion opening 28, i.e. 
from the left side of the housing 14, as shown in FIGS. 3(A) and 3(B). 
Their fitting portions 33 are fitted in fitting apertures 34 formed at the 
lower wall 26. Small projections 35 formed at the fitting portions 33 
prevent the spring contacts from falling out of the fitting apertures 34. 
The contacts 32a are arranged together with the spring portions 36a, in 
the contact grooves 30a of the upper wall 24, as shown in FIG. 3(A), and 
project from the contacts 30a into the insertion opening 28. The contacts 
32b are arranged together with the spring portions 36b, in the contact 
grooves 30b of the lower wall 26, as shown in FIG. 3(B), and project from 
the contacts 30b into the insertion opening 28. Clearances are provided 
between the connects 32a and 30b, and bottom walls of the contacts 30a and 
30b. Terminal portions for connecting to a mother board project from the 
back of the housing 14. 
The contacts 32a and 32b of the spring contacts 12 form rows of contacts, 
which extend along the axis of the insertion opening 28, in the insertion 
opening 28. The contact rows are arranged in an offset fashion with 
respect to the inserting direction E of the printed circuit board 8. When 
an edge portion of the printed circuit board 8 is inserted into the 
insertion opening 28 and the circuit board 8 is rotated in the direction 
of an arrow R, the contacts 32a and 32b are pressed by the edge portion. 
The spring portions 36a and 36b bias the respective contacts 32a and 32b 
toward their initial positions. Due to the spring force, the contacts 32a 
and 32b are pressed onto the wire portions arranged at the edge portion, 
reliably contacting the wire portions. Further, due to the contact rows of 
this offset arrangement, a moment exerting in a direction inverse to the 
arrow R is applied to the printed circuit board 8. 
FIGS. 4(A) and 4(B) show a latch mechanism for retaining the printed 
circuit board 8 receiving this moment, at each of the side edge portions 
in its width direction. Since the latch mechanisms for retaining the side 
edge portions have the same structure, only one of them will be explained. 
The latch mechanism of this embodiment comprises the latch arm 16 extending 
from the housing 14, the support arm 18 and the latch guide 20 fitted in 
the support arm 18 to guide the latch arm 16. 
As shown in FIG. 4(A), the latch guide 20 is formed of one sheet of the 
plate member of, for example, copper alloy. The latch guide 20 has a 
fitting portion 40 fitted in a top portion of the support portion 18, a 
guide portion 42 which is bent almost vertically from one end of the 
fitting portion 40, and a spring portion 44 which is bent almost inverse 
from the other end of the fitting portion 40. An L-shaped engaging member 
46 projects from the upper edge portion of the fitting portion 40, and a 
fixing foot 48 for fixing at a mother board by, for example, soldering, 
projects from the lower edge portion thereof. The guide portion 42 has a 
rectangular plate shape in which the edge portions arranged above and 
under the guide portion form the guide edge portions. Projections 43 
project laterally from the top portion of the guide portion. The spring 
portion 44 arranged in a clearance between the latch arm 16 and support 
arm 18 has a curving portion 50 and can abut on the latch arm 16 through 
the curving portion 50 when the latch arm 16 is curved. 
As shown in FIG. 5, the side of the latch arm 16 has a concave 52 at the 
top of the support arm 18, for containing the fitting portion 40. Further, 
a slot 54 into which the engaging piece 46 is inserted from the top end 
thereof so that it can be fixed is formed. A cutout portion 58 contains 
the fixing foot 48 and a cutout portion 60 contains an engaging projection 
62 which projects from the latch arm 16. 
The latch arm 16 has two protruding portions 64 at its top end as shown in 
FIG. 4. A concave 66 for containing the curving portion 50 provided at the 
spring portion 44 of the latch guide 30 is formed at the side facing the 
support arm 18. The engaging projection 62 projects upward from the upper 
surface of the latch arm 16, and also from the side of the latch arm 16 
toward the support arm 18. A cam portion 68 inclining inwards is provided 
at the upper side of the engaging projection 62. A fitting portion 70 for 
fitting the side edge of the printed circuit board is provided at the 
lower side thereof. An ear portion 72 (FIG. 2) is provided at the side of 
the support arm 18 of the engaging projection 62. When the ear portion 72 
is operated, the fitting portion 70 cam curves and bends the latch arm 16 
between the engaging position (shown in FIG. 1) and the releasing position 
(shown in FIG. 6). At the engaging position, the printed circuit board is 
held. At the releasing position, the engagement is released. 
When the latch guide 20 is fitted in the support arm 18, the engaging piece 
46 is matched with the slot 54 and the latch arm 20 is inserted into a 
clearance between the support arm 18 and latch arm 16, as shown in FIG. 
4(A). The spring portion 44 and curving portion 50 are guided into the 
concave 66 of the latch arm 16, and the fitting portion 40 is arranged in 
the concave 52 (FIG. 5) of the support arm. In this state, the engaging 
piece 46 engages with the interior of the support arm 18 inside the slot 
56 and strictly holds the latch guide 20. At the same time, the fitting 
portions abuts on the side surface of the containing concave portion 52. 
The protruding of the containing concave portion 52. The protruding 
portions 64 of the latch arm 16 abut on the upper and lower guide edges of 
the guide portion 42. The projections 43 prevent the latch guide from 
moving away from the support arm 18. A clearance is formed between the 
curving portion 50 of the spring portion 44 and the bottom surface of the 
concave portion 66 containing the curved portion, in the state of fitting 
with the latch guide 20. 
FIG. 6 shows the operations of the latch mechanism formed in the above 
manner. 
When the printed circuit board 8 inserted into the insertion opening 28 of 
the housing 14 is rotated and abuts on the engaging projections 62 of the 
latch arms 16, the cam portions 68 provided at the engaging projections 62 
bias the latch arms 16 in the direction of arrows 0. Since the latch arms 
16 do not contact the spring portions 44 of the latch arms 20, they 
immediately start moving from the engaged positions shown in FIG. 1 and 
the projections 64 slide along the guide edges of the guide portions 42. 
As the printed circuit board 8 is further rotated, the latch arms 16 move 
to the support arms 18, pressing the spring portions 44. The latch arms 16 
are thereby opened. As the printed circuit board 8 is further rotated and 
moved beyond the cam portions 68, the printed circuit board 8 abuts on the 
upper surfaces of the latch arms 16, 16 and is prevented from moving 
excessively. The latch arms 16 are returned to the engaged positions due 
to their own elastic force and the spring force of the latch guides 20. 
The engagement portions 70 thereby engage with the side edges of the 
printed circuit board 8, holding it at the rotating position. 
The spring portions 44 are provided at the latch guides 20 in this 
embodiment. The latch arms 16 can be immediately returned even in the 
state in which the printed circuit board 8 abuts on the upper surfaces of 
the latch arms 16. 
When the printed circuit board 8 is detached, the latch arms 16 are moved 
to the releasing positions shown in FIG. 6, in the directions of the 
arrows 0 by means of the ear portions 72. The engagement portions 70 (FIG. 
4) of the engaging projections 62 release the engagement with the printed 
circuit board 8. The printed circuit board 8 is rotated such that it moves 
away from the latch arms 16, due to the urging force of the spring 
contacts 12, finally abutting on the holder members 15 provided at the 
wall 24 of the housing 14. The board 8 is held, not falling out of the 
insertion opening 28. At this time, the printed circuit board 8 is held 
and retained without damage, even when the members 15 abuts on the 
portions which are close to the proximal end portion of the printed 
circuit board 8 and where the side edges thereof, i.e. circuits are not 
arranged and when a great moment applies due to the urging force of the 
spring contacts 12. 
When the latch arms 16 move between the engaged position and released 
position, the engaging projections 62 are moved along the flat surface of 
the printed circuit board 8 since the projection 43 are guided on the 
guide edges formed at the edges of the guide portions 42. The engagement 
portions 70 of an insulating material are thereby engaged smoothly with 
the side edges of the printed circuit board 8. In addition, a force of the 
curving or twisting direction, which applies from the printed circuit 
board 8 to the latch arms 16 through the engagement portions 70 can be 
transmitted to the support arms 18 through the guide portions 42 and 
fitting portions 40, and further to the mother board through fixing 
portions 48. Therefore, it is possible to hold the printed circuit board 8 
very firmly while maintaining the curving facility of the latch arms 16. 
Moreover, since the latch guides 20 made of metal are contained between 
the latch arms 16 and support arms 18, the metal portions are not exposed 
to the outside and the safety of the daughter board, etc. can be thereby 
secured. 
As described above, according to the socket for a printed circuit board, of 
this invention, even if the number of spring contacts are increased, it is 
possible to easily and certainly detach the printed circuit board without 
damaging it, due to members of insulating material.