Abstract:
A connector includes an insulative housing and rows of contacts with downwardly projecting lower ends soldered to contact pads on a circuit board, which assures engagement of all contact lower ends with all contact pads despite tolerance buildup due to housing warping. Each contact has upper and lower contact elements ( 50, 52 ) biased apart by a coil spring ( 54 ). When the connector is placed on a circuit board ( 14 ), the connector is moved down until spacers ( 92 ) on the housing lower surface engage the circuit board and cause the lower ends of all contacts to be upwardly deflected to firmly engage the contact pads for reliably soldering to them. One of the contact elements has a pair of beams ( 110, 112 ) that are slideably engaged in a cylindrical hole ( 130 ) in the other contact element to assure good electrical contact and to avoid large inductances that would arise if most currents passed through the coil spring.

Description:
BACKGROUND OF THE INVENTION 
     One type of surface mount connector includes an insulative housing and rows of contacts mounted in the housing. The contacts have lower ends that are connected to contact pads on the upper face of a circuit board, as by soldering thereto. One way to cause the lower ends of all contacts to engage all corresponding contact pads is to precisely machine the lower ends of all contacts so they all lie in the same plane. Then the connector can be pressed down against the circuit board and solder connections made by vapor phase soldering. 
     One problem encountered with this approach is that the housing sometimes warps, resulting in some contacts lying close to but not against the corresponding contact pads, resulting in poor solder connections. In addition, the cost for precisely machining the lower ends of the contacts to lie in a single plane, can add expense. The upper ends of the contacts often must be resiliently deflectable downwardly to enable connection to another connector or pads of another circuit board by merely pressing them against the upper ends of the contacts. A connector that minimized the cost of connectors of the above-mentioned type and which enabled the connectors to hold a large number of contacts without danger of poor solder connections due to warping of the housing, would be value. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a connector system is provided of the type wherein a connector has contacts depending from a connector housing for pressing against contact pads of a circuit board to solder thereto, which assures reliable solder connections despite the use of a long connector housing that may warp, and which minimizes the height and cost of the connector. Each contact has a lower end that is spring-biased downwardly so the lower face of the contact lower end lies at an initial position below the housing main lower surface. The connector housing includes a plurality of spacers that depend from the housing main lower surface by less than the initial projections of the contact lower ends. Accordingly, when the connector is pressed down against a circuit board and fixed to the circuit board, the lower ends of the contacts are resiliently deflected upwardly to a level even with the spacer lower surfaces, thereby assuring that each contact firmly engages one of the contact pads on the circuit board. 
     Each contact includes upper and lower contact elements and a spring that biases them apart. The housing has passages with conical shoulders that engage corresponding shoulders of the upper and lower contacts to prevent the contacts from moving completely out of the passage. The lower contact element has a narrow upwardly-extending post with a slot dividing it into a pair of beams. The upper contact element has a cylindrical hole, and the beam upper ends lie in the cylindrical hole and are biased apart to make firm contact with the walls of the cylindrical hole, thereby assuring good electrical connection between the upper and lower contact elements. The spring is a helical spring that surrounds the post. By assuring that most current flows through the post instead of the helical spring, applicant avoids the high inductance that would occur if most current passed through the spring. 
     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded top isometric view showing a connector of the present invention mounted on a lower circuit board, and showing a mating upper circuit board positioned to be lowered against upper ends of contacts of the connector. 
     FIG. 2 includes an exploded bottom isometric view of the connector and a top isometric view of a portion of the lower circuit board of FIG.  1 . 
     FIG. 3 is a sectional view of the connector of FIG. 2, showing it approaching the lower circuit board of FIG.  2 . 
     FIG. 4 is a sectional view similar to that of FIG. 3, but with the connector fully lowered against the lower circuit board and with its contacts soldered to circuit board pads, and also showing the upper circuit board of FIG. 1 pressed downward against a contact. 
     FIG. 5 is a sectional view taken on line  5 — 5  of FIG.  3 . 
     FIG. 6 is an exploded isometric view of the upper and lower contact elements of the connector of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a connector system  10  which includes a connector  12  mounted on a circuit board  14 , and showing a second mating connector in the form of a circuit board  16 . As shown in FIG. 2, the first circuit board  14  has multiple contact pads  20  arranged in a plurality of rows  21 - 24 . The contact pads are usually very thin (e.g. more than 0.001 inch), so their upper surfaces are substantially flush with the rest of the circuit board. The connector  12  has corresponding contacts  26  arranged in corresponding rows  31 - 34 . In practice, the connector  12  is mounted on the circuit board  14  and contact lower ends  36  are soldered to the contact pads  20  on the circuit board. The connector is fixed in position on the circuit board by a plurality of board mounts  40  that are received in mount holes  42  of the circuit board. 
     In order for the contact lower ends  36  to be soldered to the contact pads  20 , the contact lower end surfaces  38  must engage the contact pads  20 , usually with a thin disc of soldering material between them which is heated to complete the soldering operation. In FIG. 2, there are sixty contacts arranged in four rows and thirty staggered columns. One approach of the prior art was to fix at least the lower portions of the contacts in the connector and to precisely machine the contact lower surfaces  38  so they all lay in a common plane. One problem encountered with this approach is that the molded plastic housing  44  which holds the contacts, can warp between the time when the manufacturer machines the lower faces of the contacts and the time when the customer mounts the connector on the circuit board. The connector of the present invention assures that all contacts will engage their corresponding circuit board contact pads, despite warping of the housing  44 . 
     FIG. 3 shows details of the connector  12  and of the circuit board  14 . Each contact  26  includes upper and lower contact elements  50 ,  52  and a spring  54 . The spring presses against spring-engaging surfaces  56 ,  58  of the contact elements and biases them apart. The insulative housing  44  has upper and lower housing halves  60 ,  62  that are each injection molded. The housing has a plurality of passages  64  that each holds one of the contacts, each passage having upper and lower passage portions  70 ,  72 . The contacts are dropped into the passage portions of one housing half, and the housing halves are then brought together and fixed together. Although the spring  54  urges the contact elements  50 ,  52  apart, they are prevented from moving out of the housing by forming each passage with upper and lower passage shoulders  74 , 76 . Each contact element has a corresponding contact shoulder  80 ,  82 . 
     FIG. 3 shows the connector  12  with lower end surfaces  38  of the contact lower ends lying above the circuit board  14 . A solder disc  84  has been placed on each contact pad  20 . Each solder disc  84  includes a mixture of microscopic particles of solder with solder flux. The housing has a main lower surface  94  and has spacers  92  depending from the lower surface. The spacers have lower spaces faces  90 . The connector  12  is lowered against the circuit board  14  until the lower spacer faces  90  abut an upper face  96  of the circuit board. The lower end surfaces  58  of the contacts lie below the level of the spacer faces  90 , so the contact lower elements  52  are deflected upwardly. 
     FIG. 4 shows the connector  12  after it has been firmly pressed down towards the circuit board until the spacer lower faces  90  press against the circuit board upper face, and with the contacts soldered to the contact pads  20 . The lower contact element at  52 A has been deflected upwardly relative to the housing by compression of the spring  54 A. With all contact lower end surfaces or faces  38  pressing down against corresponding contact pads  20 , the soldered discs are heated by the known vapor phase method, to melt the solder flux and solder of the solder discs and produce a solder joint at  100 . 
     FIG. 4 shows that the upper contact elements have upper ends  104  that project above the housing main upper surface  106 . The second mating connector circuit board  16  with contact pads, or conductive traces  102  is shown pressing down against the upper end of the upper contact element  50 A and depressing it by further compression of the spring  54 A. The connector  12  serves to connect the multiple conductive traces  102  on the mating connector  16  with the multiple contact pads  20  on the circuit board  14 . To do this, the upper and lower contact elements  50 ,  52  must be connected together to transmit current such as high frequency signals between them. 
     It would be possible to rely upon the spring  54 A to transmit high frequency signals between the lower and upper elements  52 A,  50 A. However, there are two disadvantages in the use of the spring for this purpose. A low cost high performance spring is commonly formed of stainless steel, which has only moderate conductivity compared to brass alloys used for conducting electricity. In addition, the multiple turns of the spring result in high inductance, which is undesirable for high frequency signals. Applicant assures a low resistance connection between the lower and upper contact elements  52 A,  50 A while minimizing inductance, by the use of a pair of beams  110 ,  112  formed on the lower contact element  52 A. 
     As shown in FIG. 3, the lower contact element is machined with a post  114  that extends upward from the larger diameter lower end  52 . The post has an upper end with a slot  116  that divides the post upper end into the pair of beams. Each beam has a projection  120  that projects radially outwardly with respect to an axis  122  of the contact and passage. The upper contact element  50  is formed with a largely cylindrical hole, or bore  130  that receives the upper ends of the beams. The beams tend to assume a position where the projections  120  are spaced apart by more that the diameter of the bore  130 , so the walls of the bore  130  deflect the beams closer together, thereby assuring pressure contact between the beam projections  120  and the walls of the bore  130 . The beam projections lie in a sliding fit, or in sliding contact, with the walls of the bore so the beams can slide up and down within the bore of the upper contact element, while remaining in low resistance engagement with the upper contact element. The upper and lower contact elements are formed of a low resistance metal such as a low resistance brass alloy, which assures low resistance contact. 
     FIG. 5 shows that the beam projections  120  form large area contact with slide surface portions  140 ,  142  of the walls of the hole  130 . This is achieved by forming the projections  120  with a radius only slightly less (within 20%) than the radius of the bore  130 . 
     FIG. 4 shows the upper and lower housing shoulders  74 ,  76  are conical, and extend at an angle A of about 70 degrees from the horizontal. The corresponding contact element shoulders  80 ,  82  are similarly angled. It would be possible to instead have shoulders extending horizontally, but this would require more expensive machining of the contact elements, and would require a somewhat thicker housing or result in shoulder walls that were not robust against breaking. 
     In a system that applicant has designed, and which is illustrated, the connector housing had an overall length L (FIG. 2) of 46.5 mm (1.83 inches) a width W of 6 mm (0.24 inch) and a thickness T of 44 mm (1.74 inches), and had sixty contacts. Each contact had a flat lower surface with a diameter D (FIG. 3) of 0.84 mm (0.033 inch) and the contacts were spaced apart along each row by 1.5 mm (0.059 inch) with other dimensions being proportional to those given, as is illustrated in FIGS. 3 and 4. 
     Although terms such as “up”, “down” etc. having been used to describe the invention as it is illustrated, it should be understood that the connector can be used in any orientation with respect to the Earth. 
     Thus, the invention provides a connector and connector system, of a type wherein the lower ends of contacts are soldered to contact pads on a circuit board, which assures that all contacts will be reliably soldered to the corresponding contact pads, especially when vapor phase soldering is used, and with the contacts having upper and lower contact elements connected in a low resistance connection of minimum inductance. The insulative housing of the connector has a main lower face and has spacers extending downward therefrom, the spacers having spacer lower faces that engage the circuit board. Each contact has a lower contact element that is spring biased to an initial downward position wherein the lower surface of the contact lies lower than the lower surfaces of the spacers. When the connector housing is pressed downward towards the circuit board, the contact lower elements are resiliently deflected upwardly to lie in the same plane as the lower surfaces of the spacers, thereby assuring that all contact element lower faces engage the corresponding circuit board contact pads, and thereby assuring reliable solder joints. The upper contact element is preferably resiliently biased upwardly but can be downwardly deflected. Although a spring biases the lower contact element downwardly, and usually also biases the upper contact element upwardly, electrical connections between the elements are not primarily through the spring. Instead, the connections are made through a plurality of beams extending from a contact element such as the lower one, the beams being slideably engaged with a surface of the other element, as where a pair of beams on the lower contact element lie in a cylindrical bore in the upper contact element and are biased firmly against the walls of the bore. The lower contact element has a conical shoulder that engages a corresponding conical shoulder of the lower housing half of the connector. 
     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.