ADAPTER FOR USE IN AN APPARATUS FOR TESTING CIRCUIT CARDS

Abstract: An adapter for use in an apparatus for testing circuit cards, said apparatus comprising a set of test contact spots (3) in a certain distribution for application of test signals, comprises contact members (4) arranged to contact electrically conducting places (5) on the circuit card (6) and means (7) for bringing the test contact spots and the contact members into conducting contact with each other. The contact means (7) is formed by an adapter plate, which on a first side comprises first electrically conducting places (9) in correspondence to the actual occurrence of contact members (4) and adapted to be contacted by the latter and which on its other side (10) comprises second electrically conducting places (11) having a distribution corresponding to the distribution of the test contact spots and intended to contact actual ones of said test contact spots. Between first and second electrically conducting places (9, 11) belonging to each other and being present on the two sides of the plate (7) there are electrical conducting paths (12).

Description: ADAPTER FOR USE IN AN APPARATUS FOR TESTING CIRCUIT CARDS FIELD OF THE INVENTION AND PRIOR ART This invention is related to an adapter according to the precharac- terizing part of enclosed claim 1 . Such an arrangement is disclosed in the applicant's own Swedish patent 8704468-1 (458 005). Although this known adapter has functioned well in practice and resulted in a considerable commer¬ cial success, it has, nevertheless, been associated to some defi¬ ciencies, which have become more and more important as the densification of contact places and conducting paths on the circuit cards has proceeded. Since the test contact spots have a certain distribution with an equal distance between test contact spots all over the entire test contact spot area and the density with regard to these test contact spots for practical/economical reasons is lower than that which may be in question for the electrically conducting places on the circuit card, the contact members of the adapter were constructed with flexible portions so that the contact members could be caused, by bending thereof, to contact the test contact spots despite the latter being located laterally displaced relative to the electrically conducting places on the circuit card and those parts of the contact members which contacted these places. Another solution is described in the European patent No. 0 149 776, where pin-like contact members in an adapter extend obliquely through the adapter to establish contact between the test contact spots and the actual electrically conducting places on the circuit card. The intention in the European patent is that the contact SUBSTITUTE SHEET members should extend rectilinearly through the adapter and for this purpose the adapter comprises guide plates provided with holes, through which the contact members extend. The holes pro¬ vided in these plates for a contact member extend rectilinearly, which means that the holes become laterally displaced relative to each other. Independently of whether the contact members extend obliquely as a consequence of bending or an angled position with a maintained rectilinear extent, the oblique position of the contact members causes sources of errors which can not be accepted, in particular not when qualified circuit card products having a high density as far as conducting portions are involved. The oblique position by means of bending or inclination causes the contact members to contact the test contact spots (Swedish patent No. 458 005) or the circuit card (European patent No. 0 149 776) with a contact characteristic dependent upon the oblique position of the contact members. Fur¬ thermore, it is difficult to design the adapter so that those ends of the contact members which are intended to contact the electrically conducting places on the circuit card are so closely located which is desirable as a consequence of the present qualified circuit card manufacturing techniques. According to another proposal according to prior art and falling beside the precharacterizing part of the enclosed claim 1 , one has used a rubber mat to establish an electrical contact between the contact members and the electrically conducting places on the circuit card. Thus, this rubber mat has been imparted electrical conductivity, more specifically by being provided with electrically conducting constituents. In that way the rubber mat became "semi- conductive". However, it turned out that such a rubber mat did not function in practice due to the varying electrical contacting charac¬ teristic as a consequence of conducting paths having different lengths through the semi-conductive rubber material, since the contact members in this known embodiment were not located di¬ rectly opposite to the electrically conducting places on the circuit card but in a predetermined uniform distribution, and as a conse¬ quence of an unsatisfactorily large transition resistance in the contact region between the rubber mat and the electrically conduct¬ ing places on the circuit card. These conducting places are, namely, formed by a metal plating, which often is surrounded by a thicker mask, so that the contact place formed by the plating is somewhat counter-sunk relative to the surrounding external mask surface. SUMMARY OF THE INVENTION The object of the present invention is to provide an adapter having means functioning well from the point of view of electrical contact¬ ing in order to bring the test contact spots and the contact mem- bers in conducting contact with each other. The contact members are, of course, intended to be located in a distribution correspond¬ ing to the electrically conducting places which occur on the circuit card, for which the adapter is prepared, and which shall be con¬ tacted for testing purposes, whereas the test contact spots are located in another distribution, which as a rule probably will be, in practice, uniform over the test contact spot area of the test appara¬ tus. This object is achieved according to the invention in that the con- tact means is formed by an adapter plate, which on a first side comprises first electrically conducting places in correspondence to the actual occurrence of contact members and adapted to be con¬ tacted by the latter and which on its other side comprises second electrically conducting places having a distribution corresponding to the distribution of the test contact spots and intended to contact actual ones of said test contact spots, and that between first and second electrically conducting places belonging to each other and being present on the two sides of the plate there are electrical conducting paths. Thus, the adapter plate will interconnect, in an electrically conduct¬ ing way, the contact members and the test contact spots independ¬ ently of actual differences with regard to location occurring be¬ tween the contact members and the test contact spots. Accord- ingly, the contact members, suitably in the form of pins, may extend mutually substantially parallel so that the oblique positions and inclinations respectively occurring in prior art can be avoided en¬ tirely. According to a preferred embodiment, the adapter comprises a movable disk in accordance with claim 5. In accordance therewith and while observing that which is defined in claim 7, one can obtain an embodiment where a circuit card placed on the movably ar¬ ranged disk is pressed, together with the movably arranged disk, in a direction towards the adapter body so that the first ends of the contact members will project through the holes and in that way get in contact with the circuit card while being guided by the movably arranged disk. This is preferable particularly for the reason that the contact members normally are intended to be realised in the form of very slender and, accordingly, rather sensitive pins. Further preferable features of the invention are the subject matter of the rest of the dependent claims. SHORT DESCRIPTION OF THE DRAWINGS With reference to the enclosed drawings, a more specific descrip¬ tion of an embodiment example of the invention will follow hereun- der. In the drawings: Fig 1 is a partially cut, diagramatical cross-section through a part of an apparatus for testing circuit cards and an adapter intended to be used therewith; Fig 2 is an enlarged detailed view illustrating application of a circuit card against the adapter while establishing contact between the contact members and conducting places on the circuit card; and Fig 3 is a diagrammatical view illustrating a part of the adapter plate viewed from its side turned towards the test contact spots. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In Fig 1 there is illustrated an adapter generally denoted 1 and intended for use with an apparatus 2 for testing circuit cards. This apparatus comprises a set of test contact spots 3 in a certain distribution for application of test signals. The adapter 1 comprises contact members 4 arranged to contact electrically conducting places 5 on the circuit card 6, as appears from Fig 2. Furthermore, the adapter comprises means 7 for bringing the test contact spots 3 and the contact members 4 in conducting contact with each other. The contact means 7 is formed by an adapter plate, which on a first side 8 comprises first electrically conducting places in correspon¬ dence to the actual occurrence of contact members 4 and adapted to be contacted by the latter and which on its other side 10 com- prises second electrically conducting places 1 1 having a distribu¬ tion corresponding to the distribution of the test contact spots 3 and intended to contact actual ones of said test contact spots. Between first and second electrically conducting places 9, 1 1 belonging to each other and being present on the two sides 8, 10 of the plate 7 there are electrical conducting paths 12, which are diagrammati- cally illustrated in Fig 2 and more realistically in Fig 3. The electrical conducting paths 12 extend through holes 13 made in the plate 7. The plate 7 consists preferably of a base plate prepared from an electrically insulating material, on which base plate the electrically conducting places 9 and 11 and the conducting paths 12 have been formed by plating or other deposition of electrically conducting material, normally in the form of metal. The holes 13 are prepared in the plate 7 by boring or other method useful for hole formation, at least parts of the walls of the holes 13 being covered with a conducting material to establish a conducting connection between the electrically conducting places on the two sides 8 and 10 of the plate 7. It is of course realised that the dashed lines present in Fig 2 and intended to diagrammatically illustrate the conducting paths 12 are not intended to mean that the conducting paths are present within the plate 7 even if this would not be impossible. Instead it is intended, in the example illustrated, and also in the normal case, that the conducting paths 12 are provided on that surface on the plate 7 which forms the side 10. The contact members 4 are formed by pins intended to (see Fig 2) contact, with first ends 14, the conducting places 5 on the circuit card and to contact, with second ends 15, the electrically conduct¬ ing places 9 on the side 8 of the adapter plate 7. The contact pins 4 are received in aligned holes in a number of disks 16 included in the adapter 1. These disks 16 are mutually connected by means of suitable fixing means 17 in the form of rivets, bolts or similar and form, accordingly, a body generally denoted 18 of the adapter. It is pointed out that it is not absolutely necessary for the adapter plate 7 to be secured to the body 18 but the adapter plate 7 could be formed by a part included in the adapter 1 but separable from the adapter 1 for the rest. However, the adapter plate 7 is intended, in the example, to be connected to the body 18 for the rest of the adapter 1 by means of the fixing means 17. The adapter comprises a disk 19 movably arranged relative to the body 18 of the adapter, said disk comprising holes 20 (see Fig 2) for penetration by the ends 14 of the contact pins 4 and being pressable, against the action of spring force, in a direction towards the body 18. The adapter comprises means 21 (see Fig 1 ) for restricting movement of the movable disk 19 in a direction away from the adapter body 18. It is preferred that the first ends 14 of the contact pins 4, as is indicated in Fig 1 , are located substantially flush with or inwardly of the external surface 22 turned away from the body 18 when the disk 19 is spaced from the body 18. The restriction means 21 are suitably adjustable for adjustment of the movement end position of the movable disk 19 in a direction away from the adapter body 18. In the example the restriction means 21 are formed by heads of screws 23, said heads 21 being designed complementary to re¬ cesses in the disk 19 so that the heads 21 do not protrude out¬ wardly of the external surface 22 of the disk 19. The screw 23 engages, by means of its thread shaft, with a nut 24 present in a cavity 25 of the body 18, said nut being actuated by means of a pressure spring 26, in particular a screw spring, in a direction towards an end wall delimiting the cavity 25 in such a direction that the head 21 of the screw 23 tends to be spaced as much as possible from the body 18. However, by turning the screw 23 relative to the nut 24 the projection of the screw away from the body 18 and, accordingly, the end position of the disk 19 outwardly away from the body may be adjusted. The nut 24 is secured against rotation. It is understood in practice that several screws 23 and associated nuts, springs and cavities are present for adequate holding and guiding of the disk 19 relative to the body 18. In the example the spring force counteracting pressing of the disk 19 in a direction towards the adapter body 18 is exerted by pres¬ sure springs 27 acting between the body 18 and disk 19, said pressure springs being, for example, arranged about the thread shafts of the screws 23. Circuit cards are often provided with a conductor pattern and con- nection places on both sides. In order to be able to test the conduc¬ tor paths on its two sides in one and the same clamping of the circuit cards, a further adapter 1 with associated test contact spot device may be arranged above the one illustrated in Fig 1 in order to be able to contact a circuit card placed on the disk 19 from above. The adapter 1 intended to be located underneath com¬ prises, just like the adapter intended to be placed on the top, mu¬ tually guiding members 28, for instance in the form of guide rods to adequately locate the two opposite adapters relative to each other. Furthermore, the adapter 1 illustrated in Fig 1 comprises, just like the further adapter possibly located on the top, guide members 29 in the form of rods or the like intended to establish an adequate mutual location of the adapter and circuit card respectively, which comprise corresponding holes accurately positioned with respect to the conducting pattern on the circuit card. In the embodiment, the guide members 29, which are at least 2 in number, are placed on the movable disk 19. They could of course also be secured to the adapter body 18 and be suitable for projecting through holes in the disk 19 in order to project, at a later point in time, through the holes under discussion in the circuit card. The contact pins 4 are suitably compressible against the action of spring force, more specifically the contact pins comprise a sleeve¬ like body 30, in which the ends 14, 15 of the pins forming rods are received. Within the sleeves 30 there are one or more springs actuating the rods in a direction outwardly from the sleeve to end positions defining the maximum length of the contact pins 4. The test contact spots 3 discussed are here formed by first ends of pin-like contact elements 31. Said first ends are designed on rods 32, which are displaceably received in sleeves 33 of the contact elements 31. The rods 32 are pressable into the sleeves 33 against the action of springs present within the sleeves. Second ends 34 of the contact elements 31 are in contact with other contact elements 35, which in turn are connected, via lower contact parts 36, to a device (not illustrated) generating and receiv¬ ing respectively test signals. The second contact elements 35 are placed in holes provided in a bed or plate 37 belonging to the testing apparatus. The contact elements 35 are, more specifically, arranged in rows and columns in a predetermined, uniform pattern over a substantial contacting area. A disk 38 is placed above the plate 37 and comprises openings so that the ends 34 of the contact elements 31 may pass through into contact with the upper ends of the contact elements 35. The disk 38 is suitably loosely placed above the plate 37. The contact elements 31 are, in the example, included in a second adapter 39 forming an electrically contacting transition from the adapter 1 , more specifically the lower side of its adapter plate 7, to the contact elements 35 of the own bed or plate 37 of the test ap¬ paratus. This further adapter 39 is loosely placeable on top of the bed or plate 37, possibly with the already mentioned disk 38 lo¬ cated therebetween, and does not in principle have to comprise more contact elements 31 than what is corresponding to electrically conducting places 11 on the side 10 of the adapter plate 7. Such a design means that the adapter 39, like the adapter 1 , becomes especially adapted to a certain circuit card design. However, it would also be possible to design the adapter 39 as "complete", i.e. with just as many contact elements 31 as the bed or plate 37 of the test apparatus presents contact elements 35. In such an embodi¬ ment, the adapter 39 could, accordingly, be applied for all occurring circuit card designs. It appears from the above that the contact elements 31 in the adapter 39 extend substantially parallel such that the distribution of the test contact points 3 will match with the distribution of the con- tact elements 35. In this connection it is pointed out that the moti¬ vation proper for the existence of the adapter 39 is based upon a desire for a resilient contact between the electrically conducting places 1 1 on the side 10 of the adapter plate 7 and the contact elements 35 of the bed or plate 37 of the testing apparatus. Such a resiliency gives a more safe and more uniform contacting. In case the own bed or plate 37 of the testing apparatus would be provided with contact elements 35, which would be compressible against the action of spring force and had contact portions intended to get into direct contact with electrically conducting places 11 arranged on the side 10 of the adapter plate 7, the adapter 39 could be avoided entirely. This would, accordingly, mean that the expression "test contact spots" occurring in the enclosed claims should be consid¬ ered as involving not only the contact spots denoted 3 but also contact spots located on the contact elements denoted 35 while avoiding the adapter 39. Expressed in other words, the upper ends of the contact elements 35 could form the test contact spots 3, which is illustrated in Fig 1 by means of the reference character 3a. In the example described, the adapter 39 comprises disks 40 held together mutually, said disks forming, together with occurring spacer members, securing members etc. a rigid body of the adapter 39. The contact elements 31 are received in holes made in these disks 40. It is pointed out only for the sake of clarity that the device as illus¬ trated in Figs 1 and 2 is extremely well suited for use in a state turned upside down or in other orientations; this means that ex¬ pressions indicating direction and used in the above description in no way can be considered to be restrictive as far as the exploitation of the invention is concerned. In a practical circuit card testing case, the following operations are used. Initially, an adapter 1 is produced. The adapter has contact pins 4 placed in adjustment to electrically conducting places which must be tested with regard to their electrical connections to other places on the circuit card. Accordingly, contact pins 4 may occur in a very great number and in a very great density. It may for instance be mentioned that the centre distance between adjacent contact pins 4 may be as small as 0,6 mm or even smaller, whereas an electri¬ cally conducting place on the circuit card may have an extent of 0,3 x 0,3 mm or smaller. The adapter 1 is provided with an adapter plate 7, which on one side 8 thereof is provided with electrically conducting places in correspondence to the electrically conducting places occurring on the circuit card. Thus, the contact pins 4 will function for parallel contacting between the conducting places on the circuit card and the conducting places on the side 8 of the adapter plate 7. The adapter plate 7 is in practice provided with holes disposed in the same disposition as corresponding holes in the circuit card and these holes are plated with electrically conduct¬ ing material on the hole walls proper and also in connection to the holes on the side 8 of the adapter plate 7. On the other hand, there are on the opposite side 10 of the adapter plate 7 between the holes 13 mentioned and the electrically conducting contact places 11 on the adapter plate the previously mentioned conducting paths 12, which are suitable for enabling a spreading of the contacting places 1 1 so that they become distributed in a pattern matching the corresponding pattern with respect to the test contact spots 3 formed by the contact elements 31 or the test contact spots 3a formed directly by the contact elements 35 in the alternative em¬ bodiment which is not illustrated but has been described in princi¬ ple and which does not have an adapter 39. As appears from Fig 3, the holes denoted 13 are provided relatively closely in a group located to the left whereas the conducting paths 12 tend to spread out the contact places 1 1 so that their disposition and mutual dis¬ tance will correspond entirely to corresponding disposition and mutual distance of the test contact spots 3 and 3a respectively. A practical mutual centre distance with respect to the spots 3, 3a may be 2,54 mm. In addition, an adapter 39 is prepared. This adapter may be of a more general nature, i.e. comprise contact elements 31 in corre¬ spondence to the number of contact elements 35 of the bed or plate 37 of the test apparatus but alternatively the adapter 39 may also be specially designed for the circuit card version in question and comprise contact elements 31 in a number and a disposition corresponding to the disposition and number of the contact places 11 on the side 10 of the adapter plate 7. A circuit card to be tested is then placed on the movable disk 19 so that the guide members 29 correspond to corresponding guide members of the circuit card. A suitable pressure pad or alterna¬ tively an overlying adapter is pressed against the circuit card so that the latter and the movable disk 19 are pressed in a direction towards the adapter body 18. The ends 14 of the contact pins 4, which ends are present in the holes 20 in the movable disk 19, will then protrude beyond the disk 19 and enter into contact with elec¬ trically conducting places on the circuit card. At the same time the contact pins 4 will be pressed, with their second ends 15, against the conducting places 9 of the adapter plate 7 and the opposite ends of the contact elements 31 will be pressed against the con¬ ducting places 11 of the adapter plate 7 or the contact elements 35. Test signals are then supplied via the connection parts 36 of the contact elements 35 so that the quality of the occurring conducting paths on the circuit card may be established. It is evident that the device described may be modified in several ways within the scope of the concept of the invention.

Claims: Claims 1. An adapter for use in an apparatus for testing circuit cards, said apparatus comprising a set of test contact spots (3, 3a) in a certain distribution for application of test signals, said adapter comprising contact members (4) adapted to contact electrically conducting places (5) on the circuit card (6) and means for bringing the test contact spots (3, 3a) and contact members into conducting contact with each other, characterized in that the contact means is formed by an adapter plate (7), which on a first side (8) comprises first electrically con¬ ducting places (9) in correspondence to the actual occurrence of contact members (4) and adapted to be contacted by the latter and which on its other side (10) comprises second electrically con- ducting places (1 1 ) having a distribution corresponding to the distri¬ bution of the test contact spots (3, 3a) and intended to contact actual ones of said test contact spots, and that between first and second electrically conducting places (9, 11 ) belonging to each other and being present on the two sides of the plate (7) there are electrical conducting paths (12). 2. An adapter according to claim 1 , characterized in that the electrical conducting paths (12) extend through holes (13) made in the plate (7). 3. An adapter according to claim 1 or 2, characterized in that the contact members (4) are formed by pins intended to contact, by means of first ends (14), conducting places (5) on the circuit card (6) and to contact, by means of second ends (15), the first electrically conducting places (9) on the first side (8) of the adapter plate (7). 4. An adapter according to any preceding claim, characterized in that the contact members (4) are received in aligned holes in disks (16) contained in the adapter. 5. An adapter according to claim 3, characterized in that it comprises a disk (19) movably arranged relative to a body (18) of the adapter, said disk comprising holes (20) for penetration by the first ends of the contact members (4) and being, against the action of spring force, pressable in a di¬ rection towards the adapter body. 6. An adapter according to claim 5, characterized in that it comprises means (21 ) for restricting movements of the movable disk (19) in a direction away from the adapter body (18). 7. An adapter according to claim 6, characterized in that the first ends (14) of the contact members (4) are located substantially flush with or inwardly of the external surface of the movable disk (19) when the disk is spaced from the adapter body. 8. An adapter according to claim 6 or 7, characterized in that said restriction means (21 ) are adjustable for adjustment of the movement end position of the movable disk (19) in a direction away from the adapter body (18). 9. An adapter according to any preceding claim, characterized in that the test contact spots (3) are formed by first ends of pin-like first contact elements (31 ). 10. An adapter according to claim 9, characterized in that second ends (34) of the first contact ele- ments (31 ) are in contact with second contact elements (35), which in turn are connected to a device generating and receiving respectively test signals, said device being contained in the test apparatus.

Inventors: STRANDBERG REINHOLD, STRANDBERG, REINHOLD
Applicants: STRANDBERG REINHOLD, STRANDBERG, REINHOLD
Application year: 1995
Main classification: H05K13
IPC codes: G01R1, H05K13