A SURFACE MOUNT TEST POINT ENABLING HANDS FREE DIAGNOSTIC TESTING OF ELECTRONICAL CIRCUITS

Abstract: The invention relates to a test point enabling hands free diagnostic testing of electronical circuits. The test point according to the invention is characterized in that it comprises a body with two planar, at least essentially parallel end surfaces which are spaced apart and face opposite directions, said end surfaces being connected with each other with a waist portion which is in electrical contact with at least one of the end surfaces.

Description: A Surface Mount Test Point enabling hands free diagnostic testing of electronical circuits The invention relates to a test point enabling hands free diagnostic testing of electronical circuits. Printed circuit boards (PCB) as well as other electronical circuits need to be tested and adjusted. In order to faci¬ litate such testing it is known to use test points which allow the test engineers to work "hands free" while set- ting and adjusting the test equipment. The test points allow the test engineer to attach hook type test probes and log results without having to hold the test probes, used for this purpose. The test points used today for this purpose are in the form of a loop type which is soldered to the PCB with one or two copper pad pieces on the PCB to be tested. Ty¬ pically the loop type test points require a hole through the PCB (which may be plated through) , and there must be at least one pad on the underside of the PCB, which takes board space on the underside of the PCB, which is not re¬ quired with surface mount technology. A pad is required on both the upperside and the underside of the PCB linked with a plated through hole if the signal to be tested is on the upper side of the board. The loop type test point has to be hand-fitted and is often hand-soldered, which makes it expensive and difficult to justify. The object of the present invention is to eliminate the above problems. To achieve this, the test point of the invention is characterized in that it comprises a body with two planar, at least essentially parallel end surfa¬ ces which are spaced apart and face opposite directions, said end surfaces being connected to each other by a waist portion which is in electrical contact with at least one of the end surfaces. The diameter of the waist portion is smaller than the diameter of the end portions: the dia e- ter of the waist portion is chosen to fit in the hooks of common type test probes. The body is preferably symmetri¬ cal and made in one piece of a conducting metal such as brass or copper, the diameter of the end surfaces being somewhat larger than the height of the body. This makes the test point suitable for use in a surface mount device (SMD) machine of standard type. In this case the test points are placed in a surface mount device (SMD) tape of standard type. Preferred embodiments of the test point are disclosed in the attached claims 2 to 12. The present in¬ vention also concerns a surface mount device (SMD) tape provided with test points according to the present inven¬ tion. The most important advantage of the present surface mount test point is that it is very easy to mount on prin¬ ted circuit boards, it is suitable for machine mounting in solder paste which has been applied to the test point pad and can be soldered in a reflow oven. A copper surface of approximately ten square millimeters suffices to function as a mounting base for the test point. The test point can be supplied in a standard 8 mm wide surface mount device tape and can thus be reel mounted. The flat end surfaces of the test point according to the invention allow the test point to be picked up with standard vacuum nozzles. When the diameter of the end portions is larger than the distance between them, the test point is stable and and keeps an upright position, which makes it more reliable to fit. A symmetric test point is preferred, because symmetry makes the test point non handed and subsequently easier to mount in the tape and place on the PCB. In the following the invention will be illustrated by means of one preferred embodiment with reference to the attached drawing, in which Figure 1 shows a commonly used loop-type test point mounted on a printed circuit board and seen from the side, Figure 2 shows the test point of Figure 1 seen from above, Figure 3 shows the test point according to the pre¬ sent invention seen from the side, Figure 4 is a sectional view along the line IV - IV of Figure 3, and Figures 5 and 6 show a surface mount device tape with test points according to Figure 3 placed in the pockets thereof. Figure 1 shows a known loop-type test point. The loop 1 is made of a copper wire having semicircular cross- section so that the ends of the wire are easy to put through the small hole 2 in the printed circuit board (PCB) 3 with the flat sides of the wire facing each other. The hole 2 may be plated through. A copper pad 4 is needed on the underside of the PCB 3, if the signal to be measured with the probe 5 is on the underside of the PCB. If the signal to be measured is on the upperside of the PCB, still another copper pad 6 is needed. The hooks 7 of the probe 5 grip the loop 1. The arrow in Figure 1 shows that the test probe 5 can be attached to the loop through an angle of 180° . Figure 2 shows the loop-type test point seen from above. For the sake of simplicity the test probe 5 has not been illustrated in this figure. The problems with the known loop-type test point have been discussed in the above. Figures 3 and 4 show a surface mount test point according to the present invention. The test point is formed of a body 10 in the shape of a cotton reel. Thus it has two truncated cone portions 20 and 30, each having a planar end surface 40 and 50, respectively. The end surfaces 40, 50 are parallel or almost parallel to each other. Between the cone portions 20, 30 there is a waist portion 60. The test point shown in Figures 3 and 4 is symmetrical to a plane S - S, which is parallel to the end surfaces 40, 50 and which is situated at an equal distance from the end surfaces. The test point 10 is mounted on a copper surface of the PCB 3. A square or round copper pad where the side length/diameter is 3 millimeters is enough to get the test point firmly soldered to the PCB. Even a smaller surface is sufficient for the mounting. The diameter D of the end surface 40 is preferably 2 to 4 mm. The distance L between the end surfaces 40 and 50 is approximately 2 mm. It is preferable that the distance is 0.5 to 0.8 times the diameter D to keep the test point 10 stable and in the correct orientation in the carrier tape and when placed in the solder paste on the PCB. The diameter of the waist portion is approximately 1 mm. As can be seen from Figure 3, the mantle surfaces of the truncated cone portions are at an angle a = ca 20° with respect to the end surfaces 40, 50. The angle a is preferably between 0 and 40° and most preferably between 10 and 30°. When the end portions of the test point have the shape of the cone, the test point possesses better rigidity than if the angle α is very small. A fillet ra¬ dius between the end surfaces and the waisted portion is also permissible. When the test point 10 has the geometry as shown in Figure 3, the probe 5 can be attached to the test point at an angle of 0 to about 30°. The probe 5 can be turned 360° around the test point 10. Figure 4 is a sectional view of the test point ta¬ ken along line IV - IV of Figure 3. As can be seen, the waist portion 60 has a round cross-section. The surface mount test point is made in one piece of solid brass. The test point is preferably plated with tin/gold or some material to maintain its solderable life and prevent oxide buildup. Figures 5 and 6 show a surface mount device (SMD) tape of standard 8 mm wide type in a top view and a side view, respectively, provided with pockets 100 for elect¬ ronical components such as resistors, diodes and capaci¬ tors. Reference numeral 200 designates tape drive holes. In Figures 5 and 6 the pockets have been filled with sur- face mount test points 10 mounted on their end faces so as to present the SMD placement Machine Vacuum nozzle with a flat face according to the invention. The test points ac¬ cording to the invention can be reel mounted to enable them to be SMD machine placeable. The invention has been described above only by way of example, and it is therefore pointed out that the in¬ vention can be modified in many ways within the scope of the claims. Thus, the body 10 need not be symmetrical alt¬ hough this is very desirable; and the end/waisted portions can have any cross sectional shape, eg. a shape of a trun¬ cated pyramid. Instead of brass, the test point can be manufactured of copper or some other metal with good electrical conductivity. In order to save material costs, it is in principle possible to manufacture the test point of any material with sufficient rigidity and durability in temperatures used for soldering, whereby e.g. only the surface is made conductive. In principle, it is sufficient if one end surface is in good electrical contact with the waist portion. This would, however, require correct orien- tation of the test point so that the conducting end surfa¬ ce is against the PCB.

Claims: Claims 1. A test point enabling hands free diagnostic tes¬ ting of electronic circuits, characterized in that it comprises a body with two planar, substan ially pa¬ rallel end surfaces which are spaced apart and face in opposite directions, said end surfaces being con¬ nected to each other by a waist portion which is in olectrical contact with at least one of the end surfaces. 2. A test point according to claim 1, characterized in that the waist portion is in electrical contact with both the end surfaces. 3. A test point according to claim 1 or 2, charac¬ terized in that the body has a shape resembling a cotton reel, whereby at both ends between the waist portion and the end surfaces there is a truncated cone portion. 4. A test point according to claim 3, characterized in that the intersection of end surfaces and the waisted section is a fillet radius. 5. A test point according to claim 3, characterized in that the angle of of the truncated cone portion is between 0 β an d 4 0 " with respect to the end surfaces. 6. A test point according to claim 1 or 2, charac¬ terized in that the body has a shape resembling a cotton reel, whereby at both ends between the waist portion and the end surfaces there is a truncated pyramid portion. 7. A test point according to claim 6, characterized in that the angle of the truncated pyramid portion is between 0° and 40° with respect to the end surfaces. 8. A test point according to any one of the prece¬ ding claims, characterized in that the body is substantially symmetrical with respect to a plane S - S which is parallel to the end surfaces and which is situ¬ ated at an equal distance from the end surfaces. 9. A test point according to any preceding claim, characterize in that the body is made of solid metal in one piece. 10. A test point according to any preceding claim, characterized in that the body is made of brass and is tin-plated. 11. A test point according to any preceding claim characterized in that the end surfaces are equal in diameter D, and that the distance L between the end surfaces is 0.5 to 0.8 times the diameter of the end surfaces. 12. A test point according to claim 11, characterized in that the diameter (D) of the end surfaces is 2 to 4 mm. 13. A surface mount device (SMD) tape for use in a surface mount device (SMD) machine, characterized in that the tape is provided with test points according to any one of the preceding claims. 14. A test point according to any preceding claim, wherein one of said end surfaces is adapted to be attached to a printed circuit board track by an electrically conductive material. 15. A test point according to any preceding claim, wherein said waist portion is adapted to receive a test probe with a loop or hooks, said waist portion thus retaining said test probe, enabling hands free testing of printed circuit boards. 16. A test point substantially as hereinbefore described, with reference to Figs 3 to 6 of the accompanying drawings. 17. A surface mount device (SMD) tape for use in a surface mount device (SMD) machine, substantially as hereinbefore described, with reference to Figs 3 to 6 of the accompanying drawings. AMENDED CLAIMS [received by the International Bureau on 5 March 1996 (05.03.1996); original claims 16 and 17 cancelled; remaining claims unchanged (2 pages)] 1. A test point enabling hands free diagnostic testing cf electronic circuits, c a r a c t e r i z¬ e d in that it comprises a body with two planar, sub¬ stantially parallel end surfaces which are spaced apart and face in opposite directions, said end surfaces being connected tc each other by a waist portion which is in electrical contact with at least one of the end sur¬ faces. 2. A test point according to claim 1, c h a r¬ a c t e r i z e d in that the waist portion is in electrical contact with both the end surfaces. 3. A test point according to claim 1 or 2, c h a r a c t e r i z e d in that the body has a shape resembling a cotton reel, whereby at both ends between the waist portion and the end surfaces there is a trun¬ cated cone portion. .5. A test point according to claim 3, c h a r¬ a c t e i z e in that the intersection of end sur¬ faces and the waisted section is a fillet radius. 5. A test poir;t according to claim 3, c h a r¬ a c t e r i z e d in that the angle α of the truncated cone portion is between 0 C and 40° with respect to the end surfaces. β. A test point according to claim 1 or 2, c h a r a c t e r i z e d in that the body has a shape resembling s cotton reel, whereby at both ends between the waist portion and the end surfaces there is a trun¬ cated pyramid portion. 7. A test point according to claim 6, c a r¬ a c e r i z e d in that the angle of the truncated pyramid portion is between 0° and 40° with respect to the end surfaces. AMENDED SHEET (ARICL119) 8. A test point according to any one of the preceding claims, c h a r a c t e r i z e d in that the body is substantially symmetrical with respect to a plane S - £ which is parallel to the end surfaces and which is situated at an equal distance from the end surfaces. 9. A test point according to any preceding claim, c h a r a c t e r i z e d in that the body is made of solid m l in one piece. 10. A test point according to any preceding claim, c h a r a c t e r i z e d in that the body is made of brass and i3 tin-plated. 11. A test point according to any preceding claim, c h a r a c t e r i z e d in that the end sur- faces are equal in diameter D, and that the distance between the end surfaces is 0.5 to O.ε times the diame¬ ter of the end surfaces. 12. A test point according to claim 11, c h a r a c t e r i z e d in that the diameter {D) of the end surfaces is 2 to 4 mm. 13. A surface mount device (SMD) tape for use in a surface mount device (SMD) machine, c h a r a ¬ t e r i z e d in that the tape is provided with test points according to any one of the preceding claims. 14. A test point according to any preceding claim, wherein one of said end surfaces is adapted to be attached to a printed circuit board track by an elec¬ trically conductive material. 15. A test point according to any preceding claim, wherein said waist portion is adapted to receive a test probe with a loop or hooks, said waist portion thus retaining said test probe, enabling hands free testing of printed circuit boards. EET ICLE 19.

Inventors: TALBOT ANDREW, TALBOT, ANDREW
Applicants: NOKIA TELECOMMUNICATIONS OY, TALBOT ANDREW, TALBOT, ANDREW
Application year: 1995
Main classification: G01R31
IPC codes: G01R1, G01R31, H01R12, H05K3