Abstract:
A test point enabling hands-free diagnostic testing of electronical circuits, has a body with two planar, at least substantially parallel end surfaces which are spaced apart and face opposite directions. The end surfaces are connected with each other by a waist portion which is in electrical contact with at least one of the end surfaces.

Description:
This application claims benefit of international application PCT/FI 95/00497, filed Sep. 13, 1995. 
    
    
     This application claims benefit of international application PCT/FI 95/00497, filed Sep. 13, 1995. 
     BACKGROUND OF THE INVENTION 
     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 facilitate such testing it is known to use test points which allow the test engineers to work &#34;hands free&#34; while setting 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 which is soldered to the PCB with one or two copper pad pieces on the PCB to be tested. Typically, 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 required 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. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to eliminate the above problems. To achieve this, the test point of the invention it comprises a body with two planar, at least essentially parallel end surfaces which are spaced apart and face opposite directions, the 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 diameter of the waist portion is chosen to fit in the hooks of common type test probes. The body is preferably symmetrical 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. The present invention also concerns a surface mount device (SMD) tape provided with test points according to the present invention. 
     The most important advantage of the present surface mount test point are that it is very easy to mount on printed 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 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be illustrated by means of one preferred embodiment with reference to the attached drawing, in which: 
     FIG. 1 shows a commonly used loop-type test point mounted on a printed circuit board and seen from the side, 
     FIG. 2 shows the test point of FIG. 1 seen from above, 
     FIG. 3 shows the test point according to the present invention seen from the side, 
     FIG. 4 is a sectional view along the line IV--IV of FIG. 3, and 
     FIGS. 5 and 6 show a surface mount device tape with test points according to FIG. 3 placed in the pockets thereof. 
    
    
     DETAILED DESCRIPTION 
     FIG. 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 FIG. 1 shows that the test probe 5 can be attached to the loop through an angle of 180°. 
     FIG. 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. 
     FIGS. 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 (i.e, in the shape of a spool for sewing thread) having an axially central spindle terminating in two opposite end flanges which are larger in diameter than the spindle. 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 FIGS. 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 L be 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 FIG. 3, the mantle surfaces of the truncated cone portions are at an angle α=about 20° with respect to the end surfaces 40, 50. The angleα 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 a is very small. A fillet radius between the end surfaces and the waisted portion is also permissible. When the test point 10 has the geometry as shown in FIG. 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. 
     FIG. 4 is a sectional view of the test point taken along line IV--IV of FIG. 3. As can be seen, the waist portion 60 has a round transverse 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. 
     FIGS. 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 electronical components such as resistors, diodes and capacitors. Reference numeral 200 designates tape drive holes. In FIGS. 5 and 6, the pockets have been filled with surface 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 according 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 invention can be modified in many ways within the scope of the claims. Thus, the body 10 need not be symmetrical although this is very desirable; and the end/waisted portions can have any cross sectional shape, e.g. a shape of a truncated 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 orientation of the test point so that the conducting end surface is against the PCB.