DE102005042521A1 - Method and apparatus for a twisting mount probe for probing test access point structures - Google Patents

Abstract

A twisting mount probe for cleaning oxides, residues or other contaminants from the surface of a solder bead probe and probing a solder bead probe on a printed circuit board during in-circuit testing.

Description

Of the The subject of this patent application is the same of the US patent application Ser. No. 10 / 670,649, entitled Printed Circuit Board Test Access Point Structures and method for making the same, filed on September 24, 2003 by Kenneth P. Parker, Ronald J. Peiffer and Glen E. Leinbach and transferred to Agilent Technologies, Inc., which is hereby incorporated herein by reference. The subject of this patent application is further with the same of the US patent application entitled Method and apparatus for manufacturing and probing Printed Circuit Board Test Access Point Structures (Method And Apparatus For Manufacturing And Probing Printed Circuit Board Test Access Point Structures), filed October 25, 2004 by Kenneth P. Parker and Chris R. Jacobsen and transferred to Agilent Technologies, Inc., which is hereby incorporated herein by reference.

printed Circuitry (PCAs = Printed circuit assemblies) are typically tested after manufacture to ensure the continuity of printed conductors between connection surfaces and vias on the board to verify and to verify that components that are populated on the board behave within specifications. Such printed circuit arrangement testing is generally used with automated in-circuit testers or In-circuit testers or ICTs performed and requires complex Tester resources. The tester hardware must generally be used for probing or investigate more conductive Pads Vias and traces on the test board in the To be able to do.

Internal circuit Testers (ICT) used conventionally a "bed of nails" access (BON access; BON = "bed-of-nails") to an electric connectivity with a circuit wiring (tracks, networks, pads) for one at a Testing needed Control and observation capability to win. The Agilent 3070 is a typical in-circuit tester and is owned by Agilent Technologies, Inc. of Palo Alto, California, available. This requires access points within the layout of circuit networks to show the goals for ICT probes could be. Test access points are usually circular targets with 711.2 to 889 μm (28 up to 35 thousandths of an inch) diameter, with traces at the printed circuit board are connected. In some cases these goals intentionally added Testpads and in other cases The goals are "via" pads, which are already printed in the Circuit surrounding existing vias.

It is increasingly difficult, targets with smaller diameter reliable and repeatable, especially if a test fixture may be contains several thousand of such probes. It is always desirable goals with a larger diameter to use, but this is in a fundamental conflict with the industrial trend to higher densities and devices with smaller geometry.

Yet another industry trend is having always, logic families higher Speed to use. One-megahertz (MHz) designs were made to ten-MHz designs, then to 100 MHz designs and now reach the gigahertz range. The Increases in logic speed are paying attention the industry for Board layout rules for Connections with higher Speed required. The purpose of these rules is to to create a controlled impedance path that produces noise, a crosstalk and minimize signal reflections. Printed circuit board traces, The high-speed signals tend to have critical layout requirements and require controlled characteristic impedances. If conventional Added test probe targets this will cause discontinuities in the controlled impedances and can damage signal accuracy.

1A provides a classic pair of differential transmit signal traces 102 . 102b at a portion of a printed circuit board 100 As shown, the printed circuit board is 100 formed as a plurality of layers. In the illustrative embodiment, the printed circuit board includes 100 a ground plane 104 that have a substrate 105 layered, a dielectric 103 that is above the ground plane 104 is layered, tracks 102 . 102b passing over the dielectric 103 layered, and a solder mask 106 that go over the tracks 102 . 102b and exposed surfaces of the dielectric 103 is layered. In such a layout, there are a number of critical parameters that affect the impedance of the signal path. These parameters include a trace width 110 , a track separation 111 , a trace thickness 112 and dielectric constants of the solder mask and the board material. These parameters affect the inductance, capacitance and resistance (skin effect and DC) of the tracks, which combine to determine the transmission impedance. It is generally desirable to have this value throughout the entire run of each trace 102 . 102b to control.

at some designs with higher Speed, it is also important to the symmetry of the tracks to control. Leading (Routing) of signals on a heavily populated printed circuit board however, requires curves and bends in the path, whatever lengths and lengths Makes symmetries more difficult. In some cases, series components (such as for example, row terminations or DC blocking capacitors) in the path Its and these have dimensions that differ from the layout parameters differ. Signals have to furthermore possibly cross connectors, which increases the difficulties.

One Another trend is for boards with ever higher density, which also layout critical are. If conventional Test probe targets are added to a high density board, the board layout is generally disturbed, with an addition of Test probe targets to one or more nodes moving out of the way required by several others. Such changes high-density boards may not be practical in many cases, because there may be no room to move tracks. If any of the signal traces further randomly carry high frequency signal traces are, then you can the bends that needed to redirect them also have a negative performance effect and the negative effects of the conventional target itself.

Additional difficulties arise when testing is considered. Testing requires tester access to circuit traces at particular probe targets. Layout rules typically require test targets to be at least 1270 μm (50 mils) apart and may require that the diameter of the test point targets greatly exceed the width of the traces. 1A and 1B make test targets 115a . 115b symmetrically 1270 μm (50 mils) apart on the differential signal traces 102 . 102b are positioned. As it is in 1A and 1B can be seen, will be great test objectives 115a through a typical mounting probe 116 with a sharp head 120 probes such as those available from Interconnect Devices, Inc., 5101 Richland Avenue, Kansas City, KS 66106. The sharp probes 116 help break any oxide or residue that is at the test targets 115a and 115b is constructed.

The positioning of test targets 102 . 102b can be problematic. In many cases, the need to maintain a minimum separation between targets (typically 12 mils (50 mils), minimum) directly conflicts with the layout rules of a controlled impedance. These conflicts either result in a compromise in controlled impedance integrity and optimal circuit layout for performance and space, or forced reduction in target placement with a resulting reduction in testability.

While printed High speed circuit boards an example of layout critical circuits Another common case is that of high-end boards Density. An addition of conventional Probe targets to a high density board are very likely to interfere with this Layout. For example, adding test points makes only One or more nodes move one out of the way other tracks required. In many cases, this may be the case in a circuit design high-density impractical if not impossible, as it may There is no room for these tracks in a heavily populated circuit layout to move. If any tracks further comprise high frequency signal traces then redirecting can have an additional negative performance effect as well as the negative effects on the optimal circuit layout own.

As more fully described in US patent application Ser. No. 10 / 670,649, entitled Printed Circuit Board Test Access Point Structures and Method of Making the same, filed Sep. 24, 2003 by Kenneth P. Parker et al. And the U.S. patent application entitled Method and Apparatus for Making and Probing Printed Circuit Boards. Test Methods Point (Method And Apparatus For Manufacturing And Probing Printed Circuit Boards Test Access Point Structures), filed October 25, 2004 by Kenneth P. Parker and discussed in US Pat 2A - 2C A new example has been developed to replace the old test example in which large test targets were laid out on a printed circuit board and probed with sharp probe mounting probes mounted in a test fixture.

As it is in 2A - 2C shown are small semi-elliptical solder beads or test access points 18a and 18b by exploiting the z-dimension to the tracks 12a and 12b on a printed circuit board 10 added without disturbing the layout of the board or performance. As illustrated, the printed circuit board is 10 formed as a plurality of layers. In the illustrative embodiment, the printed circuit board includes 10 a ground plane 14 that have a substrate 15 layered, a dielectric 13 , above the ground plane 14 is layered, tracks 12a . 12b that over the dielectric 13 are layered, a solder mask 16 that over exposed surfaces of the tracks 12a and 12b and the dielectric 13 is layered, and test access points 18a and 18b ,

As noted above, an important factor in probing is obtaining good electrical contact between the fixture probe and the test target. In the old example, this was typically done by probing with a sharp probe tip 120 handled. However, this method can be used with bead probes or test access point structures 18a and 18b Since the test access point structures may have very small dimensions in the xy plane, on the order of 76.2 - 127 μm (3 - 5 mils) wide by 381 - 508 μm (15 - 20 mils) long or less , Current designs for test guidelines for ICT (in-circuit testers) require a test interface or target of at least 762 μm (30 mils) diameter by a chisel or spearhead probe. The small dimensions of the test access point structures in the xy plane in combination with the small dimensions of the chisel or spearhead test fixture probe would most likely create test access accuracy and reliability issues. It can simply be difficult to hit a small target with a sharp tip probe with current industry test fixture standards. Further, while a chisel or spearhead test fixture probe may be effective in perturbing surface contaminants at a 762 μm (30 mils) or more test pad, assuming it has a test access point structure of 76.2 - 127 μm (3 - 5 mils) could most likely severely damage the test access point structure. There is a need in the industry for a method to ensure good electrical contact between bead probes or test access point structures and mounting probes.

It It is the object of the present invention to provide a method for implementing a twisting mount probe, a method of probing a solder bead probe on a printed circuit board, a mounting probe and a method for cleaning a solder bead probe on a printed circuit board with improved characteristics create.

These The object is achieved by a method according to claim 1, claim 7 and Claim 20 and a mounting probe according to claim 13 solved.

The present invention solves the problem, such as good electrical contact between a solder bead probe or a test access point structure and a mounting probe for a printed circuit board testing to obtain is.

at an embodiment can be a surface a solder bead probe by a rotational movement of a twisting mounting probe be cleaned when the twisting mounting probe in a Compression contact with the solder bead probe is brought.

at an exemplary method for implementing the twisting Mounting probe becomes a substantially flat tip on one Rotary member mounted, which is in operative contact with a rotating mechanism and a spring force is brought and connected to the same.

at an exemplary method for cleaning and probing a Solder bead probe on a printed circuit board becomes a twisting mount probe with a solder bead probe aligned and in a compression wiping contact with the same brought. Testing can then be performed, with the Bracket probe in contact with the solder bead probe.

One complete understanding of this invention and many of the attendant advantages thereof readily apparent when the same by reference to the following detailed description considered in connection with the associated Draws more apparent in which like reference numerals the same or similar Specify components.

preferred embodiments The present invention will be described below with reference to FIG the enclosed drawings closer explained. Show it:

1A Figure 12 is a plan view of a conventional printed circuit board with traces showing the x and y dimensions in the x, y, z coordinate system;

1B Fig. 12 is a cross-sectional side view of the printed circuit board with differential signal traces showing the x and z dimensions in the x, y, z coordinate system;

2A Fig. 12 is a plan view of a printed circuit board showing the x and y dimensions of the differential signal traces in the x, y, z coordinate system with a test access point structure;

2 B FIG. 16 is a cross-sectional side view of the printed circuit board in FIG 2A showing the z and x dimensions in the x, y, z coordinate system with a test access point structure;

2C FIG. 16 is a cross-sectional side view of the printed circuit board in FIG 2A showing the z and y dimensions in the x, y, z coordinate system with a test access point structure;

3 Fig. 12 is a cross-sectional side view showing a portion of a printed circuit board having a test access point structure on a trace and a mounting probe contacting the test access point structure;

4A Fig. 12 is a cross-sectional side view showing a portion of a printed circuit board having a test access point structure on a trace and a twisting mount probe contacting the test access point structure according to the invention;

4B Figure 11 is a plan view of a test access point structure with one of the same imposed twisting support probes according to the invention;

5 a side perspective view of a test access point structure with a twisting mounting probe according to the invention;

6 an operational flowchart illustrating a method of implementing a twisting mount probe according to the invention; and

7 10 is an operational flow diagram illustrating a method of testing a test flow point structure on a printed circuit board trace with a twisting mount probe according to the invention.

Under Now, detailed reference to the invention will be apparent to those skilled in the art in the field, that on a trace, in an x, y, z coordinate system is defined, where the x-dimension represents the track width, the y dimension the trace length represents and the z-dimension represents the trace thickness, present techniques for a test access point placement on a printed circuit board, only the x and the Use y dimension. The present invention takes advantage of exploiting the z dimension, d. H. the conductor track thickness, a different approach. In this The test access point structure of the invention is a localized high Point "at one Printed circuit board trace, showing the impedance of the trace does not bother significantly and which can be targeted with a probe. Everywhere in this description Both test access point structure and bead probe structure become interchangeable used.

As more fully discussed in the above-referenced patent applications 3 one possible method to ensure electrical contact between the mounting probe and the test access point structure. 3 FIG. 12 illustrates a side cross-sectional view of a mounting probe contacting a test access point structure according to the invention. FIG. As it is in 3 has a printed circuit board 10 a substrate 15 , a ground plane 14 and at least one dielectric layer 13 with at least one track 12 which is printed, applied or otherwise attached to the same. A solder mask 16 with a hole over the track 12 is formed at a position where a test access point structure 18 is over the exposed surfaces of the dielectric layer 13 and the wiring layer 12 positioned. The test access point structure 18 becomes conductive at the track 12 inside the solder mask hole 17 attached to the test access point. The test access point structure 18 stands over the exposed surrounding surfaces of the solder mask 16 to an exposed, localized, high point on the track 12 during testing of the printed circuit board 10 through a mounting probe 35 can be electrically touched or contacted as a test target.

As discussed above and in 3 is shown when the mounting probe 35 in an initial compression contact with the test access point structure 18 is brought, deforms the test access point structure and forms a substantially flat top surface 32 which moves any surface oxide, residues or contaminants and good electrical contact between the mounting probe 35 and the test access point structure 18 allowed. The compressive force between the mounting probe and the test access point structure 18 may be any known device, such as a spring-loaded mount probe 35 with a shaft 36 , a spring mechanism 37 and a substantially flat contact area 38 ,

For purposes of discussion, assume that the mounting probe has a flat surface with the test access point or bead 18 comes into contact. If the radius of curvature is tight enough, the test access point structure is subject 18 made of solder, a deformation when a mounting probe touches the same with a predetermined amount of force. A typical mount probe force is approximately 113.4 - 226.8 g (4 - 8 ounces). The yield strength of typical solders (both leaded and lead-free) carries approximately 344.7 bar (5000 psi). Thus, if a mounting probe has a newly formed bead or test access point 18 Touching for the first time compresses the test access point 18 with a substantially flattened upper end. The flat area 32 grows when the solder deforms until the flat area 32 is large enough to carry the mount probe force. The process of deforming the bead or test access point 18 displaces any surface oxides, contaminants or residues and gives the mount probe excellent electrical contact with the test access point solder 18 ,

Analogous You can get a potato as a bead probe and the potato skin as surface contaminants, Imagine radicals or oxides. The potato is on a flat hard surface placed. A second object representing a mounting probe and a flat, hard surface having a diameter at least as large as the same The potato is in compression contact with the potato brought up the surface the potato starts to deform and flatten. If this happens, the potato skin is deformed and the flat surface of the second object, which represents the mounting probe, comes into contact with the inside of the potato containing a non-contaminated solder represents the bead probe.

As an exemplary model, the yield strength of the solder is approximately 344.7 bar (5000 psi) or 2.268 g per 0.0006452 mm ² (0.005 pounds per thousandth of a square inch) or 2268 mg per 0.0006452 mm ² (0.08 ounces per thousandth of a square inch). Thus, to carry a typical flat-bottomed 113.4 g (4 ounce) probe, the flattened area must 32 the test access point 18 0.03226 mm ² (4 / 0.08 or 50 thousandths of a square inch). Take a 127 μm (5 mils) wide by 508 μm (20 mils) long ridge 18 which is approximately 76.2 μm (3 mils) high. Suppose that if the bracket probe the bead 18 first touched, there is no flattened surface area. Then, when the retainer probe presses down on the solder, the area that is flattened approaches 32 to an ellipse with a width-to-length ratio of 1: 4. As this area increases, the solder elongation begins to slow until there is a "footprint" of 0.03226 mm ² (50 mils) or approximately 1/2 of the total area of the bead itself, once the surface area is large enough In order to support the mount probe force, no further deformation occurs, and subsequent probing does not produce any further deformation.

Once probing has flattened a bead probe, the solder bead is subject to the growth of a new layer of oxide coating or other surface contaminants as time passes. Therefore, if the board is returned from the site for retesting or if the board would have to undergo a repair and re-test cycle, it may become a new oxide or contaminant layer on the surface of the bead probe 18 give. Since the flattened head is already capable of supporting the probe force, no new deformation should occur to displace this oxide or contaminant layer. While a lead-free solder (containing mostly tin) may grow a conductive tin oxide layer, an older leaded solder may eventually grow into a lead oxide layer, which is a poor conductor. Thus, this oxide layer or other surface contaminants may adversely affect re-testing.

This problem can be addressed by using a smooth-surfaced probe which rotates or twists about its long axis (about the z-axis). 4A provides a twisting mount probe 40 in contact with a bead probe or a test access point structure 18 on a printed circuit board 10 according to the invention. When the twisting probe 40 inside the drawn drum thereof, an internal flange or other known mechanism causes it to rotate about the z-axis a predetermined number of degrees. This causes the twisting mount probe 40 when it rotates the bead probe 18 which causes a wiping action which causes the bead probe surface 32 cleanly polished from any oxide, residue or contaminant buildup. The twisting mounting probe 40 can be a bit 44 with a relatively flat or smooth surface because, on a microscopic scale, this is actually a rough surface containing the oxide, remainder or contaminants from the bead probe surface 32 Abschleift, with a reasonable electrical contact between the bead probe 18 and the twisting mount probe 40 is restored.

4B Fig. 10 is a plan view of the bead probe 18 wherein a probe tip 44 the same is superimposed, wherein the rotary action is shown when the mounting probe 40 in compression contact with the bead probe 18 is brought. 4B is with some misalignment between the bead probe 18 and the mounting probe tip 210 showing the same for a bead probe 18 of approximately 76.2 - 127 μm (3 - 5 mils) by approximately 381 - 508 μm (15 - 20 mils) and a mounting probe tip 210 with a diameter of approximately 584.2 - 889 μm (23 - 35 tau sendstel inch) picks up some system misalignment.

5 illustrates an exemplary embodiment of the twisting mount probe 40 which is a cylindrical member 41 having a shank 42 häust, at a relatively flat top 44 is appropriate. The shaft 42 causes the tip 44 rotates about the z-axis when the same by a force, such as a spring force 43 into compression contact with the bead probe 18 is brought. The shaft 42 may be a relatively square shaft that has been twisted about the long axis thereof, such as a twisted licorice stick. If the twisted square shaft 42 by the spring force 43 it can be in contact with a flange or recess 45 in the wall of the cylindrical member 41 reach, causing the shaft 42 and the top 44 rotate. There are other expected facilities to make that the top 44 rotates by a predetermined amount when the tip 44 in compression contact with the bead probe 18 is brought, the surface 42 the bead probe 18 is effectively cleaned.

6 is an operational flowchart 50 for a method of implementing a twisting mount probe according to the invention, wherein in one step 52 a building song 44 with a relatively flat tip on a rotary member 42 is attached, such as a rotating shaft. The rotary member 42 becomes at one step 54 brought into operative contact with a rotating mechanism, such as a flange or a recess 45 , The rotary member becomes at one step 56 in operative contact with a compression mechanism 43 brought, such as a spring force. The rotating mechanism may be another known device, such as a substantially square hole at the end of the cylindrical member 41 closest to the top 44 such that the twisted shaft member 42 turns when the pressure force 43 the twisted shaft member 42 is forced through the substantially square hole, causing the tip 44 rotates by a predetermined amount of rotation.

7 is an operational flowchart for a process 60 for probing a bead probe with a twisting mount probe according to the invention. In operation, a twisting mounting probe 40 in a test fixture with a test access point structure 18 on a conductor track 12 a printed circuit board 10 at one step 62 aligned. At one step 64 becomes a substantially flat top 44 the twisting mounting probe 40 in contact with an upper surface of a test access point structure 18 brought. At one step 66 An electrical contact is ensured when the upper surface 32 the test access point structure 18 is cleaned of any oxides, residues or contaminants when the substantially flat tip 44 by applying a compressive force 43 to a rotary member 42 is turned. After electrical contact is ensured, tests may be performed that provide electrical contact between the test access point structure 18 and mounting probe 40 require.

Out the above detailed description of the invention is evident that the present invention clearly solves the conflict problems that by conventional Techniques for a test access point placement on printed circuit boards be encountered. Although this preferred embodiment of the present invention for for illustrative purposes is one of skill in the art It can be seen that various modifications, additions and Substitutions are possible, without departing from the scope and spirit of the invention, as it is in the associated claims is defined. For example, you can the test access targets by some means other than be deformed by contact with the mounting probes. Further can Bead probes printed on one or both sides of a two-sided Circuit board to be implemented. It is also possible that Other advantages or uses of the presently disclosed invention become obvious over time.

Claims (20)

Method for implementing a twisting mount probe ( 40 ), the method comprising the steps of: attaching (step 52 ) of a substantially flat tip ( 44 ) on a rotary member ( 42 ); Attach (step 54 ) of the rotary member ( 42 ) into operative contact with a rotating mechanism ( 41 and 45 ); and attaching (step 56 ) of the rotary member ( 42 ) into operative contact with a compressive force ( 43 ). Method according to Claim 1, in which the substantially flat tip ( 44 ) is a substantially circular, flat tip. Method according to claim 2, wherein the substantially circular, flat tip ( 44 ) has a diameter of approximately 584.2 - 889 μm (23 - 35 thousandths of an inch). Method according to one of claims 1 to 3, wherein the rotary member ( 42 ) a twisted having a square shaft. Method according to claim 4, wherein the rotating mechanism is a flange ( 45 ) in a cylindrical housing ( 41 ), which is the twisted square shaft ( 42 ) surrounds. Method according to Claim 5, in which the pressure force ( 43 ) is a spring force at a first end of the twisted square shaft opposite a second end of the twisted square shaft on which the substantially circular, flat tip ( 44 ) is attached. A method of probing a solder bead probe on a printed circuit board, the method comprising the steps of: aligning (step 62 ) a twisting mounting probe ( 40 ) with a solder bead probe ( 18 ), which are conductive to a conductor track ( 12 ) on a printed circuit board ( 10 ) is attached; bring in contact (step 64 ) a tip ( 44 ) of the twisting mounting probe ( 40 ) with the solder bead probe ( 18 ); and rotate (step 66 ) the top ( 44 ) of the twisting mount probe when the tip ( 44 ) in compression contact with the solder bead probe ( 18 ) is brought. The method of claim 7, further comprising the step of performing (step 68 ) of one or more tests, wherein the rotating support probe is in compression contact with the solder bead probe. Method according to claim 7 or 8, wherein the tip ( 44 ) of the twisting mounting probe ( 40 ) is substantially flat. Method according to claim 9, wherein the tip ( 44 ) of the twisting mounting probe ( 40 ) is substantially flat on the surface that contacts the solder bead. Method according to claim 10, wherein the tip ( 44 ) of the substantially flat, twisting mounting probe ( 40 ) is substantially circular. The method of claim 11, wherein the diameter of the substantially circular tip 44 the substantially flat, twisting mounting probe ( 40 ) is approximately 584.2 - 889 μm (23 - 35 thousandths of an inch). Holding probe, comprising: a substantially flat tip ( 44 ); a rotary member ( 42 ), which is at the substantially flat top 44 is appropriate; a rotating mechanism ( 41 and 45 ) attached to the rotary member ( 42 ) is attached; and a compression mechanism ( 43 ). A mounting probe according to claim 13, wherein the substantially flat tip ( 44 ) is substantially flat in the xy plane of the x, y, z coordinate system. A mounting probe according to claim 14, wherein the substantially flat tip ( 44 ) is substantially circular with a diameter of approximately 584.2 - 889 μm (23 - 35 thousandths of an inch). Holding probe according to one of claims 13 to 15, wherein the compression mechanism ( 43 ) is a spring force. A mounting probe according to any one of claims 13 to 16, wherein the rotary member ( 42 ) is a substantially square, twisted shaft. A mounting probe according to claim 17, wherein the Rotary mechanism a flange in a housing around the substantially square, twisted shaft is around. A mounting probe according to claim 17, wherein the Rotary mechanism a recess in a housing around the substantially square, twisted shaft is around. A method of cleaning a solder bead probe on a printed circuit board, the method comprising the steps of: contacting (step 64 ) a mounting probe ( 40 ) with a substantially flat tip ( 44 ) with the bead probe 18 ; and twisting (step 66 ) of the flat tip ( 44 ) of the mounting probe ( 40 ), when the mounting probe is in compression contact with the solder bead probe ( 18 ) is held.