Probe for use in determining an attribute of a coating on a substrate

A probe provides electrical communication between a coating and a processing system. One optional feature includes an outwardly projecting, electrically conductive engaging member that is held in a captivation structure releasably retained in a housing and engages a contact that is inside the probe and connected with the processing system. Another optional feature of the probe provides the electrically conductive engaging member in the form of a pin or pins captivated in a light-transmissive structure adjacent a light-emitting source. Another optional feature of the probe includes a restraining structure that defines a frustoconical seat for engaging a conical distal end of an electrically conductive pin that is adapted to contact the coating.

CROSS REFERENCE TO RELATED APPLICATION(S)

REFERENCE TO A MICROFICHE APPENDIX

TECHNICAL FIELD

This invention relates to a probe for providing electrical communication between a material (e.g., a coating defined by a film or layer on a substrate) and a processing system (e.g., analyzing system) that determines an attribute of the material (e.g., the thickness of a coating) by analysis of detected or sensed phenomena in the material (e.g., an electrical characteristic temporarily established in the material as a result of the application of electrical energy to the probe near, or in contact with, the material).

BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART

Some attributes (i.e., characteristics or features) of a material can be determined (e.g., measured) with an appropriate instrument. For example, various models of instruments for non-destructively measuring the thickness of a film or layer (i.e., coating) of copper as electroplated on a printed circuit board are sold by Oxford Instruments Coating Measurement, a part of the Oxford Instruments Analytical division of Oxford Instruments plc (hereinafter referred to as “Oxford”), which has a place of business at 945 Busse Road, Elk Grove Village, Ill. 60007, U.S.A. Typically, during the manufacture of a printed circuit board, it is desirable to know whether or not the design specifications are being met by, inter alia, the copper coating(s) on a substrate component of the printed circuit board. In particular, it typically is important to know the thickness of the copper coating(s) within some sufficient range of precision and accuracy in order for the manufacturer to determine whether or not the copper thickness on a portion or portions of the printed circuit board is within the allowable manufacturing tolerances as established by the design.

Different systems can be employed in an instrument to measure a feature, such as a coating thickness. These systems can include, for example, the use of a probe employing magnetic induction, eddy currents, or micro-resistance methods or techniques. Selection of the technique to be employed can depend on various factors (e.g., the type of coating material, geometric configuration of the coating and substrate, desired accuracy and precision, size of the area being measured, range of thickness to be measured, efficiency of use, ambient environmental conditions, and cost). Such a probe may employ one or more contact members for engaging the coating, and the probe may be a separate, hand-held probe, or may be mounted in a stationary device.

Although Oxford markets probes that are designed for various applications and that function exceptionally well in systems efficiently performing measurement analyses (such as measurement of a coating thickness), it would be desirable to provide improved probe features that would result in, or accommodate, even better performance, greater functionality, more versatility, ease of use, ease of manufacturing, lower cost manufacture, and/or improvement in accuracy, precision, efficiency of use, tolerance of ambient environmental conditions, and durability.

It would be particularly advantageous to provide an improved probe that optionally could be selectively configured with a different tip geometry to maximize accuracy and precision in various applications and/or that optionally could accommodate replacement of a worn or broken component.

It would also be beneficial to provide an improved probe permitting the user or operator to better observe the end of the probe and the adjacent portion of the material where the particular attribute of the material (e.g., thickness) is to be determined by the use of the probe.

Also, with a probe of the type that employs a pin or pins for engaging or contacting a material (e.g., a copper coating), it would be desirable to provide an improved probe that has greater pin stability so as to minimize deleterious effects on measurement precision.

The present invention provides an improved probe which can accommodate designs having one or more of the above-discussed benefits and features.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the present invention can be incorporated in a portable or stationary probe that may include one or more of the above-discussed, desired features. According to a first aspect of the present invention, a probe provides electrical communication between a coating on a substrate and a processing system that determines an attribute of the coating (e.g., such as the thickness of the coating) by detection of phenomena resulting from the application of electrical energy to the probe in contact with the coating. The probe has one or more engaging members which can engage the coating and which can be readily removed by the user to allow replacement by the user if the electrically conducting engaging members become worn or damaged, or if it is desired to use new electrically conducting engaging members arranged in a different configuration and/or having different characteristics.

In particular, in the presently preferred embodiment which incorporates the first aspect of the invention, the probe comprises a housing and at least one contact mounted within the housing. The probe further includes an electrical circuit adapted to provide electrical communication between the contact and the processing system (which may be remote from the probe). The probe also includes at least one electrically conductive engaging member that (1) has a distal end projecting outwardly for engaging the coating, (2) has a proximal portion in the housing for engaging the contact and for accommodating disengagement from the contact, and (3) is captivated partially in an electrically insulating captivation structure which can be manually grasped by a user for removal from the housing together with the captivated electrically conductive engaging member.

In accordance with this first aspect of the invention, the presently preferred form of the electrically conductive engaging member is a pin which defines the distal end of the engaging member projecting outwardly for engaging the coating and which defines the proximal portion of the engaging member for engaging the contact. According to the first aspect of the invention, the presently preferred form of the probe captivation structure is molded or machined from a thermoplastic material having a hole or passage in which a portion of the pin is captivated to hold the pin in a fixed orientation. The pin and the captivation structure together define an integral unit in the form of a nose assembly which may be characterized as a probe tip that has (1) an inner portion that is releasably received in the housing, and (2) an extending portion that (a) projects from the housing, and (b) can be manually grasped by a user for pulling the tip out of the housing without using a tool.

Further, in the presently preferred form of a probe incorporating the first aspect of the invention, the housing is a hand-held or hand-holdable, tubular structure defining a receiving cavity with an access opening for accommodating insertion of the probe tip. Each contact is mounted in the receiving cavity of the housing and includes an arm that is elastically deflectable in response to a force exerted by the proximal portion of a pin which engages the contact arm.

In the presently preferred form of a probe incorporating the first aspect of the invention, a snap-fit engagement releasably retains the probe tip in the housing. To that end, the tubular structure of the housing has a peripheral wall that defines a slot having an enlarged recess and a reduced width opening to the recess. The pin captivation structure includes a tab having an enlarged head and a reduced width neck whereby the tab head can be forced into the enlarged recess of the slot so that the tab neck is received in the reduced width opening of the slot to create a releasable snap-fit engagement that holds the probe tip in the housing.

A second aspect of the invention relates to improved visibility of a portion of the probe that is located adjacent the coating. The probe has a housing having a receiving cavity with an access opening. The probe also has a light transmissive captivation structure that is mounted in the receiving cavity of the housing for communication through the receiving cavity access opening with the exterior of the probe. The probe further includes at least one electrically conductive pin that (1) has a portion captivated in a fixed orientation within the light transmissive captivation structure, (2) has a distal end projecting outwardly of the light transmissive captivation structure for engaging the coating, and (3) is connected with an electrical circuit adapted to provide electrical communication with the processing system. The probe also has a light emitting source in the housing for emitting light through the light transmissive captivation structure along the pin to illuminate the pin distal end. This permits the user to better observe the placement of the probe pin at a desired location on the coating.

According to a presently preferred embodiment of a probe incorporating this second aspect of the invention, the housing is a generally tubular, opaque structure, but the light transmissive captivation structure is molded from a transparent, thermoplastic material, such as polycarbonate, and is drilled to provide a hole or passage in which a portion of the pin is captivated and held in the desired fixed orientation. At least one contact is mounted in the tubular, opaque structure, and the contact is connected with the electrical circuit adapted to provide electrical communication with the processing system. The pin and the light transmissive captivation structure together define an integral unit in the form of a probe tip that has (1) an inner portion that is received in the housing so as to effect engagement between the pin and the contact, and (2) an extending portion that projects from the housing at the receiving cavity access opening. The tip may or may not be designed to be readily removable from the housing by the user.

A third aspect of the invention relates to a probe which uses a pin or pins to engage a coating and which provides better stabilization of the pin or pins. The probe provides electrical communication between the coating and a processing system wherein the processing system determines an attribute of the coating, such as the thickness of the coating, by detection of phenomena resulting from the application of electrical energy to the pin in contact with the coating.

The pin includes (1) a plunger having a shank with a conical distal end that is symmetric about a longitudinal axis and that is adapted to engage the coating, (2) a proximal portion that includes a barrel that receives at least a portion of the plunger in a telescoping relationship to accommodate reciprocation of the plunger in the barrel, and (3) a spring in the barrel for biasing the plunger outwardly.

According to this third aspect of the invention, the probe includes a captivation structure for holding the pin in a fixed orientation in the probe. The captivation structure includes (1) a barrel restraining structure for restraining the barrel of the pin against axial and lateral movement; and (2) a plunger restraining structure that (a) defines a frustoconical seat about an axis that is coincident with the longitudinal axis, and (b) engages the pin plunger shank conical distal end as the plunger is biased outwardly by the spring to provide stabilization of the distal end. The pin(s) and the captivation structure may or may not be designed to be readily removable as an integral unit from the probe and/or incorporate an illumination system.

The above-described invention first aspect or feature (i.e., probe component removability), second aspect or feature (i.e., probe illumination), and third aspect or feature (i.e., pin stabilization) of may be readily incorporated together in one probe. However, if desired, a probe of the present invention may include only a selected one or two of the three aspects or features of the invention.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention, from the claims, and from the accompanying drawings.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, this specification and the accompanying drawings disclose only some specific forms as examples of the invention. The invention is not intended to be limited to the embodiments so described, however. The scope of the invention is pointed out in the appended claims.

For ease of description, the probe of this invention is described in the normal (upright) operating position, and terms such as upper, lower, horizontal, etc., are used with reference to this position. It will be understood, however, that the probe of this invention may be manufactured, stored, transported, used, and sold in an orientation other than the position described.

Figures illustrating the probe show some conventional electrical, mechanical, and structural elements that are known and that will be recognized by one skilled in the art. The detailed descriptions of such elements are not necessary to an understanding of the invention, and accordingly, are herein presented only to the degree necessary to facilitate an understanding of the novel features of the present invention.

The features of the present invention are especially suitable for use in a probe that is part of a system for measuring the thickness of a conductive material on a substrate, such as a coating of copper in a portion of an integrated circuit on a printed circuit board. The features of the present invention are hereinafter described as incorporated in a probe that is designed to be especially suitable for measuring the thickness of a copper coating using conventional resistance or micro-resistance techniques.

The American Society of Testing and Materials (ASTM) has promulgated standards that relate to resistance methods for determining thickness of some materials, and these include ASTM F 39098 and ASTM F 1529—02. The micro-resistance method of thickness measurement is a well-known technique employed in the printed circuit board industry to measure the thickness of copper on printed circuit boards. Conventional micro-resistance techniques for measuring the thickness of a coating of copper on a substrate typically employ a probe which has four, projecting, conductive prongs or pins which can be oriented generally perpendicular to the copper coating so as to readily engage the copper coating in substantially point contact. The pins are oriented in parallel and are spaced apart along a straight line. Each pin has a distal end point for engaging the copper coating. A constant current is maintained between the two outer pins when the pins are in contact with the copper coating. The voltage drop through the copper coating between the two middle pins is measured. The resistance is then calculated by applying Ohm's Law using the known constant current that is passing through the copper coating and using the measured voltage drop. The calculated resistance is then compared to the known relationship of copper resistivity versus thickness to determine the thickness of the measured copper coating. The calculation and thickness measurement comparison are performed automatically in a processing system which (1) is connected to the probe, (2) establishes the current between the two outer pins, and (3) measures the voltage drop signal across the two inner pins.

Conventional instruments employing probes and the micro-resistance method are marketed in the United States of America, among other places, under the model designations SRP-1, SRP-2, and SRP-3 by Oxford (as more particularly identified above in the section entitled “BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART”). Such probes are tethered by a cable to an electronic gauge (i.e., a combined signal processing and power supply unit) containing the processing system for determining the copper coating thickness with the above-discussed micro-resistance method. The conventional processing systems (which include the necessary power supply) employed by such instruments may also be employed with the improved probe of the present invention, and the detailed design and operation of such processing systems form no part of the present invention.

FIG. 1shows a first, preferred embodiment of an improved probe40of the present invention in a normal, generally upright operating orientation wherein the probe40is in contact with a substrate having a coating42with a thickness that is to be measured, and the coating42is illustrated inFIG. 1in a simplified, schematic representation. It is to be realized that the coating42may be a narrow line of copper in an integrated circuit on a portion of a printed circuit board.

The probe40has a bottom or front end for being placed on the coating42to be measured as shown inFIG. 1, and the probe40has a top or rear end with an opening or hole41(FIGS. 3,11, and14) from which a cable44extends for being connected to the electronic gauge (i.e., a combined signal processing and power supply unit) which contains the processing system which also typically includes a power supply and a display or read-out panel and controls. For convenience, such a combined signal processing and power supply unit will be hereinafter referred to simply as the base unit (not illustrated in the Figures). The detailed design and operation of such a base unit form no part of the present invention.

The cable44terminates in a pin connector46which may be of any suitable conventional or special design for connecting to the base unit which contains the processing system (that includes the power supply). In a contemplated, alternate embodiment (not illustrated), a power supply for providing electric current in the copper coating could be a battery mounted directly in the probe40, and the probe40could include a wireless communication system for communicating with the base unit (e.g., “blue tooth” wireless technology). In such a contemplated embodiment, the base unit would then contain only the processing system (incorporating any necessary power supply, display panel, and controls). In another contemplated, alternate embodiment (not illustrated), the probe per se could be made large enough to contain the entire processing system (with power supply (e.g., a battery) so as to eliminate the need for a separate base unit and cable connection (or wireless connection). In yet another contemplated, alternate embodiment, the probe could be fixed within, or be part of, a much larger stationary or portable device containing the processing system (including the power supply, display panel, and controls).

In the illustrated preferred embodiment, the connector46and cable44contain a suitable wiring system defining part of an electrical circuit adapted to provide electrical communication between the probe40and the processing system of the base unit (not illustrated). The wiring system of the cable44extends into the inside of the probe40wherein the cable44is connected with one or more wires as are schematically represented in dashed dot lines48(FIG. 14). In the preferred embodiment of the invention as illustrated, the electric current can be supplied from the base unit through the cable44to the probe40, and a signal corresponding to the voltage drop in the copper coating as detected by the probe40is communicated through the cable44to the base unit. The cable44may be of any suitable conventional or special design incorporating the necessary wires or other electrical conductors. The detailed design and construction of the cable44form no part of the present invention.

The main components of the probe40per se, will next be briefly described. As can be seen inFIG. 3, the main components of the presently preferred embodiment of the probe40include a housing50in the form of a tubular structure or barrel, a printed circuit board52, and a connector53comprising a set of ten contacts54disposed in a contact holder or fixture56that is mounted to the printed circuit board52.

In the preferred embodiment, the contact fixture56(that is part of the connector53and that holds the ten contacts54) is an insulating component molded around, or otherwise capturing, the contacts54. A presently preferred form of the contact54is made from phosphor bronze which is then gold plated. Suitable types of such ten-contact connectors53are sold in the United States of America under the model designation “SMT Surface Mount One-Piece Interface SEI Series” by Samtec U.S.A., having an internet business website at www.samtec.com, and having a post office address of P.O. Box 1147, New Albany, Ind. 47151-1147 U.S.A.

A light source58, preferably in the form of a light-emitting diode (LED)58, is also mounted to the printed circuit board52. The printed circuit board52, to which is mounted the LED58and the connector53, is disposed inside the housing50as described in detail hereinafter. In the preferred embodiment, the housing50is molded from an opaque thermoplastic material, such as the opaque form of the material sold in the United States of America under the trade name or trademark LEXAN by General Electric Company which has a place of business at 3135 Easton Turnpike, Fairfield, Conn., 06828-0001, U.S.A. Other suitable materials may be employed instead.

The printed circuit board52contains conventional electronic circuits which, among other things, establish connections between the cable44and four of the ten contacts54, control current to the LED58, and provide some electrostatic discharge protection. Any specific detailed design and operation of such conventional circuits form no part of the present invention.

At the lower end of the housing50is a probe tip or nose assembly60comprising a transparent probe tip upper part62, a transparent probe tip lower part64which is permanently attached to the upper part62(as with adhesive or other suitable means), and four conductive pins66which each comprises a barrel or sleeve72, a plunger74which is telescopically received within the barrel72, and a compression spring76which biases the plunger74outwardly. As can be seen inFIG. 23, the plunger74of each pin66has an intermediate, reduced diameter portion80below an upper end portion81. The pin barrel72has a reduced diameter, interior bead82located around the reduced diameter portion80of plunger74below the plunger upper end81so as to prevent the plunger74from being removed from the pin barrel72. The pin spring76biases the plunger74outwardly (downwardly as shown inFIG. 23). However, as explained in more detail hereinafter, the pin barrel bead82does not engage the pin plunger top upper end81because the bottom end of the pin plunger74engages the probe tip lower part64at a location that causes the top end of the plunger74to be spaced slightly above the pin barrel bead82(with the spring76being under a small amount of compression). In the illustrated preferred embodiment, the attached assembly of probe tip upper part62and attached probe tip lower part64may be characterized as an electrically insulating, pin captivation structure for holding the pins66in the desired orientation and configuration.

Each pin66functions as an electrically conductive engaging member which includes, among other things, two functional portions: (1) an outwardly projecting distal end (i.e., the pointed, lower end of the plunger74) for contacting the copper coating, and (2) a proximal portion (i.e., upper part of the barrel72) for engaging a contact54(FIG. 16). The presently preferred form of the particular pin66as illustrated inFIG. 23(and in some of the other figures) is sold under the general model designation or trademark “Pogo” pin by Everett Charles Technologies, ECT Headquarters, 700 E. Harrison Avenue, Pomona, Calif. 91767, U.S.A.

FIG. 2Ashows how the assembly of the printed circuit board52, LED58, and fixture56(with the contacts54) is adapted to be mounted by the manufacturer in the cavity defined in the interior of the housing50. For ease of installation, the cable44is typically initially inserted through hole41in the top end of the empty housing50and out of the open bottom end of the housing50so that the cable wiring can be soldered, or otherwise electrically connected, to the printed circuit board52. Thereafter, the cable44, along with the attached printed circuit board52and components thereon, are pulled into the interior of the housing50. Opposite lateral edges of the printed circuit board52are each respectively received within a respective channel90in the housing50as can be seen inFIGS. 10 and 17, as well as inFIG. 13(wherein the printed circuit board52is illustrated in phantom by dashed dot lines).

The integrated circuit on the printed circuit board52and the internal wiring within the housing50which connects the printed circuit board52with the extending portion of the cable44may be characterized as an electrical circuit adapted to provide electrical communication between one or more of the contacts54and the processing system (which may include the power supply) in the base unit (not illustrated).

The LED58may be any suitable conventional or special light-emitting diode. The LED58is connected with leads or wires59(FIG. 3) to the electronic circuit on the printed circuit board52for receiving power which is supplied to the printed circuit board52through the cable44from the base unit (not illustrated). As shown inFIG. 14, the LED leads59are relatively stiff so that they hold their shape to support the LED58in a fixed location projecting outwardly from the printed circuit board52and over the top (inner) end of the probe tip upper part62. In a presently preferred embodiment, the LED58is a conventional, commercially available LED providing a generally white light. A presently preferred LED is the type of LED provided by Marktech Optoelectronics, 120 Broadway, Menands, N.Y., U.S.A., under model designation No. LC374NWH1-30H.

The housing50preferably also includes a label member94(FIG. 3) which may be adhesively secured or snap-fit into a receiving recess96in the exterior surface of the housing50. The label member94may include indicia, such as a model designation, trademark, etc.

With reference toFIG. 2A, the nose assembly or probe tip60(which comprises the pins66contained within the assembled probe tip lower part64and probe tip upper part62) is preferably adapted to be removably (releasably) mounted in the end of the housing50. The probe tip60is preferably designed to cooperate in a snap-fit engagement with the housing50. To this end, the probe tip upper part62includes a tab102(FIGS. 2A and 5). As shown inFIG. 5, the tab102has a slightly enlarged (wider) head104and a very short, reduced width neck106. As shown inFIG. 2A, the housing50is a generally tubular structure having a peripheral wall that defines an internal receiving cavity with an access opening defined by the round opening at the bottom end of the housing50. At the bottom end of the housing50, the peripheral wall of the housing50defines a slot110. At the very bottom edge of the housing50, the slot110has a reduced width opening112. Just slightly inwardly of the reduced width opening112, the slot110has a slightly enlarged recess114.

With reference toFIG. 2A, the tip60can be inserted into the open bottom end of the housing50so that the tip tab102is received in the housing slot110. The slightly enlarged tab head104is defined by slightly arcuate or curved side surfaces which facilitate the elastic spreading or deformation of the housing50as the housing slot reduced width opening112temporarily widens to accommodate longitudinal movement of the tip tab enlarged head104through the opening112and into the adjacent, enlarged recess114of the housing slot110. When the tip60is properly and fully seated within the end of the housing50, the enlarged head104of the tip tab102is snugly received within the housing slot enlarged recess114, and the reduced width neck106of the tip tab102is firmly and snugly received within the housing slot reduced width opening112to create a releasable snap-fit engagement.

The tip60can be readily removed by the user who merely needs to grasp the tip lower part64which projects from the bottom end of the housing50(FIG. 1), and then pull the tip60outwardly with sufficient force to overcome the snap-fit engagement. This allows the user to readily remove and replace a damaged probe tip60. Also, this allows the user to readily change one type of probe tip for another type of probe tip. For example, as will be explained in more detail hereinafter, probe tips60may be provided in different configurations with different features that may be more suitable for a particular application. A different probe tip can be installed into the probe housing50very quickly. This capability improves the versatility of the probe40.

As can be seen inFIGS. 15,16,17,18, and19, the pins66are disposed in the assembled probe tip upper part62and lower part64so that the pin proximal portion or barrel72engages an adjacent contact54. Each contact54has a spring arm120for being engaged by the adjacent pin barrel72. The spring arm120of each contact54is adapted to be elastically deflected inwardly when engaged with the adjacent pin barrel72so as to insure good electrical contact. The engagement between each pin barrel72in the adjacent contact54allows the pin66to be pulled outwardly with the rest of the probe tip assembly (the probe tip upper part62and probe tip part64) by the user when the user wishes to remove the probe tip.

For manufacturing convenience, the probe incorporates the above-described commercially available connector53that has ten contacts54. Only four of the contacts54are employed in the presently preferred embodiment of the probe illustrated, and each of those four contacts54respectively engages an adjacent respective one of the four pin barrels72as can be seen inFIGS. 17–19. The engagement of each pin barrel72with an arm of an adjacent pin54provides good electrical contact while permitting easy removal of the probe tip containing the pins66without requiring the use of a tool or tools.

The design of the nose assembly or tip60provides a very good system for mounting each pin66in a proper orientation and for holding the pin66tightly in position while minimizing lateral movement or wobble of the distal end of the pin that contacts the copper coating. This design is achieved with the use of the pin captivation structure the is defined by the structure of the probe tip upper part62and probe tip lower part64as will next be explained in detail.

The probe tip upper part62and the probe lower part64(FIG. 3) are each preferably individually molded from an electrically insulating material to facilitate manufacturing, and then the two molded parts are adhesively, or otherwise, secured together to form a pin captivation structure (as shown inFIGS. 7,8, and9) for receiving and captivating each of the four pins66as shown inFIGS. 22 and 23. In the presently preferred embodiment, the tip upper part62and the tip lower part64are each molded from a transparent, electrically insulating, non-conductive thermoplastic material, such as transparent polycarbonate. A suitable transparent form of the material is sold in the United States of America under the trade name or trademark LEXAN by General Electric Company which has a place of business at 3135 Easton Turnpike, Fairfield, Conn. 06828-0001, U.S.A. Other suitable materials may be employed instead.

As can be seen inFIGS. 4 and 5, the probe tip upper part62has a generally annular lower portion130defining an internal cavity or recess for receiving upwardly projecting portions of the probe tip lower part64(seeFIGS. 8 and 9). With reference toFIGS. 4 and 5, the probe tip upper part62includes an upper, pin-stabilizing portion132which has four, semi-cylindrical cavities or recesses134(FIG. 4) for each receiving a portion of the pin barrel72as shown inFIG. 15. This allows an oppositely facing, semi-cylindrical side surface of each barrel72to be exposed for contacting an arm120of an adjacent contact54to establish good electrical contact, and this permits removal of the probe tip60by longitudinal withdrawal of the probe tip60from the probe housing50.

As can be seen inFIGS. 15 and 23, an intermediate portion or length of each pin barrel72is entirely surrounded by a central portion136which projects downwardly in the probe tip upper part62to provide a secure captivation of the pin barrel72. This captivation of an intermediate portion of each pin barrel72is accomplished by press-fitting the pin barrel72into a hole or bore138(FIGS. 4,15, and23) that extends through the probe tip upper part62. The hole138is aligned with, and forms a continuation of, the semi-cylindrical cavity134in the upper portion of the probe tip upper part62(FIGS. 4 and 15). In the preferred embodiment illustrated, the components are preferably dimensioned so that the barrels of the pins66each can be press-fit into the probe tip upper part62until the top of each pin barrel72is generally flush with the top end surface of the probe tip upper part62(FIGS. 15 and 23). The preferred dimensional relationship between the outside diameter of each pin barrel72and the internal diameter of its respective receiving bore138in the probe tip upper part62is described in detail hereinafter. In the presently preferred embodiment, the probe tip upper part62is molded with the bores138and cavities134. However, the bores138could be drilled instead.

The probe tip lower part64has a flared configuration owing to an outer shroud140defined by a partially spherical outer surface and a partially spherical inner surface. The shroud140functions as a peripheral platform that projects from the probe housing50(as shown inFIG. 1) when the probe tip is properly installed in the probe housing50. The shroud or peripheral platform140extends laterally around at least a portion of the lengths of the projecting plungers74of the pins66(FIG. 15) to provide support for the probe40when each pin plunger74is engaged with the copper coating and forced against the pin spring76further into the pin barrel72.

As can be seen inFIGS. 1 and 24, the shroud or peripheral platform140defines an open, viewing aperture146to accommodate visual inspection of the pin plungers74on the copper coating when the probe40is supported by the peripheral platform140over the copper coating.

As can be seen inFIGS. 8 and 9, the probe tip lower portion64includes an internal, downwardly projecting wall150which extends, in the preferred embodiment illustrated, to the bottom of the shroud or peripheral platform140. The wall150defines four, multi-diameter bores or passages154as can be seen inFIG. 9. The passages154are each adapted to receive a lower portion of a pin66which is disposed to project through the bottom of the wall150as shown inFIG. 15.

As illustrated inFIG. 24, the top of the probe tip lower part64includes two spaced-apart, partially cylindrical bosses160, and the bosses160are adapted for each being received within the cavity defined inside the lower peripheral wall130of the probe tip upper part62as illustrated inFIGS. 15 and 16. The exterior, partially cylindrical surfaces of the bosses160mate with the interior cylindrical surface of the probe tip upper part lower peripheral wall130. The upper part62and lower part64are adhesively secured together along those mating surfaces. Alternatively, other designs could be employed to facilitate attachment of the probe tip upper part62to the probe tip lower part64.

Further, in an alternate embodiment (not illustrated) the probe tip upper part62and the probe tip lower part64could be connected together with suitable mechanical expedients, including the use of mechanical fasteners, staking, ultrasonic welding, etc. In yet another contemplated, alternate embodiment (not illustrated), the pin captivation structure need not be assembled from two separate pieces (such as probe tip upper part62and probe tip lower part64), and instead, a suitable pin captivation structure could be initially molded as a single, unitary structure (without any internal cavities so as to facilitate ease of molding of such a unitary structure). In yet another contemplated, alternate embodiment (not illustrated), the pin captivation structure could be assembled from three or more separate pieces.

Further details of the preferred design for captivating each of the pins66in the probe tip captivation structure (comprising the probe tip upper part62and probe tip lower part64) will next be explained in detail with reference toFIGS. 20,21, and23. Each probe tip upper part bore138and probe tip lower part passage154are adapted to receive a pin66as shown inFIG. 23. In the particular illustrated embodiment, the barrel72of each pin66has an outside diameter of 0.0420 inch. The probe tip upper part bore138has a smaller diameter A (FIG. 20) of 0.0415 inch. This results in a radial interference of 0.00025 inch (0.0420 inch minus 0.415 inch, divided by 2) which must be accommodated by local deformation of the probe tip upper part62during a press-fit installation of the pin barrel72into the bore138. In the probe tip lower part64, the top end of the passage154is defined by an upper bore156having a diameter B (FIG. 20) of 0.043 inch. Each pin66is installed by press-fitting the pin barrel72into the slightly smaller diameter A of the probe tip upper part bore138, but there is a radial clearance around the lower portion of the pin barrel72in the upper bore156of the probe tip lower part64, and that radial clearance is 0.0005 inch (0.0430 inch minus 0.0420 inch, divided by 2).

Each pin plunger74(FIG. 23) may be characterized as a shank having a distal end conical point or tip170. In the preferred embodiment, the plunger shank has an outside diameter H (FIG. 21) of 0.030 inch above the tip170. Thus, each pin plunger74has a clearance in the upper bore156of the passage154of the probe tip lower part64because the diameter B of the upper bore156is 0.043 inch which is larger than the pin plunger diameter H of 0.030 inch.

The bottom portion of each passage154in the probe tip lower part64is defined by a lower bore172(FIGS. 20,21, and23) having a diameter C of 0.031 inch. Each lower bore172is adapted to receive a plunger74of a pin66. Thus, around the shank of the pin plunger74in the lower bore172(FIG. 21), there is a very small radial clearance of 0.0005 inch (0.031 inch bore diameter minus 0.030 inch plunger diameter, divided by 2).

The radial clearance around the pin plunger74in the upper bore156and the small amount of radial clearance around the lower end of the pin plunger74in the lower bore172are provided to accommodate a relative vertical displacement between the plunger74and the probe tip lower part64. The inventors have determined that precision and accuracy of the copper thickness measurement can be deleteriously affected by lateral displacement of the pin point170which could occur in conventional prior art probe systems prior to, and during, engagement of the pin point with the copper coating. In order to minimize, if not substantially eliminate, significant lateral pin movement which could cause an unwanted decrease in precision and/or accuracy of the measurement, one aspect of the present invention provides a pin plunger restraining structure that includes only a very small clearance in the bore172around the shank of the plunger74so as to limit lateral displacement or wobble, and that also includes a special frustoconical seat180(FIG. 21) for engaging the conical, distal end point170of the pin plunger74(at the bottom end of the lower bore172), to provide an initial, lateral restraint of the tip170. In the particular preferred embodiment illustrated inFIG. 21, the pin point170has a cone angle or conical angle G (FIG. 21) of 60 degrees, and the frustoconical seat180of the probe tip lower part plunger restraining structure has a mating angle F (FIG. 21) of 60 degrees. As shown inFIG. 21, the probe tip lower part frustoconical seat180has a minimum opening diameter D (FIG. 21) at the bottom of the probe tip lower part wall150. In the presently preferred embodiment, the opening diameter D is equal to 0.023 inch, and the frustoconical seat180has a height E (FIG. 21) of 0.0007 inch.

In the preferred embodiment illustrated, the end of the plunger tip170may project between about 0.015 inch and about 0.020 inch downwardly beyond the bottom of the seat180. However, this is not a particularly critical dimension, and the plunger tip170may be designed to project a lesser or greater amount in some applications. This could be accomplished by changing, for example, the tip conical angle G.

Depending upon component sizes and materials, the above-discussed preferred diameter dimensions of the components and the receiving bores may be varied so long as a portion of the pin barrel72is securely captivated and so long as the pin plunger tip170is initially laterally restrained at a predetermined location at the bottom of the probe (as by engagement of the pin tip170with the seat180).

In the preferred embodiment illustrated, the conical distal end or point170is symmetric about the longitudinal axis of the shank of the pin plunger74, and the plunger restraining structure frustoconical seat180is defined about an axis that is coincident with the longitudinal axis of the plunger shank and conical distal end point170. Preferably, the seat angle F and the plunger tip angle G are equal.

In the preferred embodiment, the plunger tip170becomes seated against the plunger restraining structure frustoconical seat180such that the plunger upper end81is spaced slightly above the pin barrel bead82(as can be seen inFIG. 23), and such that the pin spring76is under some slight compression.

This insures that the distal end point tip170of the pin will be properly seated against the frustoconical seat180whenever the probe pin point170is not in contact with the copper coating (or any other object, for that matter). This is important so as to insure that, as the pin point170is brought into contact with the copper coating, the pin point170will be stabilized and will always be in the same location at the bottom of the probe until contact is made between the pin point170and copper coating.

After contact is made between the pin point170and the copper coating, the probe captivation structure wall150and frustoconical seat180are free to continue moving downwardly toward the copper coating relative to the probe plunger74because the small amount of clearance around the plunger74within the lower bore172readily accommodates such relative movement (as the pin spring76compresses slightly further) without permitting significant lateral displacement or wobble. Because the engagement of the frustoconical seating surface180with the point170of the pin plunger74initially provides a predetermined location of the pin point170in the probe, each of the four pin points170will have a fixed location relative to the other pin points at the bottom of the probe just prior to the pin points170contacting the copper coating. This substantially eliminates any significant deviations in pin plunger point position that might otherwise be caused by misalignment of the pin plunger74in the pin barrel72or by pin wobble or deflection that could be encountered with some prior art devices.

The probe tip upper part bore138, probe tip lower part upper bore156, probe tip lower part bore172, and probe tip lower part frustoconical seating surface180together may be characterized as defining a hole or passage for receiving the pin66and for accommodating some relative vertical displacement between the pin plunger74and the rest of the pin (and probe) while at the same time providing an effective stabilizing structure for restraining a portion of the pin barrel74against axial and lateral movement, and while at the same time providing a restraining structure around the plunger conical distal end tip170that minimizes, or substantially eliminates, lateral displacement of the plunger tip170prior to the tip170contacting the copper coating.

Because the tip170of each pin plunger is initially located at the same position in the probe relative to the other pin plunger tips, multiple probe placements on a copper coating for making multiple measurements of that copper coating will have a relatively high precision (i.e., the probe has a relatively good capability for repeatedly measuring the same copper coating to determine a thickness that falls within a predetermined minimum range).

Depending on the configuration of the coating or other material for which the probe is being used to measure the thickness, it may be desirable to have a smaller probe or a larger probe. For example, in some applications, the region or regions of a coating to be measured are very small and/or lie between holes or other features in a printed circuit board that prevents the use of larger probes. On the other hand, if a larger probe can be used, it is typically advantageous to use such a larger probe (one wherein the pins are further apart) because such a larger probe can have better accuracy compared to a smaller probe (one wherein the pins are closer together). In general, the widest pin spread in a probe yields the best accuracy and precision. Therefore, it can be desirable to have a probe design which optionally can accommodate different types of pin configurations. Because the probe tip60(FIG. 2) can be readily removed by the user without a tool or tools, a variety of different types probe tips60can be provided to the user for installation in the probe40. Such other configurations of the probe tip60could have a variety of different pin spacings or could have the same pin spacings.

It may also be desirable to replace a “worn out” probe tip with an identical, new probe tip. In some measurement applications, the probe tip pins can be quickly worn down because the printed circuit boards are slid out of the measurement station before the probe tip has been lifted completely off of the copper coating. The removable probe tip feature of the present invention accommodates easy and rapid probe tip replacement in such situations without requiring re-calibration.

According to another aspect of the present invention, the probe40will accommodate changes of the probe tip60wherein only the configuration of the probe tip lower part64is substantially different.FIGS. 25–30illustrate other designs of a probe tip lower part which are each adapted to be fixedly secured to the same probe tip upper part62that has been previously described with reference toFIGS. 1–24.FIG. 25illustrates a first alternate embodiment of a probe tip lower part64A. That alternate embodiment of the probe tip lower part64A does not have a flared shroud or peripheral platform140like the first probe tip lower part64illustrated inFIG. 24. Rather, the probe tip lower part64A has a partially cylindrical shape which is beveled on one side at surface190as shown inFIGS. 25 and 26.

A second embodiment of the probe tip lower part64B illustrated inFIGS. 28–30has a generally cylindrical configuration without any beveled surface.

Each of the alternate embodiments64A and64B of the probe tip lower part may be employed with a probe tip upper part that is substantially identical with the probe tip upper part62described above with reference toFIGS. 1–23. Each of the alternate embodiments of the probe tip lower parts64A and64B preferably includes a pin captivation feature in the form of a frustoconical seating surface180A (FIGS. 26 and 27for the first alternate embodiment) and180B (FIGS. 29 and 30for the second alternate embodiment). The frustoconical seating surfaces180A and180B are designed to cooperate with a pin conical tip (such as the first embodiment conical tip170illustrated inFIG. 21) in the same manner as has been described above with respect to the first embodiment of the probe.

In the illustrated embodiments, the probe tips are adapted to captivate the pins in a spaced-apart, planar array with the conical pin tips spaced along a straight line. However, in some applications, it may be desirable to have a non-linear arrangement of the pin conical tips. The present invention can accommodate probe pin captivation designs for a variety of pin arrangement configurations.

The probe tip upper part62and all of the probe tip lower part embodiments64,64A, and64B are preferably molded from a transparent thermoplastic material, such as a transparent polycarbonate, to facilitate viewing of the lower ends of the pins and to transmit light from the LED (e.g., LED58described above with reference to the first embodiment of the probe illustrated inFIGS. 1–24). It will be appreciated that the preferred form of the pin captivation structure which comprises the probe tip upper part62and the probe tip lower part64(or64A or64B) is a light transmissive captivation structure that can readily function as a light pipe for facilitating illumination of the pin tips as they are brought into contact with the copper coating so as to help the user properly place the pin tips at the desired locations.

It will be appreciated that the probe of the present invention need not necessarily incorporate all of the features that have been so far described. For example, the probe of the present invention may include a readily removable probe tip or nose assembly60containing a suitable conductive member or members for engaging the coating, but the probe need not also include an LED (or other suitable light source), a light transmissive pin captivation structure, or even pins per se. Alternatively, the probe of the present invention could include a light transmissive pin captivation structure with one pin (or multiple pins) and a light source, but the probe need not also include a removable nose assembly or a special restraint structure for engaging the end of a conical tip of a pin. Similarly, the probe of the present invention may include the novel frustoconical restraint structure for the stabilization of the conical end tip of one or more pins, but the probe need not also include a removable probe nose assembly feature or an illumination feature.

It will be readily apparent from the foregoing detailed description of the invention and from the illustrations thereof that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concepts or principles of this invention.