Apparatus for effecting electrical connections with multiple contact points

An improved construction is provided for interfacing board type interconnect system apparatus for use in effecting a multiplicity of concurrent, respective, electrical connections with closely spaced, typically irregularly arranged, contactable, electrically conductive zones of a printed circuit board or the like, such as is required, for example, in the testing of such devices. The apparatus employs a preferably laminated assembly of stacked, electrically insulative plates, including support plates pre-drilled to provide a matrix of relatively small and closely spaced holes for mounting spring pin type contactor assemblies and backing plates for physical reinforcement of the support plates and pre-drilled to provide a matrix of relatively larger and less closely spaced openings each communicating with a plurality of the mentioned holes to present a clearance path for electrical leads associated with the contactor assemblies. The construction utilized minimizes the drilling required to produce interfacing boards of requisite physical strength, precision, reliability and versatility for use in effecting a multiplicity of electrical connections with the test points of printed circuit board or similar devices having various arrangements of contactable zones thereon.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to electrical interfacing board apparatus for 
effecting concurrent, respective, forceful engagements to make electrical 
connections with each of a multiplicity of generally coplanar, 
electrically conductive zones arranged in a permissably irregular pattern 
upon an electrical device such as, for example, a printed circuit board to 
be tested. 
The invention is particularly concerned with providing an improved 
construction for such interfacing apparatus of type adaptable for use in 
effecting concurrent, electrical connections with the multitudinous, 
densely spaced and typically irregularly arranged test point zones of 
modern printed circuit boards, of configuration permitting the employment 
of the same interfacing board in the testing of printed circuit boards 
having differing patterns of test point zones, and, perhaps most 
significantly, of nature providing the required strength, precision and 
reliability while remaining technically and economically practicable to 
produce. 
2. Description of the Prior Art 
It has long been the common practice in the testing of printed circuit 
boards and similar devices to use some form of interfacing apparatus for 
effecting the normally temporary, electrical connections required to be 
made between the electrical circuitry of the testing equipment and the 
various electrically conductive zones of the device constituting 
electrical test points. Such interfacing apparatus has typically employed 
a plurality of contactor assemblies, usually of a spring biased pin type, 
for establishing electrically contacting engagement with each of the test 
point zones of the device under test (or some intermediate transition 
assembly for accomplishing a physical coordinate conversion), with each of 
such contactors being coupled by a wire or the like to the testing 
equipment circuitry. 
An early practice in such interfacing apparatus was simply to provide one 
contactor assembly for each test point to be engaged and to mount such 
contactors in appropriate locations on a board or carrier assembly for 
aligning with and engaging the test point zones on a particular type of 
printed circuit boards when the contactor carrying board was suitably 
juxtaposed with the device being tested. Since the test point zones on a 
printed circuit board are typically arranged in an irregular pattern, this 
early approach necessitated the drilling of mounting holes for the 
contactor assemblies in the carrier board in an irregular pattern also. 
Another disadvantage of such approach was that, since the pattern in which 
the contactor assemblies were arranged and mounted on the carrier board 
was usually irregular and matched to the test point pattern of one 
particular type printed circuit board for which the interfacing apparatus 
was specifically designed, it was necessary to provide different 
interfacing apparatuses for each type of printed circuit board to be 
tested and to substitute a different interface apparatus in the testing 
fixture each time a different type of device was to be tested. 
Because of the time, cost and inconvenience factors inherent in the 
above-mentioned early approach, effort was then directed to providing 
interfacing apparatus including an intermediate transition assembly that 
would accomplish physical coordinate conversion between the irregularly 
arranged test point zones of a particular type of printed circuit board 
and a set of logically corresponding contactor assemblies mounted in a 
regular pattern such as at the intersection points of a matrix. The 
Wickersham U.S. Pat. No. 3,654,585 illustrates this technique and 
disclosed an implementation thereof in which the transition assembly was 
in the nature of a board to be interposed between the circuit board under 
test and an array of regularly arranged contactor assemblies; the 
intermediate board was itself fabricated in a manner analogous to that 
employed in printed circuit boards, was provided on one face thereof with 
a set of contacts arranged in an irregular pattern for engaging the test 
point zones of the type of device to be tested, was provided on the 
opposite face thereof with a regularly arranged pattern of contacts to be 
engaged by the array of contactor assemblies, and was further provided 
with electrically conductive means passing through the transition board 
for interconnecting logically corresponding contacts on the opposite faces 
thereof. Subsequently, a refined implementation of such technique was 
commercialized in which the opposed contacts and electrical 
interconnections therebetween associated with the transition board were 
provided by bent electrically conductive pins reciprocably carried by the 
transition board with one end of the pins arranged in an irregular pattern 
to match the pattern of test points on the type of device to be tested and 
the other end of such pins regularly arranged in a matrix for engagement 
by the array of spring pin contactor assemblies. Such coordinate 
conversion transition assembly technique permitted the more economical 
fabrication of interfacing apparatus, since the spring pin contactor 
assemblies with which individual wires leading to the test equipment must 
be associated would be arranged and mounted in a regular matrix pattern. 
However, even with that improvement, the problem of needing to provide a 
different form of transition assembly for each type of printed circuit 
board or similar device to be tested still remained, and, although such 
technique has proved quite satisfactory in applications where relatively 
large quantities of only a limited number of specific device types are to 
be tested during a given time period, the expenses involved in providing 
differing transition assemblies for each type of device to be tested, as 
well as the need for substituting different transition assemblies in the 
testing fixture, continued to present a substantial economic burden for 
applications involving the testing of relatively small quantities of each 
of a number of types of custom designed printed circuit boards. 
Accordingly, it has been recognized and found in practice that the over-all 
economies and convenience considerations in connection with the provision 
of interfacing apparatus for use in testing differing types of printed 
circuit boards or the like could best be served by providing the 
interfacing apparatus with an array of contactor assemblies arranged in a 
regular matrix pattern for engaging the printed circuit board under test 
at a multiplicity of regular intervals across the surface of the latter, 
even though only particular ones of such contactor assemblies would be 
engaging test point zones, while the others would be redundant insofar as 
the testing of each specific type of printed circuit board devices is 
concerned. With such last mentioned approach, however, one form of 
interfacing assembly can be employed in testing a diverse variety of 
specific types of printed circuit boards. Moreover, with the sophisticated 
circuitry available in the testing equipment typically employed in such 
applications, it is a simple matter for the testing equipment to 
electrically select which contactor assemblies it needs to be electrically 
coupled with for purposes of testing each specific type of printed circuit 
board to be handled. It will also be apparent that considerable time, 
expense and inconvenience are saved by this general approach by virtue of 
permitting the drillings necessary for the mounting of the contactor 
assemblies to be carried out in a regular pattern, rather than in an 
irregular pattern as required when each contactor assembly must be located 
to match the position of a corresponding test point zone on a device to be 
tested. 
Concurrent development of the technology of fabrication of printed circuit 
boards themselves has, however, added additional and subtle aspects to the 
problem of providing a full solution to the problem. Briefly, the degree 
of both complexity and miniaturization of circuit paths on printed circuit 
boards have increased substantially, while the areas of circuitry on such 
devices have tended to remain the same or even increase, with the result 
that a typical modern printed circuit board presents a much larger 
multiplicity of test points with which electrical connections must be made 
during testing than was the case with earlier such devices, and such test 
point zones also tend to be smaller and at closer intervals than was the 
case with earlier such devices. This, in turn, necessitates the 
employment, with any interfacing apparatus which is to be adapted for use 
with diverse types of printed circuit boards, of a much larger 
multiplicity of contactor assemblies at much closer spacings than would 
have been required for the testing of most earlier types of printed 
circuit boards. 
The increased number and density of contactor assemblies required in the 
mentioned type of regular array or matrix of same for use in testing 
modern printed circuit boards unexpectedly gives rise, however, to 
problems having mechanical as well as electrical implications in 
connection with the practical implementation of a type of apparatus that 
has heretofore been primarily thought of as being of electrical character. 
The more closely spaced drillings required for the mounting of dense 
matrix of spring pin contactor assemblies in an electrically insulative 
carrier board has significant influence upon the physical strength of that 
board. The engagement force required between the contacting portion of a 
spring pin contactor assembly and the corresponding test point zone on a 
device under test, in order to effect a sufficiently reliable and low 
electrical resistance, electrical contact therebetween, is preferably in 
the range of about 2-8 ounces per contactor assembly. Considering that a 
matrix interval of 0.05 inch between adjacent contactor assemblies will 
dispose about 400 of the latter within each square inch of the carrier 
board, it will be perceived that a force of between about 50 lbs. per 
square inch and 200 lbs. per square inch will be exerted back upon the 
carrier board in the direction of its thickness by the contactor 
assemblies when they are in operative engagement with a device under test. 
When it is further recognized that the contactor assembly carrier board of 
interfacing apparatus will normally be of length and width dimensions of 
at least several inches each in order to be employed in testing typical 
types of printed circuit boards, and that such contactor assembly carrier 
boards must normally be supported primarily along marginal portions 
thereof in order to provide clearance for egress of the multitude of wires 
leading from the individual contactor assemblies to the testing equipment, 
it will be appreciated that the contactor assembly carrier board or other 
assemblage utilized for that purpose must be able to withstand very 
substantial, aggregate, physical forces exerted in what would normally be 
its direction of greatest weakness, not only to avoid possible physical 
breakage, but also to minimize distortion that could adversely affect 
either the alignment thereof required for engagement with small test point 
zones of the device under test or altered electrical relationships between 
the already closely spaced contacting portions of the contactor assemblies 
which might adversely influence the testing results. 
It might seem that a solution to the problem would be provided merely by 
increasing the thickness of the electrically insulative plate to an extent 
sufficient to provide the requisite physical strength. However, that 
approach has been found to be impractical in connection with the drilling 
of the holes through the contactor assembly carrier board required for 
mounting of the spring pin contactor assemblies and providing clearance 
for the connection wires individually leading therefrom, both by virtue of 
the tendency of drill bits to wander or deviate from their intended 
straight course when drilling in very thick plates of material (and 
especially the electrically insulative fiber glass material commonly 
employed in fabricating such boards), as well as the increased tendency 
toward breakage of the very fine bits necessarily employed, when 
attempting to drill through a very thick plate. 
Again, it might appear that a satisfactory solution would be available 
through the mere expedient of separately drilling and then stacking a 
number of thinner plates having corresponding holes therein aligned to 
present the required physical strength in the composite carrier board 
assembly. It has been found, however, that even that approach does not 
alone provide a fully satisfactory solution. First, bearing in mind that a 
typical interfacing assembly for use in testing printed circuit boards of, 
say, 12 inch by 12 inch dimensions, would require the drilling of over 
57,000 holes in each plate in order to provide for a matrix of contactor 
assemblies mounted at 0.05 inch intervals, it will be apparent that the 
amount of precision drilling required can compound very quickly with the 
number of plates to be utilized in a composite carrier board assembly. 
Secondly, with the high density of holes in such an assembly, it has been 
found that the physical strength of the individual plates, and thereby the 
composite assembly, tend to be weakened to an unexpectedly significant 
degree, thus leading to the necessity for employing an undesirable number 
of plates and the concomitant multiplication of the expensive, precision 
drilling operations required. 
It is in this general context of previously inadequately practical 
solutions to the problem of providing economical, reliable, precision and 
versatile interfacing apparatus that the improved construction 
contemplated by this invention has been conceived and developed. 
SUMMARY OF THE INVENTION 
This invention solves the problems previously discussed by providing an 
improved construction for interfacing apparatus for use in effecting 
electrical connections with the test point zones of modern printed circuit 
boards or similar devices, which is both economically and technologically 
practical to produce and utilize. 
The improved apparatus contemplated by my invention can be fabricated and 
assembled with high precision, involves a minimum of precision drilling 
operations and materials consistent with the requirements of the intended 
application, and has been found both reliable and convenient in use. 
My currently preferred form of the improved interfacing apparatus employs a 
composite carrier board assembly formed by stacking and securing together 
a plurality of support plates and a plurality of backing plates. The 
support plates are drilled prior to assembly to provide the relatively 
small and closely spaced holes (of, say, 0.038 inch diameter) for mounting 
an array of contactor assemblies in a matrix pattern at the intersections 
of a 0.05 inch intervalled grid. The reinforcing plates are drilled prior 
to assembly to provide larger and more widely spaced openings (of, say, 
0.078 inch diameter) in a regular matrix pattern at the intersections of a 
0.1 inch intervalled grid. The drilled plates are stacked in a 
predetermined arrangement in which the central axes of the holes in the 
various support plates are aligned with each other, the central axes of 
the openings in the various backing plates are aligned with each other, 
and the central axis of each opening is aligned midway between the central 
axes of four adjacent holes with the proximate extremity of each opening 
partly overlapping the proximate extremity of the four adjacent holes to 
place the latter in communication with the associated opening at the 
interface between the support plates and the backing plates. The larger 
size and spacing of the openings as compared with the holes, as well as 
the offset between their central axes and the partial nature of the 
mentioned overlapping between adjacent extremities of each opening and 
four of the holes, not only minimizes the total number of drilling 
operations required and permits the backing plates to be thicker than the 
support plates, but also provides an enhanced reinforcing relationship in 
which the backing plates offer increased reinforcement for the support 
plates and the number of both of such types of plates required for 
interfacing apparatus of given length and width dimensions is minimized. 
After stacking and securement of the plates in their mentioned 
predetermined relationship, the contactor assemblies with lead wires 
attached thereto are installed by feeding the lead wire down through the 
selected hole and the opening associated with the latter, and the base 
portion of the contactor assembly is press-fitted into the hole. Each of 
the openings provides clearance for the lead wires associated with four 
contactor assemblies. I also prefer to make the support plate which will 
be in facing relationship with the device to be tested somewhat thinner 
than the remaining support plates, in order to facilitate drilling with 
the highest possible precision in such thinner support plate, so that the 
holes therein may serve as an accurate locator for the extremity of the 
base portion of the contactor assemblies nearest the device to be tested, 
thereby further assuring proper alignment of the contactor assemblies in 
substantially perpendicular arrangement to the flat surface of such 
locator support plate facing the device to be tested. 
Further significant details of my improved construction will become clear 
from the more detailed description of my currently preferred embodiment of 
the invention hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A general background concerning the purpose and nature of interfacing 
apparatus of the class with which the invention is concerned, as well as a 
general summary of the primary elements and relationships involved in my 
improved construction have already been provided in earlier sections 
hereof, and the general scope of what I regard as my invention will be 
delineated in the claims that follow. Although those skilled in the art 
will appreciate that various dimensions and other details of the improved 
construction broadly contemplated by the invention may be varied or 
modified according to the particular application involved or other factors 
collateral to the essence of the invention, it remains to more 
specifically illustrate the invention by reference to my currently 
preferred embodiment of improved interfacing apparatus for use in testing 
typical, modern, printed circuit boards, as illustrated and generally 
designated by the reference numeral 10 in the accompanying drawings. 
Various aspects of the improved construction of the interface apparatus 10 
may be conveniently noted in the course of tracing the steps involved in 
its fabrication, and with reference to the various Figures of the drawings 
in an essentially sequential manner. 
Accordingly, FIG. 1 shows in unassembled, exploded view fashion, but in the 
relative ordering relationship they will have when assembled, four 
successive support plates 12, 14, 16 and 18 and two backing plates 20 and 
22. All of the plates 12 et seq. are preferably cut from sheets of G-10 
fiber glass material, which is electrically insulative, and may be, say, 
about 14 inches square for use with a typical size of printed circuit 
boards having an area about 12 inches square bearing test point zones with 
which electrical connections are to be made. The support plates 12, 14, 16 
and 18, when assembled in stacked relationship, present what may be 
referred to as the holding assembly 12 et seq., while the backing plates 
20 and 22, when assembled in stacked relationship, present what may be 
referred to as the reinforcing assembly 20 et seq. It will be observed 
that the support plate 12, also herein called the locator plate, is 
significantly thinner than the other support plates 14, 16 and 18, and 
that the backing plates 20 and 22 are significantly thicker than any of 
the support plates 12, 14, 16 and 18. The preferred thicknesses are 1/8 
inch for the locator plate 12, 1/4 inch for each of the other support 
plates 14, 16 and 18, and 5/8 inch for each of the backing plates 20 and 
22, providing an aggregate thickness when assembled in stacked 
relationship of 7/8 inch for the holding assembly 12 et seq., 11/4 inch 
for the reinforcing assembly 20 et seq., and 21/8 inches for the 
electrically insulative plate portion of the interfacing apparatus 10. It 
will be apparent to those skilled in the art that differing numbers of 
plates, especially the backing plates 20 et seq., may be appropriate where 
the size of the printed circuit boards to be tested or the size or 
spacings of the drillings used depart from those herein noted for the 
embodiment and application being described for illustration. 
Each of the locator plate 12 and the other support plates 14, 16 and 18, 
after cutting thereof to the desired length and width, are then drilled 
adjacent opposite corners thereof with a pair of alignment and tooling 
reference passages 24 and 26 of, say, about 1/4 inch diameter (or slightly 
greater to tightly receive pins of that size), and are further drilled 
with a multiplicity of perforations 28 which respectively align when the 
support plates are subsequently stacked to present a corresponding 
multiplicity of substantially cylindrical holes through the holding 
assembly 12 et seq. The perforations 28 are of a diameter of 0.038 inch 
(or as required for accommodating the type of contactor assemblies to be 
mounted in the holes of the holding assembly 12 et seq.) and are arranged 
in a rectangular matrix pattern (only a portion of which is illustrated in 
the drawings) with their central axes located at the intersection of a 
grid having an interval of preferably 0.05 inch (and certainly not more 
than about 0.1 inch, if modern printed circuit boards are to be 
accommodated). With the preferred spacing interval of 0.05 inch between 
adjacent perforations 28, the density of the holes through the support 
assembly 12 et seq. presented thereby will be 400 holes per square inch. 
The locator plate 12 will be adjacently facing the printed circuit board to 
be tested when the interfacing apparatus 10 is in operative position, and 
it is particularly important for proper alignment of the contactor 
assemblies of the interfacing apparatus 10 with the test point zones of a 
printed circuit board to be tested that the perforations 28 drilled in the 
plate 12 be both located with maximum precision and have their axes as 
nearly perpendicular to the circuit board facing surface of the plate 12 
as possible; it is for this reason that the locator plate 12 is preferably 
thinner than the other support plates 14, 16 and 18, since this 
facilitates greater precision in drilling of the plate 12. 
Similarly, after being cut to the desired length and width, the backing 
plates 20 and 22 are each drilled with a pair of alignment and tooling 
reference passages 24 and 26, like those for the support plates 12 et seq. 
and adapted to align with the latter, and are further drilled with a 
plurality of apertures 30 which respectively align when the backing plates 
are subsequently stacked to present a corresponding plurality of 
substantially cylindrical openings through the reinforcing assembly 20 et 
seq. The apertures 30 are of a diameter of approximately 0.078 inch (or 
about twice that of the holes in the holding assembly 12 et seq.) and are 
arranged in a rectangular matrix pattern (only a portion of which is 
illustrated in the drawings) with their central axes located at the 
intersections of a grid having an interval of twice the grid interval of 
the holes of the holding assembly 12 et seq. or about 0.1 inch in the 
preferred configuration. With the preferred spacing interval of 0.1 inch 
between adjacent apertures 30, the density of the openings through the 
reinforcing assembly 20 et seq. will be 100 openings per square inch. The 
greater diameter of the apertures 30, as compared with the perforations 
28, permits the backing plates 20 et seq. to be much thicker than the 
support plates 12 et seq. without significant adverse effect upon 
drilling. The greater spacing of the apertures 30, as compared with the 
perforations 28, also results in lesser relative weakening of physical 
strength of the backing plates 20 et seq., as compared with the support 
plates 12 et seq., as a result of drilling. It will be understood, of 
course, that the major surfaces of each of the support plates 12 et seq. 
and the major faces of each of the backing plates 20 et seq. are 
substantially flat and substantially parallel to each other, and that the 
central axes of the perforations 28 and of the apertures 30 are 
substantially perpendicular to such major surfaces or faces of the plates 
12 et seq. and the plates 20 et seq. respectively. 
After drilling and cleaning of the support plates 12 et seq. and the 
backing plates 20 et seq., an epoxy or other suitable bonding material is 
applied, as at 32, to a marginal portion about 1/2 inch in width of each 
pair of the major surfaces of the support plates 12 et seq. and major 
faces of the backing plates 20 et seq. which will be interengaged when 
such plates are assembled into their stacked relationship. 
The support plates 12 et seq. and the backing plates are then stacked into 
their predetermined assembled relationship, as depicted in FIG. 2, with 
the backing plate 22 resting on a flat, rigid surface, and with a weight 
or pressure applied atop the locator plate 12 until the epoxy bonding 
material 32 has cured. During such stacking of the plates 12 et seq. and 
20 et seq. for curing of the bonding material 32, tightly fitting pins 34 
are inserted through the passages 24 and 26 of all of the plates, as 
indicated in FIG. 3, to assure that they are stacked in properly aligned 
relationship. When curing has been completed, the plates 12, 14, 16, 18, 
20 and 22 will all have become laminated into a strong and rigid, 
effectively unitary, composite body adapted for employment as a carrier 
board for contactor assemblies. 
After such stacking and lamination of the plates 12, 14, 16, 18, 20 and 22 
is completed, if such additional drilling was not already done at the time 
of the other drilling operations previously discussed, a plurality of 
countersunk mounting bores 36 will be drilled at intervals of about 21/2 
inches around the marginal portion of the laminated body, as shown in FIG. 
3, and the body will be rigidly, but releasably, secured to the metal 
frame portion 38 of the testing fixture in which the interfacing apparatus 
10 is to be used by means of bolts 40 passing through the bores 36 and 
threaded into the frame 38, as shown in FIG. 4. 
Although those skilled in the art will appreciate that the advantages of 
the invention might be imperfectly enjoyed by employing apertures 30 in 
the backing plates 20 et seq. having a different size or locational 
relationship relative to the perforations 28 of the support plates 12 et 
seq. (such as sizing and locating the openings presented by the apertures 
30 in such manner as to overlap with only two or more than four of the 
holes presented by the perforations 28 at their adjacent extremities or so 
as to overlap fully, rather than partially, with the holes they 
communicate with), the previously mentioned relationship of partial 
overlapping of each opening with four holes is my preferred construction 
and is believed to have advantages over the available alternatives. In 
order to better visualize the preferred relationship in such regard, 
reference is made to FIG. 6 and particularly the left half thereof in 
which the holes 42 presented by the aligned perforations 28 and the 
openings 44 presented by the aligned apertures 30 are depicted without any 
contactor assembly therein. The same matter may be further clarified by 
reference to the left half of FIG. 7, which shows the relationship between 
the holes 42 and the openings 44 from the face of the laminated body 
opposite from that depicted in FIG. 6. 
With the laminated body, broadly designated 46 in FIGS. 4 and 5, fully 
fabricated and preferably mounted upon the frame 38, the next step in 
assembly will involve the installation of the contactor assemblies 48. 
Referring particularly to FIG. 5 but incidentally to FIG. 4 also, it will 
be seen that the preferred contactor assemblies 48 are of the conventional 
spring pin type and include an elongate, sleeve-like base portion 50, an 
elongate contacting portion 52 reciprocably extending axially from the 
base portion 50, and spring means 54 within the base portion 50 for 
yieldably biasing the contacting portion 52 outwardly from the base 
portion 50 in an axial direction. Such contactor assemblies 48 may be 
purchased with various types of engagement heads 56 forming a part of the 
contacting portion at the extremity thereof, although my preferred 
construction is to utilize contactor assemblies 48 having a somewhat 
pointed configuration for assuring an efficient electrical coupling 
between each contactor assembly 48 and the test point zone of the printed 
circuit board with which its head 56 will be engaged during operation. 
Although rigid pins could conceivably be employed in place of the 
contactor assemblies 48, the use of the yieldably biased spring pin type 
components for the assemblies 48 is preferred, in order to allow for 
slight irregularities from precise coplanarity of the test point zones of 
the printed circuit boards to be tested. The contactor assemblies 48 are 
formed of metallic, electrical conductive material and are so made as to 
assure good electrical continuity between the head 56, the remainder of 
the contacting portion 52 and the base portion 50 of the assembly 48. 
Although contactor assemblies 48 may be procured in which the contacting 
portions 52 are outwardly biased with various levels of force, the 
preferred construction utilizes contactor assemblies 48 providing biasing 
forces within the middle to upper part of the range of about 2-8 ounces 
per contactor assembly 48. 
As shown in FIG. 5 and also indicated in FIG. 4, each contactor assembly 48 
is provided with a lead wire 58. Each lead wire is preferably insulated 
and has an exposed portion of its conductive means electrically coupled 
with the base portion 50 of the corresponding contactor assembly 48 in 
some suitable manner, such as by crimping of the base portion 50 upon the 
exposed extremity of the conductor part of the wire 58, as indicated at 
60. 
The contactor assemblies 48 are individually installed and mounted in the 
body 46 by passing the distal end of the lead wire 58 first through the 
selected hole 42, thence through the corresponding opening 44 until the 
base portion 50 of the contactor assembly 48 has entered the hole 42. 
Insertion of the base portion 50 is then continued until it is fully 
seated and tightly received within the opening 42, it being understood 
that the holes 42 are of a diameter in relation to the outer diameter of 
the base portion 50 of the contactor assemblies 48 such that the base 
portions 50 will be essentially press-fitted into the holes 42. In the 
preferred construction, a contactor assembly 48 is installed in each of 
the holes 42 to provide a full, rectangular matrix of contactor assemblies 
48, although it will be understood that, if an interfacing assembly 10 was 
to be fabricated with support plates 12 et seq. that had been pre-drilled 
with a full complement of perforations 28 but was to be employed only in 
connection with the testing of printed circuit boards having a lesser area 
in which its test point zones were located, then contactor assemblies 48 
would need to be installed only in an appropriate sub-set of the holes 44. 
In FIG. 6, the four holes 42 at the right center of the Figure are shown as 
having contactor assemblies 48 installed therein, and the four holes 42 at 
the lower right-hand corner of the Figure are depicted as if contactor 
assemblies 48 were provided therein but had been broken away to show the 
manner in which the lead wires 58 make the transition from the hole 42 
into the corresponding opening 44 at the communicating extremities 
thereof. Such transition of the lead wires 58 is also shown from the other 
direction in the openings 44 depicted near the lower right-hand corner of 
the Figure. The overlapping relationship between the holes 42 and the 
openings 44 is also generally indicated in FIG. 5. 
It should be observed that the preferred construction shown and described 
for purposes of illustrating the invention, assuming that a 12-inch by 
12-inch matrix of contactor assemblies 48 is to be required, would involve 
drilling 57,600 small perforations 28 in each of the support plates 12, 
14, 16 and 18 or a total of 230,400 perforations 28, and would require the 
drilling of 14,400 larger openings 44 in each of the backing plates 20 and 
22 or a total of 28,800 apertures 30. Thus, an aggregate of 259,200 
drilling operations would be required. This is, of course, a very 
substantial amount of drilling, but the magnitude thereof appears to be an 
inherent necessity of providing interfacing apparatus 10 of the 
sophisticated type now required for satisfactory testing of modern printed 
circuit boards. One of the significant advantages of the improved 
construction provided by this invention may be perceived by considering 
the amount of drilling that would be required, if the body 46 of the 
interfacing apparatus 10 were to be more conventionally fabricated to even 
a somewhat lesser aggregate thickness of 2 inches by laminating eight 
support plates each of a 1/4 inch thickness and with such plates being 
drilled with the number of perforations 28 required to provide the same 
number of holes 42 for the mounting of a comparable matrix of contactor 
assemblies 48; each such plate would still require 57,600 perforations 28 
per plate for an aggregate of 460,800 perforations 28 for the entire body 
46 made in more conventional fashion, or nearly twice as many drilling 
operations as are required for the improved interfacing apparatus 10 
provided by this invention. Those skilled in the art will also appreciate 
that, with the conventional method of fabrication mentioned, the lesser 
spacing between the perforations 28, as compared with the spacings of the 
apertures 30 employed in the apparatus 10 of this invention, would also 
necessitate the employment of a greater number of plates in the 
conventional construction in order to achieve the same over-all strength 
for the body 46. 
Although it will be clear that various minor changes could be made from a 
number of the details of the preferred construction disclosed for purposes 
of illustrating the invention, without departing from the gist and essence 
of the latter, it is to be understood that the scope of the invention 
should be measured by the claims which follow and should be construed to 
include mechanical equivalents of the novel interfacing apparatus 10 
provided by the invention.