Note: Descriptions are shown in the official language in which they were submitted.
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The invention is in the field of electrical connectors and
more particularly relates to an electrical connector structure and method
of manufacture of same.
In large electronic systems it is well known to support
various circuit boards in a shelf or frame and to provide interconnections
between the various circuit boards by means of appropriate connectors and
back plane wiring. The back plane wiring may itself be provided by a back
plane printed circuit board mounted to one side of the shelt. In addition
to carrying conductor paths the back plane printed circuit board also
includes connector pins. Each of the connector pins is fixed at a
predetermined location and includes a male element protruding from one
side of the back plane printed circuit for connection to a circuit board
which carries a corresponding female receptacle. Manufacture of these
back plane printed circuit boards is similar to that of most circuit
boards. Components, in this case connector pins, are inserted into plated
through holes in the printed circuit board to provide an intermediate
assembly. Thereafter the assembly is ~ypically machine wave soldered to
obtain a final assembly. In order to avoid contaminating precious metal
plated pin contact surfaces, the solder wave is contacted with the side of
the board away from the protruding pins. Solder from the wave migrates
through the plated through holes by capilliary action preferably filling
all voids whereby acceptably reliable back plane structures for electronic
systems are obtained.
More recently the shelves in electronic systems have been
arranged back to back, to reduce the building space required to house such
systems and also to reduce the length of interconnecting circuit paths.
To accommodate this new arrangement, back plane wiring printed circuit
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boards have been required to include connector pins protruding from both
sides of the board. Circuit boards of this type might be more precisely
termed middle plane wiring boards. Unfortunately this structure is not
directly wave solderable without contaminating the connnector pins on one
of the two sides of the board. At First, manually performed hand
soldering was the only means by which suitable middle plane wiring circuit
boards were manufactured for the electronic system with back to back
shelves.
At least two alternative methods to hand soldering in the
production of middle plane circui-t boards have been developed. One
involves wave soldering in the typical manner after connector pins
protruding from the solder exposure side oF the board have been coated
with a solder resist compound. The other involves a placement of a
preformed ring of solder over each pin location on one side of the board
followed by submersion of the board into a hot oil bath to achieve a
reflow soldering. Both these me~hods have proven to be somewhat
unreliable and hence expensive. In the first method, various solder
resist compounds were tried with various degrees of success. However in
manufacturing none of the solder resists consistently provided adequate
protection of precious metal surfaces of the connector pin. The second
method has consistently produced more acceptable results than the first
method. However it relies on hand labour to place each of the solder
rings before the step of oil bath reFlow soldering. As such it has proven
to be only a minor cost saving in comparison to purely manual hand
soldering.
The invention provides for a middle plane wiring board
structure and method of manufacture which are of similar cost and
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reliability as compared to typical back plane wiring board structures and
manufacturing methods.
In accordance with the invention an electrical connector
includes an electrically conductive connector element anchored in a
substrate. The electrically conductive connector element includes an
anchor portion having a body and a plurality of protrusions extending from
the body. The substrate includes an opening therethrough being defined by
a metallic side wall. The anchor portion resides in the opening with at
least one of the terminating surfaces lying against the metallic side
wall. Solder fillets are contiguous with portions of the protrusion and
the metallic side wall. The metallic side wall, the solder fillets, and
the protrusions in combination define a fluid flowable conduit through the
substrate.
A method in accordance with the invention for manufacturing
an electrical connector includes providing an insulating substrate having
a hole formed therethrough, the hole being defined by a metallic
peripheral wall. An electrically conductive connector element is provided
wherein an anchor portion of the connector element includes a body and a
plurality of protrusions extending from the body and being so spaced as to
achieve an interference fit with the peripheral wall upon insertion of the
anchor portion into the hole. The metallic peripheral wall is tinned with
a solder material and squeegeed to remove all but a substantially uniform
thickness of the solder material. The peripheral wall is cooled to less
than a fusion temperature of the solder rnaterial whereafter the anchor
portion is inserted into the hole providing an intermediate assembly
wherein a fluid flowable conduit is defined between the peripheral wall
and the protrusion. A solder fluxing agent is applied by way of the
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conduit and the electrically conductive element and the peripheral wall
are heated to a -temperature above the fusion temperature whereby a
solder fillet is formed between each of the protrusions and the peripheral
wall to provide a finished assembly.
An example embodiment is described with reference to the
accompanying drawings in which:
Figure 1 is a simplified pictorial illustration of a middle
plane wiring board;
Figure 2 is a side elevational view of an electrically
conductive connector element used in the middle plane wiring board in
figure 1 in accordance with the lnvention;
Figure 3 is a sectional side elevation of an opening in the
middle plane wiring board suitable for receiving the connector element in
figure 2;
Figure 4 is a sectional plan view taken through the middle
plane wiring board illustrating an intermediate assembly of the
electrically conductive connector element in figure 2 after insertion into
a hole in the wiring board as illustrated in figure 3; and
Figure 5 is a sectional plan view similar to figure 4 and in
contrast to figure 4 illustrates a final assembly achieved in the middle
plane wiring board by reflow soldering.
Referring to figure 1, the middle plane wiring board
includes an insulating substrate 10. The substrate 10 is provided by any
convenient material known for this purpose by persons skilled in the
manufacture of printed circuit boards (PCBs). Very briefly in the
manufacture of the PCB, metallic land areas are formed on the substrate at
each location at which an electrically conductive connector element 20 is
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required. The land areas are drilled or punched out to form holes through
the substrate. Thereafter the holes are plated with a conductive
material, for example copper, so that each hole is defined by a metallic
peripheral wall which connec-ts the land area on one side of the substrate
with the corresponding land area on the other side of the substrate.
It is common practice to insert the connector elements 20 such that each
is retained by an interference fit. Thereafter at least one side of -the
PCB is subjected to a soldering process l;o firmly fix the connector
elements 20. The PCB in figure 1 as thus far discussed is exemplary of
commonly practiced manufacturing methods in the electronic industry.
However as previously mentioned, typical machine process soldering methods
are not conveniently applicable in the case where the connector elements
20 protrude on both sides of the substrate 10, as in the case of the
middle plane wiring board in figure 1.
Figures 2 - 5 of the drawings are in substance scale
representations of the example embodiment magnified about 74 times for
convenience of illustration.
In figure 2 the connector element 20 is shown to have an
anchor portion 22 with contact portions 21 of rectangular cross-section
extending therefrom. The contact portions 21 are broken for convenience
of illustration. The anchor portion 22 includes a body 23 and protruding
ribs 24, 25, 26 and 27, extending therefrom to respective terminating
surfaces 24a, 25a~ 26a and 27a. The rib 27 and its terminating surf`ace
are hidden from view in figure 2 but are visible in cross-section with
reference to figure 4. Connector elements similar to that in figure 2 are
commonly used in the electronic industry.
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A novel structure wherein substantially only the terminating
surfaces of the ribs are joined to the metallic peripheral wall is
achieved in accordance with the invention. Figure 3 illustrates in detail
a hole structured at 11 in the substrate 10. To obtain the hole structure
substrate material 12 and copper land areas 15 and 16 are drilled. The
land areas and the peripheral wall are then copper plated to obtain a
plated through hole structure defined by a copper peripheral wall 13. The
copper wall 13 is then tinned to have a thin solder covering 14.
In one example the process of tinning includes steps of
submerging the PCB into molten solder. The PCB is then withdrawn from the
molten solder by way of an air blast squeegeeing apparatus, sometimes
referred to as an air knife9 which removes all but a very thin layer of
solder from the copper. For example in a case where a plated through hole
is of a diameter of between 0.03 and 0.05 inches, a solder layer of about
0.001 inches is satisfactory. After the PCB has cooled to below the
fusion temperature of the solder, the connector element 20 is inserted
such that the anchor portion is in interference fit with the copper wall
13. Figure 4 illustrates a typical cross-section view of an intermediate
assembly of the connector element in the hole 11~ The terminating
surfaces 24a, 25a, 26a and 27a are all in substantially gas tight contact
with the copper wall 13, the solder coating 14 in the contact area having
been stripped away during insertion, and the copper wall and the substrate
material adjacent each of the terminating surfaces having yielded slightly
to accommodate the anchor portion. At this point in the assembly method
four clear conduits 11a, 11b, llc and 11d are defined by the solder layer
14 and the anchor portion 22. The final steps in the assembly process are
that of fluxing and reflow soldering~ Fluxing is achieved by any
convenient means which will cause a solder flux material to flow into the
conduits 11a - 11d either at the moment of flux application or later
during the reflow soldering step. The reflow soldering step may be
accomplished by any of various heating methods which cause the
temperature of the plate through hole and the connector element 20 to
exceed the fusion temperature oF the solder material. For example
exposure of the PCB, while in a substantially calm or stagnant atmosphere,
to radiant energy in arange extendiny through the infrared and visible
spectrums has been found to produce a very satisfactory solder reflow,
obtaining a structure similar to the structure illustrated in figure 5.
Here the solder layer 14 is shown to have virtually disappeared, having
been concentrated into solder fillets 18 which firmly attach the
protruding ribs 24 - 27 to the copper wall 13. Substantially all the
solder present is concentrated in the fillets 18, leaving the contact
surfaces of the contact element 21 without solder contamination, and
typically leaving all of the conduits 11a - 11d substantially intact.
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