A process for selective metalization for electrically isolating areas of a substrate is disclosed. The process employs placing microridges onto a surface, the microridge protruding from the plane formed by the surface. The surface, including the microridge, is then metalized and a portion of the metalized microridge, beyond the surface plane is removed. This removal process creates electrically isolated areas without affecting the integrity of the substrate.

FIELD OF THE INVENTION 
This invention relates to a method for preparing electrically isolated 
surfaces and particularly, electrically isolated surfaces for intermeshing 
electrical connector members which employ self-locking tapered elements. 
BACKGROUND OF THE INVENTION 
In the manufacture of electrically conductive members, substrates are 
metalized and portions of the metalized surfaces are then removed to 
create an electrically isolated area on the surface. Typical methods for 
removing the metal coating include etching with various chemical etchants, 
or abrading and grinding by conventional techniques such as sanding or the 
like. 
For example, U.S. Pat. No. 5,071,363 to Reylek et al. ("the '363 patent"), 
which is incorporated by reference herein, discloses electrically isolated 
areas on the tapered elements of the intermeshable members which form 
electrical connectors. These electrically isolated areas avoid accidental 
short circuiting. The intermeshable members typically have bodies 
(substrates) of an electrically insulative material such as polyesters, 
liquid crystal polymers, polyetherimides, polysulfones, acrylics, vinyls, 
polyethylenes and polycarbonates. Once the electrically insulative body, 
with its tapered elements forming the outer surface of the body has been 
made, the body is metalized by depositing a thin film of electrically 
conductive metal onto the outer surface by techniques such as vapor 
deposition or chemical deposition. A thicker layer of the same or 
different electrically conductive metal is then electroplated onto this 
metalized layer. Portions of the metal at the ridges and grooves of the 
surface are then removed by abrasion with a diamond saw, to separate the 
metal surface into segments which are electrically insulated from each 
other. 
While this abrasion method is sufficient for producing the electrically 
isolated areas, there are drawbacks. The major drawback is that the 
abrasion weakens the substrate, as the abrasion process introduces stress 
concentrators below the planar surface of the member. As a result, the 
possibility of the fractures and associated mechanical failures to the 
member increases. 
Another drawback is that abrading lowers the useful service life of saws, 
grinders and abrasives, which are expensive devices (usually involving 
diamonds) due to the nature of the required abrasion. 
SUMMARY OF THE INVENTION 
The present invention overcomes the problems of the prior art by providing 
a method of electrically isolating areas of a substrate without affecting 
the integrity of the substrate. This method includes providing a substrate 
with an electrically insulating outer surface, the outer surface defining 
a plane, providing a microridge on the outer surface, the microridge 
protruding from the surface beyond the surface plane, applying a 
conductive coating to the outer surface, and removing at least a portion 
of the metalized microridge above the surface plane such that a plurality 
of electrically isolated areas are created. 
The invention discloses structures known as microridges. These microridges 
are structures that protrude from the surfaces and have rounded corners at 
points where they are joined to the surface. This structure permits 
removal of the metalized surface without affecting the integrity of the 
substrate by either cutting below the surface plane, or the creation of 
stress concentrations as a result of squared corners.

DETAILED DESCRIPTION OF THE INVENTION 
Turning now to FIG. 1, there is shown a substrate 20 of the prior art. This 
substrate 20 forms the body of an intermeshable member, i.e., the Reylek 
et al. ('363) patent, FIG. 4. The substrate includes an outer surface 22 
of tapered elements 24, the tapered elements 24 forming a plurality of 
linear ridges 26 and grooves 28, and extending the length of the 
substrate. One method for forming this substrate 20 is disclosed in the 
Reylek et al. ('363) patent, from the electrically insulative materials 
disclosed therein. 
FIG. 2 shows the substrate 40 of the present invention. The substrate 40 
includes an outer or major surface 42 of tapered elements 44 forming a 
plurality of linear ridges 46 and grooves 48 extending the length of the 
substrate. Each ridge 46 terminates at a crown 50, preferably having a 
flat surface 52, while each groove 48 terminates in a trough 54, 
preferably having a flat surface 6. At least one centrally positioned 
microridge 60, protrudes from the respective crown and/or trough surfaces 
52, 56 where electrical isolation is desired. 
Preferably, a single microridge 60 protrudes from the crown and/or the 
trough surfaces 52, 56. The respective crown and trough surfaces 52, 56 
define primary surfaces, indicated by broken lines 57, 58. The microridge 
60 protrudes to a point beyond the respective primary surfaces 57, 58. The 
microridge 60 is substantially semicircular in cross section and has 
rounded corners 62, 64 where it contacts and attaches to the crown or 
trough surface 52, 56. Other shapes are also permissible, provided the 
microridge includes rounded corners where it contacts and attaches to the 
crown or trough surface 52, 56. 
Microridges 60 are elongate, elevated, sacrificial structures, protruding 
from the substrate 40. Specifically, microridges comprise, long narrow, 
raised lines or strips having partially curved or polygonal cross-sections 
having rounded corners 62, 64 at points where the microridge 60 joins to 
the outer or major surface 42 of the substrate 40. The use of microridges 
in the inventive process permits the use of common cutting, sawing, or 
abrading processes to affect the facile removal of metal from portions of 
metalized microridges without damaging the stress bearing portions of the 
underlying substrate surface. When such metal removal processes are used 
directly on a metalized substrate surface, without microridges, it is 
possible to undercut the substrate substantially below the primary 
surfaces 57, 58. The resulting cuts, notches and related defects in the 
substrate 40 tend to be points of stress concentration where substrate 
cracking takes place, when the electrical connectors are subjected to 
stress (especially cyclic stress) in the use environment. Such stress 
concentrators are increased when the defects (cuts or notches) have sharp 
corners (angles of 90 degrees or less). The microridges move the cutting 
surface and resulting surface damage out of the plane of tensile stress 
(formed by the primary surfaces 57, 58), that would exist were the 
microridges not added. 
This substrate 40 is formed by the method described in the Reylek et al. 
('363) patent, and reconfiguring the masters disclosed therein to include 
areas corresponding to microridges 60. The microridges 60 could also be 
placed onto the electrically insulative bodies disclosed in the Reylek et 
al. ('363) patent in a separate step. The substrate, having integral 
microridges, could be made by injection molding into a mold configured in 
accordance with FIG. 2 above. The injection molding could also be in two 
steps, one for the substrate and a second microridge molding step. 
Alternatively, the substrate 40 can be extruded and the microridge 
cross-section included as a feature of the extrusion die. In this case, 
the extrusion die functions as the master described in the aforementioned 
Reylek et al. ('363) patent. In accordance with this method, the 
thermoplastic resin is extruded "through" the die as opposed to being 
extruded "onto" the surface of the master. 
The substrates are relatively small and include dimensions in accordance 
with those disclosed in Example 1 and Example 2 of the Reylek et al. 
('363) patent, and the Examples below. The semicircular microridges have a 
radius of approximately 0.01 mm. 
The materials for the substrate 40 preferably include ULTEM 2212R, 
available from the General Electric Company, Fairfield, Conn. Other 
suitable materials include those described in the Reylek et al. ('363) 
patent, including poly(ethylene terephthalate), liquid crystal polymers, 
acrylics, vinyls, polyethylenes and polycarbonates, along with ceramics 
and glasses. While it is preferred that these materials form the entire 
substrate, should design parameters not permit this, these materials need 
only form an electrically insulative surface on a body of a different, 
possibly electrically conducting material. 
The metalized substrate 40 is shown in FIG. 3. Here, the outer surface 42 
of the substrate 40 is preferably coated with a metalized layer 66, 
including a primer or seed layer covered with additional copper layers. 
The primer or seed layer is of palladium metal. This palladium metal 
primer layer is usually coated onto the outer surface 42 of the substrate 
40 by conventional techniques such as the Addiposit.TM. V electroless 
metalization process available from Shipley Co., Newton, Mass. 02162. A 
thin Copper layer, having a thickness of less than 1 .mu.m is then placed 
onto this primer layer by electroless deposition or the like. An outer 
copper layer, approximately 10-30 .mu.m thick is then electroplated over 
the intermediate copper layer. 
While the above described metalizing method is preferred, other metalizing 
techniques, layering combinations and metals can also be used with the 
present invention, depending on the circuitizing operation desired. For 
example, when an electroless metalization process is used to plate the 
intermediate copper layer onto the substrate as described above, the 
microridges could be removed after the priming or seeding layer creating 
step with palladium. Removing this bottom priming or seeding layer 
prevents metal from depositing in these regions. 
In FIG. 4, portions of the metalized microridges 60 have been removed, 
creating electrically isolated areas 68 along the outer or major surface 
42. The substrate 40 has now been circuitized, as the metalized sidewalls 
of the tapered elements 44 are electrically isolated. The specific removal 
methods include sanding to abrade away the metalized ridges and milling 
with diamond-loaded cutting wheels in two passes, one forward pass 
followed by one backward pass. When this milling with diamond-loaded 
cutting wheels was performed, sanding was employed to finish the sides and 
edges, to remove any additional copper particles in the substrate surface 
along with the finishing step of using brushes to remove burrs from the 
tops and bottoms. 
Alternately, the microridges 60 can be designed such that they snap off 
upon metalization. The resultant substrate surface would include 
electrically isolated areas. These snap-off microridges are designed to 
include weakened portions within the microridges, at points above the 
primary surfaces 57, 58, formed by the crown or trough surfaces 52, 56, 
such that the snap-off occurs above the primary surfaces 57, 58, whereby 
the integrity of the substrate remains unaltered. These snap-off 
microridges could be made of the above listed materials by techniques such 
as injection molding or extrusion. 
These removal techniques are such that only the microridges, or portions 
thereof (above the primary surfaces 57, 58), are removed. As a result, the 
mechanical integrity of the substrate is preserved, as removal of the 
microridge 60 does not involve cutting into the main body of the substrate 
40. By avoiding cutting into the main substrate body 40, stress 
concentrators, such as notches, pits and scratches, which weaken the 
substrate material, are not introduced therein. Additionally, the 
microridges 60 expose less surface area for cutting and as such, require 
less cutting force, smaller blades and motors (using less energy) for 
their removal. As a result, complex circuitry can be placed on delicate 
articles, which could not be formed using other methods. 
EXAMPLE-I 
A number of intermeshable, locking taper connectors, having the profile 
shown in FIG. 2 above were made using an injection molding process from 
UTLEM.TM.-2212R-1000, a polyetherimide resin, available from General 
Electric Co., Fairfield, Conn. The microridges at the center of the 
successive crown and trough surfaces had a radius of curvature of 125 
micrometers. The trough width between the bottoms of successive tapered 
elements was 500 micrometers, the corresponding crown width was 575 
micrometers, and the half-angle of the tapered element face was 3 degrees. 
The Addiposit.TM. V electroless metalization process, available from 
Shipley Co., Newton, Mass. 02162 was used to prime the substrate surface 
with a seed layer, which was then electroplated with copper. The tapered 
elements were electrically isolated from one-another by removing a portion 
of the microridges. 
Run 1 
The microridges at the bottom of the troughs were partially removed (about 
75 micrometers were removed) with a diamond saw utilizing a diamond 
wafering blade (Part No. 11-4244 available from Buehler, Lake Bluff, Ill. 
60044). Burrs and trapped debris were removed by first blowing loose 
debris away with clean compressed air followed by brushing with a metal 
bristle brush, and a final blast of compressed air. The lack of electrical 
continuity between all pairs of tapered elements was verified by 
resistance measurements well known to those of ordinary skill in the art. 
Run 2 
The microridges at the top of the crowns were partially removed by abrading 
with fine grit (No. 400) sandpaper. The connectors were de-burred and 
tested as in Run 1. No shorted pairs of elements were observed during 
electrical continuity testing. 
Run 3 
The microridges at the top of the crowns were partially removed by skiving 
off the top portion of the ridge with a razor blade. The connectors were 
de-burred and tested as in Run 1. No shorted pairs of elements were 
observed during electrical continuity testing. 
COMATIVE EXAMPLE-II 
This example shows the efficacy of using microridges to electrically 
isolate contiguous conductive regions. 
Run 4 
The flexural strength of the connectors of Example 1, Run 1 was measured in 
accordance with ASTM C790-92 entitled Flexural Properties of Unreinforced 
and Reinforced Plastic and Electrical Insulating Materials. Test Method-I 
A three-point loading system utilizing center loading on a simply 
supported beam. The support span was 18 millimeters. The load was slowly 
increased until it slightly exceeded 67 Newtons. The connector deflected 
but did not break. 
Run 5 
The microridges were completely removed from a connector, and a cut 75 
micrometers in depth below the surface defined by plane defining the 
bottom of the troughs between successive elements was made using the 
diamond saw of Run 1. When tested using the procedure of Run 4, the 
connector broke into two pieces at a loading of 54 Newtons. 
The results show that making notches or cuts into the substrate surface, 
i.e. below the plane defining the bottom of successive troughs weakens the 
connector. 
While an electrical connector has been described, the method of this 
invention can also be used for making other articles. These articles 
include antennas and conductive tracings over three dimensional 
topographies. 
While embodiments of the present invention have been described so as to 
enable one skilled in the art to practice the techniques of the present 
invention, the preceding description is intended to be exemplary and 
should not be used to limit the scope of the invention, which should be 
determined by reference to the following claims.