Compliant Pin

This invention relates generally to the joining of electrical connectors to circuit baords and, more particularly, to the construction of the transition zone adjacent the compliant region to provide a low resistance electrical connection between a compliant pin and the side walls of a hole in a circuit board without rupturing the side walls of the hole or overstressing the pin.

In order to provide a compliant pin for multiple use it is desirable to have a compliant pin that does not damage the side walls of the circuit board hole during insertion of the pin into the hole. That is, insertion of the compliant pin should not physically damage the side walls of the hole since a rupture of the side walls of the hole may lead to eventual failure of the low resistance connection between the pin and the side walls of the hole. Yet the compliant pin should be held sufficiently tight so as not to be easily withdrawn. In addition, the compliant pin should be able to withstand vibration forces without breakages. Unfortunately, it has been found that some prior art compliant pins that can withstand vibration forces damage the hole during insertion of the pin in the circuit board. Still other prior art compliant pins that do not damage the hole during insertion of the pin into the circuit board are not capable of withstanding vibration forces.

We have discovered a compliant pin structure which can withstand vibration forces yet does not damage the hole side walls during insertion of the pin into the circuit board.

Briefly, the invention comprises a compliant pin having a transition zone and a compliant region with the transition zone characterized by a compliant region extending into the transition zone so that upon insertion of the compliant pin into an opening in a circuit board the opening in the circuit board is required to partially expand before the compliant region begins to compress from contact with the side walls of the opening in the circuit board.

FIG. 1 is a plan view of a connector embodying the invention;

FIG. 2 is a side elevation taken on lines 2--2 of FIG. 1;

FIG. 3 is a vertical section showing a typical application of the FIG. 1 connection;

FIG. 4 is an enlarged section taken on lines 4--4 of FIG. 3;

FIG. 5 is an enlarged fragmentary side view of the grooved portion of the FIG. 1 connector pin;

FIG. 6 is a sectional view taken on lines 6--6 of FIG. 5;

FIG. 7 is a sectional view taken on lines 7--7 of FIG. 5;

FIG. 8 is a sectional view taken on lines 8--8 of FIG. 5;

FIG. 9 is a detailed view of the transition zone;

FIG. 10 is a sectional view taken along line 10--10 of FIG. 9; and

FIG. 11 is a sectional view taken along line 11--11 of FIG. 9.

In FIGS. 1 and 2 a contact or connector pin 10 is shown to comprise an axially elongated flat member 12. Member 12 includes a first section 12a, a wire wrap post section 12b, an intermediate compliant section 12c, a step shoulder section 12d which joins sections 12a and 12b. Sections 12a and 12b are shown in FIG. 1 to have the same width, which is less than the width of compliant section 12c. Located in compliant section 12c is a transition zone 100 which physically engages the hole side walls in a circuit board prior to the hole side walls engaging the compliant region in compliant section 12c. FIG. 1 shows that during stamping formation of pin 10 the opposite ends of pin 10 may be joined to elongated holding strips 11a and 11b by narrowed break-off connections 110 and 111.

Located in pin 10 is a step shoulder 13 which is formed at the junction of sections 12c and 12d. Step shoulder 13 is adapted to engage the printed circuit backplane board 14 or ring 15a (FIG. 3) to thereby limit the insertion of pin 10 into the board. FIG. 3 shows two connectors 10 inserted through openings or holes 16 which comprise a circular electrically conductive cylinder 15b.

FIG. 4 and FIG. 8 show compliant pin section 12c has opposite outer surfaces 19 and 20 forcibly gripping the inside surfaces of conductive cylinder 15b as pin 10 is inserted into hole 16 in cylinder 15b. In the example shown in FIGS. 4-8 compliant section 12c has convex opposite outer surfaces 19 and 20 with a radius of curvature generally the same as the radius of curvature of circular hole 10. Outer surfaces 19 and 20 forcibly and frictionally grip the inside of cylinder 15b upon insertion of compliant section 12c into cylinder 15b as compliant section 12c compresses inward so that the outer surfaces 19 and 20 on the compliant pin section 12c move from the broken line positions 19a and 20a to the positions indicated in FIG. 4. In the embodiment shown in FIG. 4 the mating surfaces of both pin 12 and cylinder 15b distribute their grip loading over a relatively large contact area, to thereby provide good electrical contact without scoring or damaging the interior side wall surfaces of cylinder 15b.

In the embodiment shown in FIGS. 5-8 pin 10 includes a compliant region 12c having at least one elongated groove 21 located in the side thereof, groove 21 extends axially of pin 10 and is configured to locally weaken pin 10 so that at least one flexure 40 is formed by pin 10 to extend and along the length of groove 12. Flexure 40 (FIG. 8) is adapted to resiliently flex in response to insertion of compliant pin 10 into the circuit board 14. Located on the surface opposite groove 21 is a second groove 22. Grooves 21 and 22 which are located in opposite sides 23 and 24 of compliant section 12c give the pin cross section a generally Z-shape (FIG. 8). Each groove has opposite side walls 25 and 26 forming a generally V-shaped groove cross section along the major length of each groove and in planes normal to the axis of pin 10. FIG. 8 shows the bottom 29 of grooves 21 and 22 are generally concavely radiused. Generally, the depth of each groove is such as to accommodate relative movement of walls 25 and 26 toward one another in response to insertion of pin 10 into a circuit board. In the embodiment shown in FIG. 4 the full depth of each groove is greater than one-half the thickness of the section 12c between sides 23 and 24 but less than three-quarters of the thickness of section 12c.

FIG. 8 shows flexure 40 formed between grooves 21 and 22 to define a plane 41 that extends at an angle .alpha. relative to flat sides 23 and 24. In general, the angle .alpha. is between 45.degree. and 75.degree. in the unflexed condition. In the flexed condition (FIG. 4) flexure 40 has an S-shape, wall 25 is concave, wall 26 is concave; whereas in the unflexed condition (FIG. 8) walls 25 and 26 are generally flat. The center of flexure 40, designated by reference numeral 28, lies approximately midway between crests 12a' and 20a' of surfaces 19 and 20.

FIGS. 6-8 show that the depth of grooves 21 and 22 progressively increases along the apex 31. Likewise at the opposite end of grooves 21 and 22 the depth of grooves 21 and 22 progressively increases along the apex 33 until it is at the full groove depth indicated by apex 29. In the embodiment shown the shape of both grooves 21 and 22 are similar or identical. Apex 31 and 33 concavely merge at junctions 31a and 33a with groove walls 25 and 26.

The outer radiused surface of compliant section 12b prevents gouging of surface of a hole and also distributes the compression loading over the entire surface of the pin and the opening. Note, the leading ends of groove 22 have a progressively increased depth to allow deflection to occur progressively. In this regard too large an angle between groove walls 25 and 26 would overstress the material during manufacture and could cause fracture of the metal while two small an angle would fail to develop forces that act throughout the length of the pin. Note also the concavely rounded edges 42, 43, 44 and 45 between outer surfaces 19 and 20 and sides 23 and 24.

Referring to FIG. 9 reference numeral 10 identifies an enlarged view of a preferred embodiment of a compliant pin 10. Compliant pin 10 can be inserted into a circuit board without damaging the circuit board receptacle, yet permits the pin to withstand vibration forces. Compliant pin 10 includes a front straight section 101 of thickness t.sub.1 and a compliant section 12c of thickness t.sub.2. Located on one side of pin 10 is elongated groove 21 which terminates at a radiused apex 104. Similarly, located on the opposite side of pin 10 there is a second elongated groove 22 that terminates at a radiused apex 120 with radiused apex 120 terminating a distance t.sub.0 ahead of radiused apex 104. The off-setting of the apex of grooves 21 and 22 is believed to distribute the stress from the stamping over a large area so as to reduce the likelihood that pin 10 will break during usage. Similarly, the apex 104 and 120 are also radiused to distribute the stress from stamping the pin over a larger area and thus is believed to also contribute to reducing the likelihood that the pin will not break during usage. Typically, it has been found that if t.sub.0 is 0.002" or more it is sufficient to enhance the ability of the pin to withstand a high vibration environment; however, a minimum dimensional offset of 0.005" to 0.007" is preferred.

Pin 10 is also preferably provided with radiused surfaces at the juncture of the outer plane surfaces on pin 10. That is, the radiused surface juncture of the compliant region are indicated by reference numerals 122, 123, 124, 125, 126 and 127. It is believed that in regions in which pin 10 goes from one dimension to another the juncture of the surfaces should be smooth and radiused rather than abrupt since abrupt surfaces may provide a starting place for pin breakage when the pin is subjected to vibration.

In addition, it is also believed that to further enhance the resisting of the pin to fracture the bottom of groove 22 should be provided with a radiused section 128 that blends the front portion of groove 22 with the bottom portion of groove 22 (FIG. 10). Similarly, the front portion of groove 21 is radiused to the bottom of groove 21.

It should be appreciated that to make a usable pin may not require the radiusing of the juncture of all the pin surfaces described herein; however, it is believed that the more regular and smooth the surfaces and the more widely disbursed the stress points, the more likely the pin is able to be subjected to vibration forces without fracture.

FIG. 11 shows a sectional view of pin 10 with radiused surfaces 130 and 131 located in the converging portion of the apex of grooves 21 and 22.

Elongated grooves 21 and 22 as previously described provide a compliant region 12c on pin 12 which can be compressed by insertion of pin 10 into a circuit board. Transition region 100 which is located on the top and bottom of pin 10 has a length L and forms a first upper and lower transition angle .theta..sub.1, with respect to the upper and lower outer flat surface of front section 101 and a second upper and lower transition angle .theta..sub.2 with respect to the upper and lower outer flat surface of front section 101. Transition region 100 contains three distinct zones. A guide zone A which has a maximum dimension t.sub.3. In guide zone A either the upper outer surfaces 100a or 100d guide pin 10 into alignment with a hole in a circuit board. Thus, in guide zone A it is either one of the other of outer surfaces 100a or 100d that come into contact with the hole as the pin is inserted into the board since the maximum dimension t.sub.3 of guide zone A is less than the minimum dimension of the hole in the circuit board. In interface zone B there is an outer surface 100b and 100e which ranges from a minimum dimension t.sub.3 to a maximum dimension t.sub.4. Interface zone B produces a mechanical interface region between the side walls of the hole and the outer surfaces of pin 10 since opposite surfaces 100b and 100e simultaneously engage the hole in the circuit board. While simultaneous contact of pin 10 begins on a definite area the mechanical interface region is defined as a zone on pin 10 to indicate that the point of simultaneous contact of opposite surfaces 100e and 100b with the hole in the board may occur somewhere in zone B depending on the hole size. For example, with a hole of specified minimum dimension the side walls of the hole would engage outer surface 100e and 100b at the dimension t.sub.3 while a hole of specified maximum dimension the hole would engage outer surface 100e and 100b at dimension t.sub.4. The length of interface zone B is primarily determined by the specified tolerance of the holes in the board since in practice the dimensions of the pins are kept within tolerance that are usually an order of magnitude less than the tolerances of the holes in the circuit boards.

In deforming zone C the outer surface 100c and 100f are in intimate physical contact with the hole in the circuit board. Typically, the hole size in a circuit board may be 0.005" to 0.010" smaller than the compliant pin dimension t.sub.2. In addition, the receptacle forming the hole in the circuit board is generally less deformable than the pin although a certain limited amount of deformation occurs. In deforming zone C the upper and lower outer surfaces 100c and 100f engage the side walls of the hole and are forced inward as the compliant pin 10 is forced into the hole in the circuit board. It will be noted that the compliant region formed by grooves 21 and 22 extends through deforming zone C and substantially through interface zone B. While it is not fully understood, it has been discovered that one factor affecting the ability of the pin to prevent hole damage is having the beginning of the compliant region extending through deforming zone C and substantially through the interface zone B while maintaining the transition angles .theta. approximately 15.degree. or less. It has also been found that the incident of pin failure due to vibration forces has been virtually eliminated even if the transition zone of the pin is deformed during the insertion process. While the mechanism is not fully understood, it was noted that the transition zones with larger transition angles often had minute fractures after the pin had been inserted into the circuit board. That is, when the angle .theta. was sufficiently large the process of insertion of the pin into the hole in the board probably produced minute metal fractures or weak spots that made the pins more susceptible to breakage during vibration testing. In the present embodiment it is believed the increasing of the taper or holding the transition angles .theta. at approximately 15.degree. or less together with extending the beginning of the compliant region into the interface zone permits the hole in the board to partially expand before the compliant region begins to compress. This coaction of hole expansion followed by compliant region compression has apparently eliminated the minute fracture in the pin which leads to pin failure during vibration testing. In general, by vibration testing it is meant that the pins must withstand 30 gs at a frequency of 10-2000 hertz for at least three 20 minute periods in each of the coordinate axes. In addition, the pin should be able to withstand 30 minutes of random vibration in each axis with the vibrations having rms value of approximately 16 gs.

Thus, the invention is characterized by having a compliant region which intercepts the hole in the board at sufficiently small angle so that insertion of the pin into the circuit board does not produce fractures in the metal pin. While the angle may vary with different materials and different hole sizes the following is a typical example of a pin size, hole size and taper which do not produce metal fracture upon insertion of the pin into the hole of the circuit board:

The pin was comprised of a metal alloy of phosphor bronze and was designed to fit in a hole in a board having a hole dimension of 0.037" to 0.043", the t.sub.2 compliant section of the pin was 0.0485" and the front section dimension t.sub.1 of pin was 0.025". The angle of taper .theta. was approximately 15.degree. . The board was made of standard circuit board material which is commercially available under the designation G-10. The thickness of the board was 0.125" and the hole in the board was plated with copper to a thickness of 0.0015". Located on the copper was a 0.0003" coating of solder.

240 pins were inserted into holes in a board and subjected to the above described vibration testing. None of the pins broke during vibration and none of the holes in the circuit board showed damage due to insertion of the pin into the hole.

While the aforementioned compliant region has been illustrated as being formed by elongated recesses located on opposite sides of the surface of the compliant pin, it is envisioned other compliant regions could equally well be used with our invention.