This invention relates to an electrical contact in accordance with the generic clause of claim 1.
Modern electronic apparatus makes extensive use of printed circuit boards employing plated-through-holes (PTH). As an alternative to soldering contacts in these holes, it has been proposed to use contacts which engage the hole by friction only. Such contacts generally employ a compliant section for engagement to provide good mechanical and electrical contact. It is desirable that minimum damage be done to the PTH so that such contacts can be removed and replaced. The compliant contacts generally available take several forms: the "eye-of-the-needle" approach, as shown in U.S. Pat. Nos. 3,545,080; 3,634,819; and 4,206,964; the "split beam" approach, shown in U.S. Pat. Nos. 4,066,326; 4,186,982; the opposed "C" sections shown in U.S. Pat. No. 4,701, 140: and the single "C" section, shown in U.S. Pat. Nos. 3,783,433; 4,017,143; 4,076,356; and 4,166,667.
While some of these techniques work to a greater or lesser extent, all have one or more problems, such as cost of making; failure to form a good gas tight seal with the PTH; difficulty of insertion or removal; or, when used in high numbers in thin printed circuit boards, a tendency to warp the boards because of the pressure they exert on the apertures.
Document EP-A-0 208 500 describes an electrical press-fit contact whereby said contact includes a compliant section of a substantially "C"-shaped cross-section and comprises first an second arm portions with a base portion therebetween, whereby the thickness of the compliant section increases steadily from the base portion to the arm portion such that the center of the base portion is of least thickness to form a hinge about which a first and second arm portion maybe preferentially deflected.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance electrical connection in plated-through-holes.
Yet another object of the invention is the provision of an electrical contact for PTH's which achieves the above objects and, additionally, provides ease of insertion and removal with minimal plating damage.
These objects are accomplished with an electrical contact according to claim 1.
The thinner, or relieved section of such a contact, allows for more deflection of the arms. As the ends deflect, so does the thinner relieved area of the bight. The contact can be formed by standard stamping and swaging techniques at a competitive cost.
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.
Referring now to the drawings with greater particularity, there is shown in Fig. 1 an electrical contact 10 having a body 12 with a longitudinal axis 14. First portion 16 and second portion 18 are separated by and connected to a compliant portion 20. The compliant portion 20 has a generally "C" shaped cross-section, more clearly seen in Fig. 2, which is formed from opposed arms 22 and 24 which extend from a joined bight 26. The arms 22 and 24 have a given, substantially uniform thickness, which can be, e.g., 0,20 - 0,23mm (0.008 - 0.009 inches), for a major part of their length. The free ends 28 of the arms can be radiused or beveled, as shown.
The joined bight 26 has a thickness which is less than the thickness of the arms, e.g., about 0,02 - 0,08mm (0.001 - 0.003 inches) less, thus providing more evenly distributed stresses about the plated-through-hole or aperture 30 in the printed circuit board 32. The aperture 30 can have an electrically conductive coating 33 thereon. This more even distribution of forces contributes to less hole deformation and, therefore, less accumulated stresses in the printed circuit board, which causes less warpage.
Further, this configuration provides greater contact surface area to the aperture 30 because the thinner portion of the bight more readily conforms to the aperture.
Preferably, the contact can be made by stamping from sheet stock of phos-bronze having a thickness of 0,5mm (0.020 inches).
The bight can be thinned by coining or swaging to a thickness of about 0,02mm (0.001 inches) less than the arms. When the "C" section is formed it typically will have a diameter of 1,17 ± 0,02mm (0.046 ± 0.001 inches) and will be received within apertures having diameters of from 0,94 - 1.09mm (0.037 to 0.043 inches).