GB2032827A

GB2032827A - Method of mounting a lug- receiving and supporting electrical contact

Info

Publication number: GB2032827A
Application number: GB7932285A
Authority: GB
Original assignee: Bunker Ramo Corp
Current assignee: Bunker Ramo Corp
Priority date: 1978-09-20
Filing date: 1979-09-18
Publication date: 1980-05-14
Also published as: FR2437141B1; SE7907723L; NL7906952A; DE2938038A1; FR2437141A1; JPS5555597A

Abstract

A lug-receiving and supporting contact in a transverse hole in a printed circuit board comprises a generally U-shaped contact element 1 having arms which open toward a lug- receiving end and a bight portion 4 which defines a terminal end. The latter is inserted into the hole 30 in the printed circuit board until it emerges beyond a metallized region 32 thereof. A non-solderable rod 33 is then inserted into the lug-receiving end of the contact element, and solder 34 is deposited about the terminal end and about a portion of the non- solderable rod exposed at the lateral side of the terminal end. Finally, the non-solderable rod is removed from the contact element leaving a receptacle of substantial depth for receiving the connecting lug of an electronic component. The non- solderable rod may be one of a plurality arranged to support and position a plurality of contact elements. <IMAGE>

Description

SPECIFICATION Method of mounting a lug-receiving and supporting contact, and structure produced thereby TECHNICAL FIELD This invention relates to the field of contacts for electronic components, and in particular to a contact which can be mounted in a printed circuit board, and in combination with the circuit board, forms a lug-receiving and supporting contact for a removable electronic component.

BACKGROUND OF THE PRIOR ART It is common in the electronic industry to mount circuit components in contacts on printed circuit boards in a manner that the components can be easily removed for repair or replacement. This is particularly true for electronic apparatuses which contain printed circuit boards carrying a number of integrated circuit packages thereon. Some electronic apparatuses are constructed by placing the terminal lugs of an integrated circuit through holes in the printed circuit board and soldering the tips of the lugs directly to the board. This has the obvious disadvantage of potentially destroying the integrated circuit upon attempting to remove it from the board.

There are known printed circuit supports for electronic components. A typical support has an active contact portion for receiving a lug of an electronic component, and a connecting end provided to be introduced into the hole of a printed circuit board and soldered to the board, i.e.

to the metallized face of the printed circuit board, using standard soldering techniques. These supports are generally provided with means which prevent the solder from flowing through the contact and toward the active contact portion which would otherwise restrict the introduction of the connecting lug of the electronic component.

However, these types of contacts prevent maximum penetration of the contacting lug of the component into the contact element and consequently result in the component mounted off the board adding to the bulk of the completed printed circuit board. Among this type of known supports is one described in German Patent No.

2,104,971 relating to a tubular component support which has, in its central portion, a teflon stopper which seals the tube and opposes the passage of solder. Another German Patent No.

2,053,568 describes a component support having a contact portion comprising a resilient active contact of U-shape, and a connection end which is formed by a small solid extension of the active contact.

Equally known in the prior art are supports made in the form of a closed tube the closed end of which is inserted into the printed circuit board and soldered into place. The closed end prevents solder from being introduced into the active contacting portion and interfering with the connecting lug of the electronic component. This type of support is described, for example, in French Patent No. 2,322,465. It consists of a tubular sleeve introduced into the hole of a printed circuit board and having, at its end opposite the closed end, a retaining means for making releasable connection to the connecting lug of an electronic component. Although this embodiment permits the component to be fully inserted and thereby reduce the bulk of the completed printed circuit board, its cost is high and often prohibitive in the production of small inexpensive electronic devices.

BRIEF SUMMARY OF THE INVENTION The present invention overcomes the shortcomings of the above-noted prior art contacts by providing a method for economically fabricating a support for removable electronic components, such support permitting an effective jointing of electronic components to a printed circuit board while maintaining a minimum height reduction of the components above the board. The present invention relates not only to a method of producing a lug-receiving and supporting contact for printed circuit boards, but also relates to the lug-receiving and supporting contact structure itself and to a contact mounting implement for carrying out the method.

In accordance with one aspect of the invention, there is provided a method of mounting a lugreceiving and supporting contact in a transverse hole in a printed circuit board having a metallized region on one side thereof surrounding the hole. A generally U-shaped lug-receiving contact is provided having arms which open toward a lugreceiving end and having a bight portion which defines a terminal end for the contact. The terminal end is inserted into the hole in the printed circuit board from the side of the board opposite the metallized region until it emerges beyond the metallized region. A non-solderabie rod is then inserted into the lug-receiving end of the contact to fill the space between the contact arms.With the non-solderable rod in place, solder is deposited about the terminal end and about a portion of the non-solderable rod exposed at the lateral side of the terminal end, using known soldering techniques. Finally, the non-solderable rod is removed from the contact leaving a receptacle of substantial depth for receiving the connecting lug of an electronic component.

Preferably, the rod for insertion into the contact during the soldering step is selected to have the shape and dimensions similar to that of a lug to be inserted in the contact.

The lug-receiving and supporting contact structure used in the method described above includes a portion of the printed circuit board as a part of the complete structure. The generally Ushaped lug-receiving contact has a bight portion extending below the metallized region of the printed circuit board and an active terminal portion above the printed circuit board. A deposit of solder covers the exterior surface and side edges of the bight portion which extends beyond the metallized region and covers the metallized region surrounding the hole, leaving substantially the entire inner surface of the bight portion solderfree.The solder is thus restricted to the extreme lower depths of the lug-receiving and supporting contact structure, while the upper portion of the contact element having at least one pair of resilient fingers arranged to engage opposite sides of a connecting lug under pressure is solder-free.

A contact mounting implement is also provided in accordance with the invention for carrying out the method described above. The contact mounting implement comprises at least one contact element and at least one rod member made of non-solderable material and having a shape and dimensions comparable to the shape and dimensions of a lug to be inserted into the contact.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the accompanying drawings showing preferred embodiments of the lugreceiving and supporting contact structure made in accordance with the invention. In the figures; FIGURE 1 is a partial vertical cross-section illustrating a lug-receiving and supporting contact structure in accordance with the invention, the contact being mounted in a transverse hole of a printed circuit board; FIGURE 2 is a side elevational view of the contact element of FIGURE 1; FIGURE 3 is a partial side elevational view of an electronic component of the type to be inserted into the contact element of FIGURES 1 and 2; FIGURE 4 is a view similar to that of FIGURE 1, showing the contact element after the introduction of a non-solderable rod;; FIGURE 5 shows the further step of depositing solder around the lower bight portion of the contact element and metallized region of the printed circuit board in which the contact element is mounted; FIGURE 6 shows the completed lug-receiving and supporting structure after removal of the rod and introduction of a connecting lug of a circuit component; and FIGURE 7 shows diagrammatically a contact mounting implement used for inserting a plurality of contact elements in a printed circuit board simultaneously.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIGURES 1 and 2, the support structure for accomqdating a removable electronic component comprises a contact element 1 inserted in a transverse hole 30 in a printed circuit board 3, the latter item being represented in cross-section and showing a metallized region 32 on its underside.

Contact element 1 has a generally U-shaped lower bight portion 4 and is preferably formed by folding a stamped metal strip of resilient material.

In its formed configuration, the contact element 1 has a pair of substantially parallel lateral arms 5 and 6 widening to a widened upper portion 7 and 8 which has a width approximately three times that of lateral arms 5 and 6, as can best be seen in FIGURE 2. Each widened upper portion 7 and 8 is slit in two places with parallel lines aligned with the longitudinal axis of the contact element 1. The slits 12 define a pair of central fingers 10, 10' and a lateral pair of fingers 9, 9' and 11, 11' on either side of central finger pair 10, 10'.

The central fingers 10, 10' are longer than fingers 9, 9' and 11, 11' and extend substantially as a continuation of lateral arms 5 and 6 above the printed circuit board. The tips of fingers of 10, 10' are bent slightly inwardly and then diverge outwardly at their extreme upper ends, and the narrowest dimension between the free ends of fingers 10, 10' is approximately the same as the distance between inner wall surfaces lateral arms 5 and 6. This is to insure that a contact lug of an electronic component will be reliably guided between fingers 10, 10' and into the space between lateral arms 5 and 6.

The lateral pair of fingers 9, 9' and 11, 11' are arranged respectively on either side of the pair of central fingers 10, 10' and are bent outwardly just above the printed circuit board and then inwardly to touch each other adjacent the tips which separate again at their extreme free ends. The lateral fingers 9, 9' and 11, 11' have the approximate shape of S's and are arranged with back-to-back symmetry relative to a plane passing through the longitudinal axis of the contact element I and parallel to the lateral arms 5 and 6.

A typical electronic component of the type represented in FIGURE 3 has a connecting lug 20 of a thickness approximately equal to the minimum spacing between the tips of central fingers 10, 10' so as to assure an effective guiding of lug 20 upon its introduction into the contact structure.

The minimum spacing for lateral fingers 9, 9' and 11, 11' is shown to be zero in the example illustrated by FIGURE 1, and must always be less than the thickness of the connecting lug 20 to insure good electrical contact therewith. In the fully seated position of lug 20, the primary electrical engagement between contact and lug is at each side of the widened upper portion of the lug 20 shown in the shaded area 21 in FIGURE 3.

With reference to FIGURE 3, the component connecting lug 20 has a hip portion 22 widening to a width L which corresponds to the widened upper portion 7 and 8 of contact element 1. At the lower end, or free end, of component lug 20, a contact leg 23 has a width I which corresponds to the width of the lower portion of lateral arms 5 and 6 of contact element 1.

Contact element 1 is preferably made by stamping and folding an appropriately configured metallic sheet having good qualities of resiliency and solderability, the latter quality being necessary for being securely connected to metal layer 32 on the printed circuit board 31.

The following description referring to FIGURES 4-6 will aid in understanding the method of mounting a lug-receiving and supporting contact in a transverse hole in a printed circuit board. In a first step, illustrated by FIGURE 4, the contact element 1 is inserted in a transverse hole 30 of a printed circuit board 31. The hole opens at the lower face of the printed circuit board and is surrounded by a metallized layer region 32. After the contact element 1 is in place, a rod 33 of a material that is non-solderable is introduced in the central passageway defined conjointly by the lateral edges of transverse hole 30 of the printed circuit board 31 and the fingers of the contact element 1.

Preferably, the non-solderable material of rod 33 is selected from aluminium, stainless steel, polyamide, epoxy glass, or titanium. The shape and dimensions of the rod are preferably similar to those of the lower portion of the connecting lug 20 shown in FIGURE 3, in order that the lug 20 can thereafter be readily introduced into the contact structure after the rod 33 has been extracted. In order to take into consideration the tolerances of fabricating a component lug 20, the dimensions of rod 33 should be at least equal to or greater than the dimensions of the lower portion 23 of the connecting lug 20, so that, after the rod 33 is extracted, introduction of the component lug 20 can be affected without obstruction.

As FIGURE 5 illustrates, with rod 33 in place, a quantity of solder is deposited about the bight portion 4 of the contact element 1, the solder adhering to the external surfaces of the bight portion 4 and metallized layer 32 surrounding hole 30.

FIGURE 5 further illustrates that, since rod 33 may not fill the entire inner volume of the contact element 1, a slight flow of solder will take place beneath rod 33 and fill the tip of the inner surface of bight portion 4.

The completed connection of contact element 1 to the metal layer 32 of printed circuit board 31 shown in FIGURE 5 can be effected by means of standard lead-tin solder depositing techniques, i.e.

either manually or automatically by processing the board in a "solder wave" process. The solder deposit 34 having the shape of a meniscus, connects directly the metallized layer 32 with the lateral arms 5 and 6 of the lower portion of contact element 1. The same solder deposit 34 surrounds the rod 33 without molecularly engaging it, which permits, after complete solidification of the solder, withdrawing of the rod without difficulty.

After removal of rod 33, an imprint remains in the solder deposit being in the shape of rod 33.

The solder deposit 34 thus electrically and mechanically connects the contact element 1 with the metallized layer 32 of the printed circuit board 31 and constitutes, at least partially, a closed sheath into which can be introduced the free end of a connecting lug 20 of an electronic component (see FIGURE 6).

Due to their elasticity, the lateral finger pairs 9 and 11 assure a contact pressure sufficient for mechanically holding and electrically connecting component lug 20 at the contact points 21 (FIGURE 3).

According to an alternate embodiment of the method according to the invention, rod 33 can first be introduced into the longitudinal passageway 2 of a contact element 1, and subsequently the thus formed combination introduced as a whole into the hole of the printed circuit board. In such a case, it is advisable to affix the contact to be inserted on the end of the rod, and this can be accomplished by means of an adhesive which is not affected by an increase in termperature caused by performing the step of soldering the contact element 1 to the metal layer 32.For example, an anaerobic adhesive can be used, and due to the extremely small dimensions and mass of the contact elements, such adhesive will prevent the contact element and rod from becoming loosened from one another before and after introduction of the rod into the contact element, and yet at the same time will assure easy withdrawal of the rod after the soldering operation. A normal cleaning of the printed circuit board after soldering will eliminate any trace of adhesive left after the rod is removed.

The utilization of an adhesive that is not sensitive to an increase in temperature during the soldering operation permits realization of a contact mounting implement which can be beneficially used to mount a plurality of contact elements in a corresponding plurality of holes in a printed circuit board, all simultaneously. A particular embodiment of such a mounting implement is shown in FIGURE 7 in which a double legged rod 40 has depending rod legs 41 and 42 of non-solderable material. In FIGURE 7,.

an example is shown of the use of an anaerobic adhesive holding two contact elements 1 to be introduced into two holes of a printed circuit board the spacing of which corresponds exactly to the spacing between rods 41 and 42. Clearly, it is possible to construct a mounting implement comprising a plurality of parallel rods made of a non-solderable material, and these rods can be formed from a single piece or attached to a common body with the rods arranged according to a predetermined spacial pattern. The pattern may correspond, for example, to the pattern of the lugs of a particular electronic component, each of the rods having a contact element affixed thereto for introducing into respective holes of a printed circuit board, thereby locating and holding in place, while the soldering operation is performed, a plurality of contact elements.

From the foregoing, it can be readily realized that the invention can have many variations and modifications which will be evident for the expert in the field of art involved. Accordingly, it is to be understood that the invention is not to be limited to the specific embodiments and examples described herein, but is to be limited only by the appended

Claims

claims. CLAIMS

1. A method of mounting a lug-receiving and supporting contact in a transverse hole in a printed circuit board having a metallized region on one side thereof and surrounding said hole, comprising the steps of: providing a generally U-shaped lugreceiving contact element the arms of which open toward a lug-receiving end, and the bight portion of which defines a terminal end for said contact element; inserting said terminal end into said hole from the side of board opposite said metallized region until it emerges beyond said metallized region: inserting a non-solderable rod into said lug-receiving end of said contact element to occupy the space between said contact arms; forming a solder deposit about said terminal end and about the portion of said non-solderable rod exposed at the lateral sides of said terminal end; and removing said non-solderabie rod.

2. The method as claimed in Claim 1, wherein said rod is selected to have the shape and dimensions similar to that of a lug to be inserted in said contact.

3. The method as claimed in Claim 1, including, before said step of inserting said terminal end into said hole, the step of affixing said contact to said rod with a thermofusible adhesive which is fusible during said solder forming step to release said contact from said rod.

4. The method as claimed in Claim 1, wherein: said contact is provided at its lug-receiving end with a plurality of extended contact finger pairs, at least one of said finger pairs acting as a guide for facilitating insertion of said lug; and said step of inserting said non-solderable rod includes inserting said rod between the fingers of said one finger pair to avoid deforming the fingers of the other finger pairs.

5. The method as claimed in Claim 3, wherein: said providing step includes providing a plurality of said contacts; said steps of inserting said terminal end and inserting said rod comprises affixing one of said contacts to each of a plurality of connected rod members, and subsequently inserting all of said contacts into respective holes in said printed circuit board simultaneously; said forming step includes forming a solder deposit about each terminal end and about a portion of each of said rod members exposed at the sides of each terminal end; and said removing step includes removing said connected rod members simultaneously.

6. A lug-receiving and supporting contact structure comprising: and insulative plate member having a transverse hole therein and a metallized region on one side thereof surrounding said hole; a generally U-shaped lug-receiving contact element in said hole, the bight portion of said U-shaped contact element extending beyond said metallized region; and a deposit of solder covering the exterior surface and side edges of said bight portion extending beyond said metallized region surrounding said hole, leaving substantially the entire inner surface of said bight portion solderfree.

7. The contact structure as claimed in Claim 6, wherein: said contact element is formed from a folded strip of resilient metal, and the arms of said contact element adjacent said bight portion are open at both sides thereof prior to depositing of said solder and at least partially closed by said solder deposit to define a tubular sleeve comprised of the inner surface of said contact element and the portion of said solder deposit closing said open sides of said contact element.

8. The contact structure as claimed in Claim 7, wherein said tubular sleeve is shaped and dimensioned to receive a lug of complementary shape and dimension.

9. The contact structure as claimed in Claim 7, wherein the free ends of said U-shaped contact element comprise widened active contact parts continuous with said arms and slit parallel to the longitudinal axis of said contact element to form three resilient finger pairs, the fingers of the central finger pair having a width approximately the same as said arms adjacent said bight portion and separated a distance corresponding to the thickness of a lug to be inserted into said contact element, the fingers of the finger pairs on either side of said central pair having a spacing between fingers of each pair less than the thickness of a lug to be inserted into said contact structure.

10. The contact structure as claimed in Claim 9, wherein said central finger pair is longer than said lateral finger pairs to act as a guide for facilitating insertion of said lug.

11. The contact structure as claimed in Claim 9, wherein the free ends of said contact element are shaped to protrude outwardly above the upper surface of said plate member, and then curve inwardly to touch each other, and then curve outwardly at their tips.

1 2. A contact mounting implement for carrying out the method of Claim 1, comprising at least one contact element and at least one rod member made of non-solderable material and having a shape and dimensions comparable to the shape and dimensions of a lug to be inserted into said contact.

1 3. The contact mounting implement as claimed in Claim 12, wherein said contact element is fixed to said rod member with a thermofusible adhesive.

14. The contact mounting implement as claimed in Claim 13, wherein said rod member comprises a plurality of rod members arranged in a predetermined spacial pattern so as to permit simultaneous positioning and inserting of a plurality of lugs into said board.

15. A method for removably mounting an electronic component having at least one connecting lug on a printed circuit board provided with at least one transverse hole joining a face thereof adjacent to said electronic component to the metalized barrier of the opposite face, wherein a contact element having a receptacle for retaining said connecting lug and providing electric contact therewith is introduced into said transverse hole, the lower end of said contact element projecting from said metalized area on the opposite side; a non-solderable rod is engaged into the receptacle of said contact element and fixed, prior to insertion into said tranverse hole, to said contact element by means of a theremofusable adhesive, said rod having substantially the shape and at least the size of the end of said connecting lug; the lower end of said contact element is soldered to said metalized area and said adhesive is fused to free said rod; and said rod is then withdrawn from the receptacle of said contact element.

1 6. A method as set forth in claim 1 5, wherein said rod is non-solderable with soft solder, and said contact element is tin/lead soldered to said metalized area.

1 7. A contact element for introducing into a transverse hole in a board member, said contact element being fabricated of a folded metal strip having an enlarged upper end and a lower folded end narrow enough to be introduced into said board member, said enlarged upper end having two resilient free wings provided for retaining a connecting lug and providing an electric contact with said connecting lug.

18. The contact element as set forth in claim 17, wherein each free wing of said contact element comprises an enlarged upper end parallel to the longitudinal axis of said contact element for providing three branches in such a way as to constitute three pairs of branches.

19. The contact element as set forth in claim 18, wherein the width of the center pair of branches is substantially the same as the lower end of said contact element.

20. The contact element as set forth in claim 1 8, or 19 wherein the opposed faces of the branches of each lateral pair of branches abut each other prior to insertion of said connecting lug.

21. The contact element as set forth in claim 18, 19 or 20, wherein the width between the opposed faces of said center pair of branches is substantially equal to the thickness of said connecting lug.

22. The contact element as set forth in claim 18, 1 9, 20, or 21 wherein the branches of each pair of branches have generally the shape of two back-to-back S's, the lower end of each S being integral with the lower end of said contact element, and the convex sides of the upper loops facing each other and being arranged for resiliently abutting on the opposed faces of said connecting lug.