FR2472903A1 - Mounting parallelepiped component on PCB - by using two U=shaped plate metal supports, one leg having horizontal component support foot and other solder indents - Google Patents

Abstract

A parallelepiped shaped component such as a capacitor (10) is mounted on a printed circuit board (5) by two mounting pieces (2) of U-shaped channel metal, one leg (21) being higher than the other (26). The higher leg has a centre portion (25) pressed out and bent horizontal to serve as a support for the capacitor, spacing it above the board. The capacitor is soldered on the two centre portions of the pieces, the rounded bottom portions of which serve as feet and are located abutting solder ribs (55) on connection tracks (51) on the board. The solder ribs are heated to cause the solder to flow onto the presoldered pieces and provide an electrical soldered joint. The lower edge walls of the pieces have indents into which solder flows to provide additional mechanical securing of the pieces on the board.

Description

Attachment part of a component on a substrate and method of attachment
The present invention relates to the mounting of a component
on a substrate.

The component has a parallelepiped shape. This is for example
a ceramic dielectric capacitor. The surfaces of two
small opposite faces of the capacitor are covered with solder,
tinned or not, forming its two terminals.

The substrate has the form of a wafer and consists of
a dielectric material. It’s for example a ceramic plate,
vitrified or not, carrying conductive tracks which must
be connected the component.

The simplest method of fixing the component consists
to solder the terminals of the component directly to the conductive tracks
to which it is connected, forming weld fillets. The
temperature coefficients of the various materials concerned (composition
health, substrate and welding) are not identical, constraints
appear and faults may occur during welding
and over time.

One method of avoiding this drawback is to
use a capacitor with two attached conductive tapes
on either side of the capacitor and connected to its respective terminals
and connect the ends of the ribbons respectively to the
metal tracks by welding. A deformable fixing is thus obtained
reducing stresses.
other disadvantages ~ while capacitors of this type are used in assemblies
which must be defined in a frequency range up to
or even exceed 1 GHz, the connections between the capacitor and the
metal tracks have poor resistance and inductance
defined,
- the solder can go up along the tape and the solder and then
stiffen the connection and modify the inductors and capacities
parasites,
- inspection of the condition of the lower surface of the ribbons and the
capacitor1 under which the solder may have been inserted, is impossible
after soldering and possible cleaning of the circuit
may remain imperfect.

 With such a fixation, the visual control is therefore complex and the reproducibility of the electrical characteristics is therefore uncertain.

Another method of fixing a component to a substrate is obtained by interposing I-beams between the terminals of the capacitor (or component) and the tracks respectively. This fixing by means of I-beams makes it possible to control the state of cleanliness of the circuit, to obtain better defined and more easily reproducible electrical characteristics, to eliminate the constraints because it defines a deformable parallelogram. However, the mechanical connection made is fragile and can jeopardize the electrical connection obtained.

 The object of the present invention is to provide a fixing between a component and a substrate by interposing fixing pieces between the terminals of the component and the tracks of the substrate avoiding the above drawbacks.

The subject of the present invention is therefore a part for fixing a component to a substrate, intended to ensure the connection between one of the terminals of the component and one of the conductive tracks of the substrate, characterized in that it has the general shape of a flat hook clip having two legs of different height joined by a rounding, the largest of the legs being divided into two parts, one called the upper part intended to be welded to said terminal of the component and the other adjoining to the rounding intended to ensure a spacing between the component and the substrate, the rounding ensuring the positioning of said part relative to the end of the track and the small leg intended to be welded to said track having at least one imprint in relief towards the interior of the rounding intended to ensure, during the welding of the small jamb on the track, the blocking of the part on the substrate.

According to another characteristic, said fixing part has a flap on its large leg, separating the two parts defined over its height, forming with the large leg an external positioning bracket for the component on the connecting part.

The present invention also relates to a method of fixing a component to a substrate by interposing two fixing parts defined above between two terminals of the component.

and two tracks of the substrate between which the component is to be connected, characterized in that it consists in soldering the terminals and the upper parts of said fasteners respectively, in carrying out an oontrol of the component equipped with said fasteners, in positioning the component equipped with said parts and controlled on the substrate so that the weld beads with which said tracks come tangent to the outside of the rounding of the fixing parts, on the side of the small jambs of these parts respectively, and to cause by heating the formation of weld fillets on the outer surface of the small jamb of each of the fixing parts.

The characteristics and advantages of the present invention will emerge from the description of an exemplary embodiment, given with reference to the attached drawing. In this drawing - FIG. 1 is a partial perspective view of a component equipped with a fixing piece according to the invention, - FIG. 2 represents a series of fixing pieces presented in a strip, - FIG. 3 is a partial sectional view of a component equipped with a fixing part, - Figure 4 shows a substrate carrying a first component and receiving a second component, - Figure 5 is a section illustrating the connection of the fixing part to a track of a substrate.

In all these figures, the various elements are shown on a much enlarged scale, the chosen scale being different from one figure to another according to the particularities highlighted.

 In FIG. 1, a component 1 is shown, for example a capacitor, carrying a fixing part 2 intended to ensure the fixing of the component on a substrate. The fixing part 2 is mounted on one of the small lateral faces of the component, carrying a silver-palladium solder forming a terminal 3 of the component. This solder is covered by a layer of tin-lead alloy, with a melting point close to 3000C. The other small side face of the component, not shown, is identical to it and forms the second terminal of the component, it also carries a fixing part identical to part 2.

The fixing part 2 is made of "fine tinned" copper, it has the general shape of a flat hook clip having two legs 21 and 22 of different height joined by a rounded 23. The largest of these legs, here the leg 21 , has an axial cut 24 open on its edge opposite the rounding 23 and a flap 25 forming with the leg 21, on the inside of the fixing piece, a square. This flap 25 is here constituted by all or part of the portion of the leg, at the location of the cutout 24, this portion being folded at right angles to the outside of the part 2. The flap is substantially halfway up the jamb 21.

The small jamb 22 carries, near its edge opposite to the rounded 23, two imprints 26 and 27, from stamping, in relief towards the inside of the rounded. These two imprints are here open on the edge opposite to the rounding 23 and are on either side of a median portion of this leg.

In the fixing part 2, the height of the large leg 21 is provided on the one hand to allow its attachment to the component and on the other hand to allow the maintenance of a spacing between the component and the substrate, as well as will be seen below. The flap 25 divides the leg 21 into two parts: the upper part is fixed to the component which comes to bear on the flap, the lower part defines the component-substrate spacing
The connection piece 2 is fixed to the component 1, after positioning the component on the flap 25, by pressing the upper part of the leg 21 and the solder 3 against each other and applying a temperature to them , of the order of 3500C, sufficient to ensure the melting of the tin-lead alloy which covers the two parts to be welded.

 The component provided with two parts 2, respectively on its two terminals, is then checked, this before being placed on the substrate, a check carried out at this stage, that is to say before placing the component on the substrate. , being particularly advantageous from a practical point of view.

 With reference to FIG. 2, in which three fastening parts 2 are illustrated, it can be seen that the fastening parts are produced from a strip 4 and presented under a strip. This tinned strip, initially rectangular, is cut along one of its large edges to define on this edge recessed portions 40 between the fixing parts which will be formed. The uncut parts of this large edge are folded and cut appropriately to form the fasteners made from the same initial strip and remaining integral with this strip. Holes 41, in line with the recessed portions 40 on the large edge considered of the initial strip, are formed in the strip 4. These circular holes 41 here allow the strip to be driven and the fixing pieces 2 to be positioned for forming impressions 26 and 27 by stamping.

In addition, for each part 2, the part of the strip separated from the large leg 21 to form the flap 25 carries a precut 28, shown diagrammatically by dotted lines, at a short distance from the large leg 21.

This pre-cut 28 allows easy separation of each fastening part 2 from the strip 4.

 The mounting of these fastening parts on components can be done while the parts 2 remain integral with the strip 4 which facilitates their handling or while these parts are detached from the strip.

 In FIG. 3, a fixing part 2 is illustrated, which is still integral with the strip 4 mounted on the component 1. We can see the component 1 bearing thereon on the flap 25 and on its extension beyond the precut 28. The holding the part 2 on the component is ensured at the solder 3 and the upper part of the leg 21 which are welded. There is also indicated the distance d between the flap 25 and the rounding 23 of the part 2, it is this distance d which will fix the distance between the component and the substrate on which it is to be mounted.

 The part 2 being fixed on the component 1, it is then separated from the strip 4 by simple folding of the strip 4, according to the arrow f.

 In Figure 4, there is illustrated a substrate 5, or circuit board, receiving two components. These two components are referenced 10 and 11 respectively, they are each equipped with two fixing pieces 2 constituting for each of them a device for fixing to the substrate 5. The component 10 is considered here connected to two conductive tracks 50 and 51 of the component, the component 11 is simply ready to be connected to two other conductive tracks 52 and 53 of the substrate.

 It can be seen, with reference to this FIG. 4, that each fastening piece 2 has been given a length L slightly greater than the width l of the terminal part of the track to which it is to be connected, this facilitating good positioning of the fixing piece on the track, and making it possible to prevent the weld after fusion from reaching the side of the leg 21 of said fixing piece.

The conductive tracks 52 and 53 to which the component 11 must be connected are provided with weld beads of tin-lead alloy 54 with a low melting point, the distance D between these tracks is such that the surface of the weld beads comes to tangent l exterior of the rounds of the two fixing parts 2 mounted on the component 11. This gives lateral self-centering of the component. The application of a heating, localized or not, to a temperature of the order of 2300C melts the tin-lead solder beads with low melting point deposited on the tracks and causes the formation of a fillet on the part outside of the rounding and small jamb of each of the two fixing pieces 2. These leaves appear for the component 10 considered mounted on the substrate and are referenced by 55.

The spacing d obtained between the component and the substrate after the connection has also been made appear, opposite the component 10.

The connection of the fastening pieces 2 on the metal tracks, for example, of the piece 2 on the track 51, appears more clearly in the sectional view given in FIG. 5 and made at the level of one of the imprints, here l footprint 26 of the small jamb 22.

We see the leave 55 formed by the weld which "wets" the outer part of the round 23 and the small leg 22 and penetrate into the cavity 26 while ensuring a blocking of the fixing piece on the substrate. The external surface of part 2, on the component side, remains free of any trace of welding.

By means of two fixing parts 2, a deformable fixing device of the component is therefore produced on the substrate, thus avoiding the mechanical stresses and the defects which may result therefrom.

The connection obtained does not call into question the intrinsic reliability of the component, once the component equipped with its two fixing parts and having been checked, no new thermal shock is applied to the component. In addition, this connection makes it possible to obtain a faithful reproduction of the electrical parameters, this due to a rigorous positioning achieved by the self-centering of the roundings between the weld beads. The welds produced are easy to control, a simple visual examination makes it possible to assess the quality of the weld produced by observing the rate of formation of the leave and the appearance of the leave made. The mechanical retention of the component on the substrate, ensured by the welding of the two concerned faces of the component respectively on the fixing pieces and by the weld fillets with blocking in the cavities, is of good quality and makes it possible to preserve the qualities of the connection electric by welding.

Claims (6)

 1 / Component fixing part on a substrate, intended to ensure  the connection between one of the component's terminals and one of the conductive tracks  trices of the substrate, characterized in that it has the form  general of a flat hook clip having two legs different joined by a rounding, the largest of the legs being divided into two parts, one called the upper part intended to be welded  to said component terminal and the other adjoining the rounding intended to ensure a spacing between the component and the substrate, the rounding  ensuring the positioning of said part relative to the end of the track and the small leg intended to be welded to said track  having at least one raised imprint towards the inside of the rounding intended to ensure when welding the small jamb on the track blocking of the part on the substrate.  2 / fastener according to claim 1, characterized in  that it has a flap secured to the large jamb and separating the two parts defined there according to its height, forming with  the large jamb a square towards the outside of the room for the component positioning. 3 / fastener according to claim 2, characterized in that  that it has a cut in the upper part of the large jamb, to the right of the flap. 4 / Method for fixing a component on a substrate by interposition  of two fixing parts according to one of claims 1 to 3 between two component terminals and two substrate tracks between which the component is to be connected, characterized in that it consists of  solder the terminals and the upper parts of said fixing parts  respectively, to carry out a control of the component equipped with said  fixing parts, to position the component equipped with said parts  and checked on the substrate so that weld beads  which are provided with said tracks tangent outside of  rounded fasteners, on the side of the small jambs of these parts respectively, and to cause by heating the formation  weld leave on the outside surface of the small jamb each of the fasteners.  5 / A fixing method according to claim 4, characterized in that the terminals of the component and at least the upper part of the large leg of each fixing part being tinned, the welding of the upper part of the fixing parts on the terminals of the component is carried out by pressing the terminal and the upper part of the part concerned against each other and by causing the melting of the tin-lead alloy which covers them by heating. 6 / A fixing method according to one of claims 4 and 5, characterized in that it consists initially in preparing the substrate by giving each of the tracks between which the component must be connected a width slightly less than the length of the rounding of each of the fixing parts.