Barrier for Preventing SMT Components from Drifting

Abstract

The invention relates to a method for soldering an SMD component (1) to a circuit carrier (2) in a positionally stable manner, having the following steps: a) providing a circuit carrier (2) comprising at least one printed circuit board contact surface (2a), which is coated with a soldering paste (3) and which is designed to electrically, thermally and/or mechanically contact the SMD component (1) to be connected, wherein a number of filled vias (6), which cannot be coated with molten solder, pass through the circuit carrier (2) at least in the region of the printed circuit board contact surface (2a), b) applying at least one adhesive point (4a, 4b, 4c, 4d, 4e) onto the circuit carrier (2) such that the adhesive point (4a, 4b, 4c, 4d, 4e) delimits the printed circuit board contact surface (2a) coated with soldering paste (3) on at least one side of an edge point (R.sub.a, R.sub.b) paired with the soldering paste (3), c) placing an SMD component (1), which comprises at least one component contact surface (1a), on the printed circuit board contact surface (2a) coated with soldering paste (3) such that the at least one component contact surface (1a) electrically, thermally and/or mechanically contacts the printed circuit board contact surface (2a) via the soldering paste (3) lying therebetween, said placement being carried out and the position of said at least one adhesive point (4a, 4b, 4c, 4d, 4e) being selected in step b) such that the SMD component (1) rests on the soldering paste (3) without contacting the at least one adhesive point (4a, 4b, 4c, 4d, 4e), d) waiting for a specifiable duration t until a curing process of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is complete, and e) heating, melting and subsequently cooling the soldering paste (3) in order to produce an electric, thermal and/or a mechanical connection between the at least one component contact surface (1a) of the SMD component (1) and the at least one printed circuit board contact surface (2a) of the circuit carrier (2), wherein a barrier (5) is formed using the at least one adhesive point (4a, 4b, 4c, 4d, 4e) such that, first, the SMD component is allowed to vertically sink in the molten state of the soldering paste (3) and, second, the SMD component is mechanically restricted from drifting horizontally on the molten soldering paste (3) in the direction of the barrier (5) by means of the barrier (5).

Claims

1. A method for soldering an SMD component (1) to a circuit carrier (2) in a positionally stable manner, comprising the following steps: a) providing a circuit carrier (2) comprising at least one printed circuit board contact surface (2a) that is coated with soldering paste (3) and designed for electrically, thermally and/or mechanically contacting the SMD component (1) to be connected, wherein a number of filled vias (6), which cannot be coated with molten soldering material, extend through the circuit carrier (2) at least in the region of the printed circuit board contact surface (2a); b) applying at least one adhesive point (4a, 4b, 4c, 4d, 4e) onto the circuit carrier (2) in such a way that this adhesive point (4a, 4b, 4c, 4d, 4e) delimits the printed circuit board contact surface (2a) coated with soldering paste (3) at an edge point (R.sub.a, R.sub.b) assigned to at least one side of the soldering paste (3); c) placing an SMD component (1) comprising at least one component contact surface (la) on the printed circuit board contact surface (2a) coated with soldering paste (3) in such a way that the at least one component contact surface (la) electrically, thermally and/or mechanically contacts the printed circuit board contact surface (2a) via the soldering paste (3) lying therebetween, wherein said placement is carried out in such a way and the position of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) in step b) is chosen in such a way that the SMD component (1) rests on the soldering paste (3) without contacting the at least one adhesive point (4a, 4b, 4c, 4d, 4e); d) waiting for a specifiable duration t until a curing process of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is complete; and e) heating, melting and subsequently cooling the soldering paste (3) in order to produce an electrical, thermal and/or mechanical connection between the at least one component contact surface (la) of the SMD component (1) and the at least one printed circuit board contact surface (2a) of the circuit carrier (2), wherein a barrier (5) is formed with the aid of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) in such a way that, first, the SMD component is allowed to vertically sink in the molten state of the soldering paste (3) and, second, the SMD component is mechanically restricted from horizontally drifting off in the direction of the barrier (5) on the molten soldering paste (3) by means of the barrier (5).

2. The method according to claim 1, wherein the printed circuit board contact surface (2a), which is coated with soldering paste (3) in step a), is surrounded by a solder resist layer (8), and wherein the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is arranged on the solder resist layer (8) and/or on a section of the printed circuit board contact surface (2a) that is not coated with soldering paste (3).

3. The method according to claim 1, wherein the height (h.sub.1) of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) amounts to at least 40% of the height (h.sub.2) of a soldering paste deposit (3a) formed by the soldering paste (3) in the non-molten state, and wherein the barrier is exclusively formed by the at least one adhesive point (4a, 4b, 4c, 4d, 4e) itself.

4. The method according to claim 1, wherein at least one adhesive point (4a, 4b, 4c, 4d, 4e) is realized in the form of a spherical calotte.

5. The method according to claim 1, wherein at least a first adhesive point (4a, 4b, 4c, 4d, 4e) is expanded linearly so as to form a linear barrier (5).

6. The method according to claim 5, wherein at least one second adhesive point is provided, and wherein the second adhesive point is designed linearly such that an essentially L-shaped or U-shaped contour, which at least partially encloses the SMD component (1), is formed together with the first adhesive point.

7. The method according to claim 1, wherein the height (h.sub.1) of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) amounts to at least 50 micrometer.

8. The method according to claim 1, wherein at least one delimiting body (7) is placed on the at least one adhesive point (4a) after step b) and prior to step d), and wherein the barrier (5) is formed with the aid of the delimiting body (7).

9. The method according to claim 1, wherein the at least one adhesive point (4a, 4b, 4c, 4d, 4e) consists of hot-curing material and curing of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) in accordance with step d) takes place by increasing the temperature of the circuit carrier (2) together with the at least one adhesive point (4a, 4b, 4c, 4d, 4e), wherein this takes place, in the course of a reflow soldering process, and wherein the temperature required for the hot-curing process lies below the melting temperature of the soldering material.

10. The method according to claim 1, wherein the adhesive material is chosen in such a way that the volume of the adhesive decreases by no more than 10% during the curing process.

11. The method according to claim 1, wherein the adhesive material is realized in a hot-curing manner and chosen in such a way that it expands under the addition of heat during the curing process according to step d).

12. The method according to claim 1, wherein the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is applied by means of a dispenser and the SMD component (1) is placed by means of an automatic placement machine, wherein the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is in step b) positioned in such a way that it has at least a safety clearance (s) from the edge region of the nominal position of the SMD component (1), and wherein this safety clearance (s) is formed of the sum of the positioning tolerances of the dispenser and the automatic placement machine, the size tolerance of the at least one adhesive point (4a, 4b, 4c, 4d, 4e), as well as the component tolerance of the SMD component (1), and amounts to at least 50 micrometer.

13. The method according to claim 12, wherein the SMD component (1) has a rectangular footprint (1c) and the at least one adhesive point (4a, 4b, 4c, 4d, 4e) is positioned in such a way that the at least one adhesive point (4a, 4b, 4c, 4d, 4e) lies after the placement of the SMD component (1) in step b) in the immediate vicinity of one side of the rectangular footprint (1c) while maintaining the safety clearance(s).

14. The method according to claim 1, wherein the number of adhesive points (4a, 4b, 4c, 4d, 4e) is in step b) chosen in such a way that just one adhesive point (4a, 4b, 4c, 4d, 4e) is assigned to each side and/or corner of the SMD component (1).

15. A circuit carrier (1) manufactured with a method according to claim 1.

16. The method according to claim 3, wherein the height (h.sub.1) of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) amounts to at least 60% of the height (h.sub.2) of the soldering paste deposit (3a).

17. The method according to claim 3, wherein the height (h.sub.1) of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) amounts to at least 100% of the height (h.sub.2) of the soldering paste deposit (3a).

18. The method according to claim 6, wherein the at least one second adhesive point contacts the first adhesive point.

19. The method according to claim 7, wherein the height (h.sub.1) of the at least one adhesive point (4a, 4b, 4c, 4d, 4e) amounts to at least 100 micrometer.

Description

[0038] The invention is described in greater detail below with reference to an exemplary and nonrestrictive embodiment that is illustrated in the figures. In these figures,

[0039] FIG. 1a shows a schematic representation of a section of a circuit carrier with an SMD component to be fastened thereon in accordance with the prior art,

[0040] FIG. 1b shows a drifted-off fastened SMD component according to FIG. 1a,

[0041] FIG. 2a shows a sectional representation of an embodiment according to the invention in the non-soldered state,

[0042] FIG. 2b shows a sectional representation according to FIG. 2a in the soldered state,

[0043] FIG. 2c shows a detail of FIG. 2b,

[0044] FIG. 2d shows another detail of FIG. 2b, in which the SMD component impacts on a barrier and is thereby held in its position,

[0045] FIGS. 3a to 3d show different variations of adhesive point configurations according to the invention, and

[0046] FIGS. 4a to 4d show different variations of delimiting body configurations according to the invention.

[0047] In the following figures, identical characteristics are—if not indicated otherwise—identified by the same reference symbols.

[0048] FIG. 1a shows a schematic representation of a section of a circuit carrier 2 with an SMD component 1 to be fastened thereon in accordance with the prior art. According to FIG. 1b, the component 1 has drifted off on a not-shown solder deposit 3 during the soldering process and was permanently soldered in this drifted-off end position.

[0049] FIG. 2a shows a sectional representation of an embodiment according to the invention in the non-soldered state. This figure shows an arrangement on which the inventive method is carried out. The invention relates to a method for soldering an SMD component 1 to a circuit carrier 2 in a positionally stable manner and comprises the following steps a) to e) in the exemplary embodiment shown:

a) Providing a circuit carrier 2 comprising at least one printed circuit board contact surface 2a that is coated with soldering paste 3 and designed for electrically, thermally and/or mechanically contacting the SMD component 1 to be connected. A number of filled vias 6, which cannot be coated with molten soldering material, extend through the circuit carrier 2 at least in the region of the printed circuit board contact surface 2a. This number is basically variable and not limited to a certain value.
b) Applying—in this exemplary embodiment—two adhesive points 4a and 4b onto the circuit carrier 2 in such a way that these adhesive points 4a and 4b delimit the printed circuit board contact surface 2a coated with soldering paste 3 at respective edge points R.sub.a and R.sub.b, each of which is assigned to one side of the soldering paste 3. In this context, the term edge point refers to a point that is respectively assigned to one side of the soldering paste 3 or an overlying side of the SMD component 1. The term “delimiting” refers to a “restriction.” This does not mean that the edge point is contacted by the respective adhesive point 4a or 4b during the application. On the contrary—a minimum clearance in relation to the SMD component 1 is provided as described in greater detail below. The term “delimiting” refers to the restriction of a drift-off process of the SMD component 1 and the edge points, particularly Ra and Rb, respectively describe a point on exposed edges or projections of the component 1 that impacts on a barrier 5 or an adhesive point 4a or 4b, for example, during a drift-off process.
c) Placing an SMD component 1 comprising at least one component contact surface 1a on the printed circuit board contact surface 2a coated with soldering paste 3 in such a way that the at least one component contact surface 1a electrically, thermally and/or mechanically contacts the printed circuit board contact surface 2a via the soldering paste 3 lying therebetween. The placement is carried out in such a way and the position of the adhesive points 4a and 4b in step b) is chosen in such a way that the SMD component 1 rests on the soldering paste 3 without contacting the adhesive points 4a and 4b.
d) Waiting for a specifiable duration t, e.g. one minute, until a curing process of the adhesive points 4a and 4b is complete (more precisely, this process may take, for example, as long as 1-5 min depending on the temperature—in a typical reflow process with a ˜150° C. plateau phase at the beginning, this process will take approximately 90-120 s).
e) Heating, melting and subsequently cooling the soldering paste 3 in order to produce an electrical, thermal and/or mechanical connection between the at least one component contact surface 1a of the SMD component 1 and the at least one printed circuit board contact surface 2a of the circuit carrier 2. A barrier 5 is formed with the aid of the adhesive points 4a and 4b, which in FIG. 2b are illustrated in the already cured state, in such a way that, first, the SMD component is allowed to vertically sink in the molten state of the soldering paste 3 and, second, the SMD component is mechanically restricted from horizontally drifting off in the direction of the barrier 5 on the molten soldering paste 3 by means of the barrier 5. In the present example, the barrier 5 is jointly formed by the two adhesive points 4a and 4b.

[0050] FIG. 2c shows a detail of FIG. 2b. According to this figure, the now solidified soldering 5 material 3 has changed with respect to its distribution due to the influence of the via 6: since the via likewise lies in the edge region of the contacting of the SMD component 1 and the via cannot be coated with soldering material 3, the soldering material 3 has withdrawn to a region lying underneath the SMD component 1. Mechanical forces, which promote a drift-off of the component 1, are exerted upon the SMD component 1 due to does “withdrawal.” The drift-off does not always occur—although the component 1 did not remain in its position in the present example. In contrast, FIG. 2d shows a scenario, in which the component 1 impacts on the barrier 5 and is held in its position by this barrier.

[0051] FIGS. 2a and 2b show that the printed circuit board contact surface 2a, which is coated with soldering paste 3 in step a), is surrounded by a solder resist layer 8, wherein the two adhesive points 4a and 4b are arranged on the solder resist layer 8. However, the adhesive points do not necessarily have to be placed on the printed circuit board layer, but rather may also be located, for example, on the printed circuit board contact surface 2a of the printed circuit board.

[0052] The height h.sub.1 (see FIG. 2a) of the adhesive points 4a, 4b, 4c, 4d, 4e amounts to at least 40%, preferably at least 60%, particularly at least 100%, of the height h.sub.2 (see FIG. 2a) of a soldering paste deposit 3a formed by the soldering paste 3 in the non-molten state, wherein the barrier 5 is exclusively formed by the adhesive points 4a and 4b themselves.

[0053] FIGS. 2a and 2b show that the adhesive points 4a and 4b are realized in the form of spherical calottes.

[0054] FIGS. 3a to 3d show different variations of adhesive point configurations according to the invention. FIG. 3a shows the use of a single adhesive point 4a that is positioned on one side of the SMD component 1. FIG. 3b shows a variation, in which adhesive points 4a and 4b are respectively positioned on a corner of the SMD component 1. FIG. 3c shows a variation, in which another adhesive point 4c arranged on the side is provided in addition to the corner adhesive points 4a and 4b. FIG. 3d shows the use of five successively arranged adhesive points 4a, 4b, 4c, 4d, 4e, which are jointly expanded linearly in order to form a linear barrier 5 (“adhesive bead”). Numerous other configurations are basically also conceivable. It would be possible, for example, to provide at least one second adhesive point that preferably contacts 5 the first adhesive point, wherein the second adhesive point is designed linearly such that an essentially L-shaped or U-shaped contour, which at least partially encloses the SMD component 1, is formed together with the first adhesive point.

[0055] FIGS. 4a to 4c show different variations of delimiting body configurations according to the invention. According to these figures, at least one delimiting body 7 is placed on the at least one adhesive point 4a (which is not illustrated in the figures) after step b) and prior to step d). The barrier 5 is formed with the aid of the delimiting body 7. The delimiting body may be realized in a U-shaped (FIG. 4c) or L-shaped (FIG. 4b) manner or also have a straight shape (FIG. 4a). Multiple delimiting bodies 7 may also be used.

[0056] The adhesive points preferably consist of hot-curing material. The hot-curing temperature lies below the melting temperature of the soldering material.

[0057] FIGS. 3a to 4c show that the SMD component 1 respectively has a rectangular footprint 1c (see FIGS. 3a and 4a for reference symbols). According to FIG. 3a, the adhesive point 4a is positioned in such a way that it lies after the placement of the SMD component 1 in step b) in the immediate vicinity of one side of the rectangular footprint 1c while maintaining the safety clearance.

[0058] The invention is not limited to the embodiments shown, but rather defined by the entire scope of protection of the claims. Individual aspects of the invention or the embodiments can also be selected and combined with one another. Any reference symbols in the claims are exemplary and merely serve for the easier readability of the claims without restricting these claims.