Method for producing a reflow-soldered connection and printed circuit board arrangement

Abstract

The present invention relates to a method for producing a reflow-soldered connection on a printed circuit board arrangement, comprising the steps of applying a first solder deposit on a printed circuit board to produce a reflow-soldered connection, arranging a soldering auxiliary component on a wire end of a wire, positioning the wire end with the soldering component on the first solder deposit, and reflow-soldering the wire and the soldering auxiliary component to the printed circuit board in order to produce a reflow-soldered connection between the wire and the printed circuit board and between the soldering auxiliary component and the printed circuit board, wherein, during reflow-soldering, the soldering auxiliary component is movable at the wire end of the wire in order to enable tolerance compensation between the wire and the printed circuit board for a contact-proof reflow-soldered connection.

Description

[0001] R.416452

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for producing a reflow solder joint and printed circuit board arrangement

[0006] State of the art

[0007] The present invention relates to a method for producing a reflow solder joint on a printed circuit board assembly with a possibility for compensating for tolerances during the soldering process, as well as a printed circuit board assembly.

[0008] In power electronics, for example, surface-mount devices (SMDs) are fixed to printed circuit boards (PCBs) using the reflow soldering process. In this process, a solder deposit is applied to the PCB, the components to be mounted are placed on the solder deposit, and then heated in an oven. This creates an electrical connection between the components and the PCB. However, in power electronics, components with wire leads, such as transformers, chokes, or similar devices, also need to be fixed to the PCB. This presents a problem: the wire end of a wire to be fixed may have an irregular surface, bevels, or similar features resulting from a cutting process. This can lead to contact problems and an incomplete or non-existent solder joint during reflow soldering.Therefore, such components with wire connections are often fixed to the printed circuit board (PCB) using through-hole technology (THT). While this ensures reliable electrical contact, it requires THT technology in addition to reflow soldering to fully populate the PCB. Furthermore, there are applications where it is desirable to have one side of the PCB free of components and / or protruding wire ends from the THT mounting, umR.416452.

[0009] -2 -

[0010] in particular to attach a surface cooler to the free underside of the circuit board.

[0011] Disclosure of the invention

[0012] The inventive method for producing a reflow solder joint on a printed circuit board assembly between a wire and a printed circuit board has the significant advantage that wire tolerances can be compensated for, thus enabling the creation of a reliable solder joint between the wire and the printed circuit board. This allows, for example, the compensation of problems that can arise from an insufficient amount of solder on the printed circuit board and tolerances between the printed circuit board surface and the component pin or wire, which can lead to incomplete solder joints. Deformations of the printed circuit board during the soldering process can also be compensated for. The invention therefore provides a reflow solder joint of the highest quality for a wire.

[0013] This is achieved according to the invention by the method comprising the following steps: In one step, a first solder deposit is applied to a printed circuit board to produce the reflow solder joint.

[0014] In a further step, a soldering aid is arranged at the wire end that is to be fixed to the printed circuit board (PCB). The wire end with the soldering aid is then positioned on or at the first solder deposit. Finally, the wire and the soldering aid are reflow soldered to the PCB to form the reflow solder joint between the wire and the PCB, as well as between the soldering aid and the PCB. According to the invention, during reflow soldering, the soldering aid is movably arranged at the wire end to allow for tolerance compensation between the wire and the PCB. This mobility of the soldering aid minimizes the coplanarity of the contact surface to an absolute minimum, i.e., contact tolerance approaching zero. This is particularly advantageous for components with more than three contact points. R.416452

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[0016] The flexibility before and during reflow allows tolerances of the connection pins to be completely compensated for by the soldering aid component.

[0017] The soldering aid component also prevents excessive solder flow from the first solder deposit during the reflow soldering process. In particular, this prevents unwanted solder bridges to adjacent solder joints. Furthermore, the soldering aid component ensures that even if the wire end is angled, for example, due to a wire cutting process, it does not make insufficient contact with the circuit board. The soldering aid component ensures that a sufficient amount of solder is present at the wire end for reliable contact with the circuit board. Thus, according to the invention, wire ends whose end face is not perpendicular to the longitudinal direction of the wire can be reliably connected to the circuit board by means of reflow soldering. Furthermore, the geometry for SMD connections can be optimized, and reliable and rapid automated optical inspection can be enabled.

[0018] The dependent claims describe preferred embodiments of the invention.

[0019] Preferably, the soldering aid is already movably positioned at the wire end before the reflow soldering process. This allows for easy positioning of the soldering aid on the wire.

[0020] To prevent the soldering aid from being lost from the wire during the soldering process, the wire end is preferably bent at a predetermined angle. Preferably, the angle is greater than 45° and ideally lies between 45° and 90°. This ensures the soldering aid is securely held on the wire. Preferably, the wire end is bent back into its original position before soldering. Alternatively, the wire can be locally deformed by crimping.

[0021] Preferably, a second solder deposit is arranged on the soldering aid component or on the wire in the area where the soldering aid component is located. The second solder deposit provides an additional quantity of solder during reflow soldering and can be used for R.416452.

[0022] - 4 -

[0023] Further improve the connection between the soldering aid component and the circuit board, as well as between the wire and the circuit board.

[0024] Preferably, the second solder deposit does not establish a connection between the soldering aid component and the wire in the initial state, but is arranged either on the soldering aid component or on the wire without a fixed connection between the soldering aid component and the wire, so that the soldering aid component is movably arranged on the wire before reflow soldering despite the second solder deposit.

[0025] Alternatively, the second solder deposit is designed such that the soldering aid component is fixed to the wire end by means of the second solder deposit before reflow soldering. During reflow soldering, the second solder deposit then melts, so that the soldering aid component is able to move relative to the wire during reflow soldering.

[0026] If a second solder deposit is present, the material of the first solder deposit is preferably the same as the material of the second. This ensures that the melting point of the first and second solder deposits is the same. Alternatively, the first solder deposit has a first melting point that is higher than the second melting point of the second solder deposit. This means that during a temperature increase during reflow soldering, the second solder deposit melts before the first. This ensures the mobility of the soldering aid, if it is fixed to the wire by means of the second solder deposit, before the first solder deposit melts. Regardless of whether the second solder deposit fixes the soldering aid to the wire or not, the earlier melting of the second solder deposit results in the soldering aid being pre-aligned with the wire, and the solder from the second solder deposit flows towards the first solder deposit due to gravity, increasing the amount of solder present there.

[0027] The soldering aid component particularly preferably has a fully enclosed area as its base body through which the wire is guided. The fully enclosed area of ​​the soldering aid can be ring-shaped, so that the base body of the soldering aid component is designed as a hollow cylinder, or the base body is designed as a band encircling the wire. This allows for a gap between the band ends on the soldering aid component, or for the wire to be enclosed within it.

[0028] -5 -

[0029] The encircling band is arranged crosswise at the open point to enclose the wire.

[0030] Particularly preferred are protruding elements arranged on the base body of the soldering aid component to provide increased heat input to the soldering aid component during reflow soldering. The protruding elements can be flag-like elements that extend at an angle from the soldering aid component.

[0031] The soldering aid component is preferably made of the same material as the wire, in particular of an electrically conductive metal with good solderability.

[0032] Preferably, the wire end is left untreated, i.e., free from tinning or similar coatings. This eliminates a normally necessary manufacturing step during wire end preparation, namely tinning the wire end for reliable soldering. As a result, the manufacturing costs of the printed circuit board assembly can be significantly reduced.

[0033] It is also preferred that the underside of the circuit board be free of components.

[0034] In particular, no holes need to be provided in the circuit board for through-hole technology (THT) connections. This allows the circuit board to be supplied without holes, which also reduces manufacturing costs. The underside of the circuit board, which is thus free of components and / or holes, provides an excellent surface for attaching a cooling element. Preferably, the underside of the circuit board is also populated. Furthermore, the circuit board can be designed with any number of layers. Additionally, there is no need to define exclusion zones on the circuit board, which simplifies the circuit board layout.

[0035] Preferably, the wire diameter is greater than or equal to 1 mm, particularly 2 mm. Thus, the invention can be used especially with so-called thick wire. More preferably, the wire is a stranded wire produced by a plurality of wire strands with a smaller diameter than the final wire. Here, the present invention offers significant advantages, particularly when using the second solder deposit. R.416452

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[0037] during the safe creation of the soldered connection between the wire and the circuit board.

[0038] Furthermore, the present invention relates to a printed circuit board arrangement which is manufactured according to a method according to the invention.

[0039] The printed circuit board arrangement preferably comprises a printed circuit board, a solder joint between a wire and the printed circuit board and a soldering aid component, wherein the solder joint also provides a solder connection between the soldering aid component and the printed circuit board.

[0040] The soldering aid is particularly preferably a hollow cylinder or a hollow cylinder with an annular flange arranged at the free end of the hollow cylinder facing the circuit board, or a funnel-shaped element with an opening for receiving the wire, or a double-funnel-shaped element with an opening for receiving the wire, or a strip material formed into a loop to create an opening for receiving the wire. The soldering aid preferably has projecting areas, in particular flags or the like. A second solder deposit is more preferably arranged on the soldering aid and / or at the wire end.

[0041] Brief description of the drawings

[0042] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows:

[0043] Figure 1 shows a schematic, perspective view of a printed circuit board arrangement produced using a method according to the invention.

[0044] Figure 2 shows a schematic sectional view of the printed circuit board arrangement of Figure 1.

[0045] Figure 3 shows a perspective view of a wire and a soldering aid component of the printed circuit board arrangement of Figure 1, R.416452

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[0047] Figure 4 shows a schematic view of a printed circuit board arrangement to illustrate the method according to a second embodiment before a reflow soldering process.

[0048] Figure 5 shows a representation of the printed circuit board arrangement of Figure 4 in the soldered state,

[0049] Figure 6 shows a schematic sectional view of a printed circuit board arrangement according to a third embodiment of the invention before the reflow soldering process.

[0050] Figure 7 shows a schematic sectional view of a printed circuit board arrangement according to a fourth embodiment of the invention before the reflow soldering process.

[0051] Figure 8 shows a schematic sectional view of a printed circuit board arrangement according to a fifth embodiment of the invention before the reflow soldering process.

[0052] Figure 9 shows a schematic sectional view of a printed circuit board arrangement according to a sixth embodiment of the invention before the reflow soldering process, and

[0053] Figure 10 shows a schematic sectional view of a printed circuit board arrangement according to a seventh embodiment of the invention before the reflow soldering process.

[0054] Preferred embodiments of the invention

[0055] With reference to Figures 1 to 3, a printed circuit board arrangement 1 and a method for producing a reflow solder joint 7 on the printed circuit board arrangement 1 according to a first preferred embodiment of the invention are described in detail below.

[0056] As can be seen from Figure 1, the printed circuit board assembly 1 comprises a printed circuit board 2 with a bottom surface 20 and a top surface 21. On the top surface R.416452

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[0058] 21 is a reflow solder joint 7 (see Figure 2) formed between a wire 4 and the printed circuit board 2. The printed circuit board assembly 1 further comprises a soldering aid component 3, which in this embodiment is a funnel-shaped element with an opening for receiving the wire 4.

[0059] Wire 4 has a wire end 40, which is to be connected to the circuit board 2 by means of solder. The wire end 40 does not necessarily have to be in direct contact with the circuit board.

[0060] As indicated by the double arrow A in Figure 3, the soldering aid component 3 is movably arranged on the wire 4 before and during the soldering process.

[0061] Furthermore, a first solder deposit 5 is provided on the top surface 21 of the circuit board 2. The first solder deposit 5 is, for example, a solder paste applied to the top surface 21 of the circuit board 2.

[0062] To ensure a secure solder connection between the wire end 40 and the printed circuit board 2, the soldering aid 3 supports the reflow soldering process according to the invention in such a way that a sufficient amount of solder material remains in the area of ​​the wire end 40 when the solder in the first solder deposit 5 melts. As can be seen in Figure 2, the solder material in the first solder deposit 5 can completely fill the cavity below the soldering aid 3 to the printed circuit board 2 when soldered. The cavity does not necessarily have to be completely filled with solder.

[0063] The soldering aid 3, which is movable on the wire 4 during soldering, compensates for tolerances in the wire 4, which can be caused, for example, by an unsatisfactory wire cut. During the reflow soldering process, the soldering aid 3 ensures that the solder from the first solder deposit 5 does not flow away from the solder joint in excessive amounts. As can be seen in Figure 3, the wire end 40 is free of any tinning or similar coating.

[0064] The method according to the invention can thus produce a reliable reflow solder joint 7 on the printed circuit board assembly 1. Here, the solder joint 7 is of R.416452.

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[0066] Reflow soldering process formed both between the wire 4 and the circuit board and between the soldering aid component 3 and the circuit board.

[0067] The method according to the invention is particularly suitable for thicker wires, especially wires with a diameter > 1 mm or thicker stranded wires, i.e., stranded wires with a diameter of 1 mm. No additional connection technology is required for fixing the wires; instead, the wires, like SMD components, can be fixed to the printed circuit board in a single step using the reflow process.

[0068] A further advantage of the method according to the invention results from the fact that the underside 20 of the printed circuit board 2 can be free of components and, in particular, free of holes or the like. Thus, a flat underside 21 of the printed circuit board 2 can be provided without wire ends protruding through holes in the board to the underside. This allows for easy connection of a cooling device to the underside 21 of the printed circuit board 2. Furthermore, restricted areas on the underside and in the inner layers are avoided and can now be utilized.

[0069] During the reflow process, the soldering aid 3 is thus movably arranged. In the first embodiment, the soldering aid 3 is also movably arranged on the wire 4 before the actual soldering process. To prevent the soldering aid from being lost from the wire during handling, the opening provided in the funnel-shaped element for receiving the wire can preferably be designed such that a clearance fit is formed between the opening and the wire, allowing the soldering aid 3 to move freely but preventing it from simply falling off the wire.

[0070] A neck of the funnel-shaped element forms a hollow cylindrical section of a base body of the soldering aid component 3. To prevent the soldering aid component 3 from being unintentionally detached from the wire 4, it is also possible for the soldering aid component to be positioned relatively far from the wire end before the wire end is positioned at the solder joint. Once the wire end has been positioned at the first solder deposit 5, the soldering aid component 3 can then simply be slid towards the wire end. R.416452

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[0072] Figures 4 to 10 show further preferred embodiments of the invention, wherein identical or functionally identical parts are designated with the same reference numerals.

[0073] Figures 4 and 5 illustrate a second embodiment of the invention. As can be seen in Figure 4, before the reflow soldering process, the soldering aid 3 is fixed to the wire 4 by means of a second solder deposit 6. The second solder deposit 6 can be made of the same solder material as the solder material of the first solder deposit 5, or it can be a solder material with a lower melting point than the solder material of the first solder deposit 5. By fixing the soldering aid 3 to the wire 4 by means of the second solder deposit 6, the soldering aid 3 is thus securely fixed to the wire. This significantly simplifies the handling of the wire with the soldering aid. As can be seen in Figure 4, the wire with the fixed soldering aid 3 is then positioned at the soldering point where the first solder deposit 5 is located.

[0074] The wire 4 and the soldering aid 3 are then heated for reflow soldering to the circuit board 2. This is shown in Figure 5. The second solder deposit 6 melts before or simultaneously with the first solder deposit 5, causing the solder from the second deposit 6 to flow by gravity towards the wire end 4 and the circuit board 2. This makes the soldering aid 3 movable during the reflow soldering process. As shown in Figure 5, this results in a solder joint 7, which is a mixture of the solders from the two solder deposits 5 and 6. Sufficient solder material is present to bond the wire 4 and the soldering aid 3 to the circuit board 2. In the second embodiment, the soldering aid 3 is a hollow cylinder.

[0075] In the third embodiment shown in Figure 6, the soldering aid 3 is movably arranged (arrow A) on the wire 4 before the reflow soldering process. To prevent the soldering aid from being lost, the wire 4 is bent at approximately 45° at the wire end 40. This causes the wire end 40 to protrude slightly laterally from the wire, so that the soldering aid 3 has a smaller inner diameter, making it impossible for the soldering aid 3 to be lost from the wire. It should be noted that before positioning the wire at the solder joint on the circuit board 2, the bent wire end can be bent back so that the soldering aid 3 can be positioned as close as possible to the circuit board 2. Alternatively, the wire end 40 could also be ground down, so that despite the R.416452

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[0077] By bending the wire end, the distance between the movable soldering aid 3 and the circuit board 2 is kept as small as possible during positioning. Alternatively or additionally, the wire can also be crimped and / or compressed at the wire end to ensure it cannot be lost.

[0078] Figure 7 shows a fourth embodiment of the invention, wherein the soldering aid component 3 is designed as a double-cone-shaped element. In this embodiment, the soldering aid component 3 has projecting areas 31, particularly at the end facing away from the printed circuit board 2. The projecting areas 31 enable faster heating of the soldering aid component 3, thereby supporting the reflow soldering process.

[0079] Figure 8 shows a fifth embodiment of the invention, wherein the soldering aid component 3 is made of a strip material. The strip material encloses the wire 4 near the wire end 40 such that an opening 32 is formed to guide the wire 4 through the opening 32. The strip material can, for example, be arranged in a cross shape by overlapping the two ends of the strip material.

[0080] Figure 9 shows a sixth embodiment of the invention, wherein the printed circuit board arrangement 1 and the method additionally include a second solder deposit 6. As in the fourth embodiment, the soldering aid 3 is a double-cone-shaped element, with the second solder deposit 6 arranged on the protruding areas 31. As indicated by the double arrow A, the soldering aid 3 is arranged to be relatively movable relative to the wire 4 before the soldering process. The second solder deposit 6 is thus located exclusively on the soldering aid 3 before the reflow soldering process. Therefore, no connection is formed between the wire 4 and the soldering aid 3 via the second solder deposit 6 before the reflow soldering process. When the reflow soldering begins, the second solder deposit 6 also melts. The second solder deposit 6 has a second melting temperature that is equal to or lower than the first melting temperature of the first solder deposit 5.As a result, the solder from the second solder deposit 6 flows into the hollow cylinder area of ​​the soldering aid 3 towards the circuit board 2 due to gravity, wetting force, and capillary action, thus improving the solder joint 7 subsequently produced by reflow soldering. The soldering aid 3 remains movable throughout the entire soldering process. Figure 9 shows R.416452.

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[0082] the state before reflow soldering, in which wire 4 is positioned at the solder joint.

[0083] Figure 10 shows a seventh embodiment of the invention, which, like the sixth embodiment, has a second solder deposit 6. However, unlike the sixth embodiment, the second solder deposit 6 establishes a connection between the wire 4 and the soldering aid 3 before the reflow soldering process. The mobility of the soldering aid 3 relative to the wire 4 is then only achieved by melting the second solder deposit 6. Here, too, the second melting temperature of the second solder deposit 6 can be equal to or lower than the first melting temperature of the first solder deposit 5.

[0084] As explained in the preceding description, the soldering aid 3 enables the compensation of even larger tolerances between the wire 4 and the printed circuit board 2. Furthermore, the invention allows all components of the printed circuit board assembly 1 to be fixed to the printed circuit board 2 using a reflow soldering process. This eliminates the need for additional connection techniques such as through-hole technology (THT) or similar methods. As a result, the production costs of the printed circuit board assembly can be significantly reduced. The solution according to the invention provides a very reliable solder joint for all types of reflow soldering connections. In addition to the solder joint between the wire and the printed circuit board 2, a solder joint is also formed between the soldering aid 3 and the printed circuit board 2, and the wire is also connected to the soldering aid 3 by means of the solder.The soldering aid component 3 and the wire are preferably made of the same material, in particular copper.

[0085] As described above, the soldering aid component 3 can have three different geometric shapes. In particular, the material and design can be chosen such that, especially when the soldering aid component 3 is designed as a stamped-drawn part, an effect can be utilized whereby shrinkage at the neck end of the stamped-drawn part is used to hold the soldering aid component on the wire. The effect is such that the soldering aid component 3 is still movable relative to the wire, but not as movable as, for example, a cylindrical sleeve. R.416452

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[0087] Furthermore, according to the invention, tinning of the wire end 40 can also be omitted, which further reduces the manufacturing costs of the printed circuit board arrangement.

[0088] The method according to the invention is particularly suitable for thicker wires or wire strands with a diameter of, in particular, > 1 mm.

Claims

R.416452 - 14 - Claims 1. Method for producing a reflow solder joint (7) on a printed circuit board assembly (1), comprising the steps: - Applying an initial solder deposit (5) to a printed circuit board (2) to create a reflow solder joint (7), - Arranging a soldering aid (3) at one wire end (40) of a wire (4), - Positioning the wire end (40) with the soldering component (3) at the first solder deposit (5), and - Reflow soldering of the wire (4) and the soldering aid (3) to the printed circuit board (2) to create a reflow solder joint (7) between the wire and the printed circuit board and between the soldering aid (3) and the printed circuit board (2), - wherein during reflow soldering the soldering aid component (3) is movable at the wire end (40) of the wire (4) to allow a tolerance compensation between the wire (4) and the printed circuit board (2) for a contact-safe reflow solder joint (7).

2. Method according to claim 1, wherein the soldering aid component (3) is movably arranged on the wire (4) before reflow soldering.

3. Method according to one of the preceding claims, wherein the wire end (40) of the wire (4) is bent and / or squeezed and / or compressed before reflow soldering in order to hold the soldering aid component (3) securely on the wire (4).

4. The method of claim 3, wherein a second solder deposit (6) is arranged on the soldering aid component (3) or on the wire (4), which melts during reflow soldering to provide additional solder from the second solder deposit (6) for forming the reflow solder joint. R.416452 - 15 - 5. Method according to claim 4, wherein the second solder depot (6) does not provide a fixed connection between the soldering aid component (3) and the wire (4) prior to reflow soldering.

6. Method according to claim 4, wherein the second solder depot (6) provides a fixed connection between the soldering aid component (3) and the wire (4) prior to reflow soldering.

7. Method according to any one of claims 4 to 6, wherein the first solder depot (5) has a first melting temperature and the second solder depot (6) has a second melting temperature, wherein the first melting temperature is greater than or equal to the second melting temperature.

8. Method according to one of the preceding claims, wherein the soldering aid component (3) has a circumferentially closed area as a base body through which the wire (4) is passed.

9. Method according to claim 8, wherein the base body of the soldering aid component (3) is designed as a hollow cylinder area or wherein the base body is designed as a band encircling the wire.

10. Method according to one of the preceding claims, wherein projecting elements (31) are arranged on the soldering aid component (3) to increase heat supply to the soldering aid component (3) during reflow soldering.

11. Method according to one of the preceding claims, wherein the soldering aid component (3) and the wire (4) are made of the same material, in particular copper.

12. Method according to one of the preceding claims, wherein the wire end (40) of the wire (4) is untreated and in particular has no tinning.

13. A method according to any of the preceding claims, wherein a bottom side (20) of the printed circuit board (20) is free of components and holes, wherein in particular all components to be fixed to the printed circuit board (2) are fixed to the printed circuit board (2) by means of reflow soldering. R.416452 - 16 - 14. Method according to any of the preceding claims, wherein the wire (4) is a single-core wire or a stranded wire and in particular has a diameter greater than or equal to 2 mm.

15. Printed circuit board arrangement manufactured according to a method according to one of the preceding claims.

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