System and method for connecting two printed circuit boards by means of a jumper, and use of the solder preform

Abstract

The invention relates to a system (8) comprising a solder preform (1) and a flexible jumper (2) with at least one connection element (3) which has two end regions (4), wherein the solder preform (1) is produced from solder and has two connection regions (5) each having at least one first through-hole (6), wherein in each case one end region (4) is guided through a first through-hole (6) and is fixed therein. The invention also relates to a method for connecting two printed circuit boards (10) by means of a jumper (2).

Description

[0001] System and method for connecting two printed circuit boards by means of a jumper, and use of the solder preform

[0002] The invention relates to a system consisting of a solder preform and a jumper, and to a method for connecting two printed circuit boards using a jumper. The invention further relates to the use of a solder preform.

[0003] Jumpers are used to connect two printed circuit boards. They comprise at least one connecting element, usually a copper wire, which creates an electrical and mechanical connection between the two boards. A jumper typically comprises several connecting elements arranged parallel to each other and surrounded by an insulating layer, such as a polymer. Jumpers are often designed to be flexible so that the two boards can be positioned at different angles to each other. This allows the two boards to be arranged in a spatially advantageous manner, reducing the space required for both boards.

[0004] The jumper is connected to the two circuit boards using a soldering process. The jumper is first placed on the circuit board and then soldered in a soldering oven.

[0005] Common soldering methods for SMD components include reflow soldering, wave soldering, and selective soldering. SMD components, also known as "surface-mounted devices," do not require PCB holes for assembly; instead, their contacts are soldered directly to designated contact pads on the circuit board. SMD components are mechanically placed on contact pads coated with solder paste on the circuit board using automatic placement machines and then soldered together, for example, in a single reflow soldering process.

[0006] THT components, on the other hand, have pin-shaped connecting wires that are inserted through metallized connection holes in the circuit board and soldered there by hand or using a wave soldering process, especially a selective soldering process. THT stands for "Through Hole Technique." This allows for a higher mechanical strength of the soldered connection than is possible with SMD components.

[0007] The backside reflow process enables the production of double-sided and mixed-sided populated circuit boards. For example, THT components can be arranged on a first side of the circuit board, possibly together with SMD components, and SMD components can be arranged on a second side. The SMD components on the first side are soldered in a preceding reflow soldering process. In the backside reflow process, the THT components arranged on the first side are soldered overhead together with the SMD components arranged on the second side in a single operation using a reflow soldering process. The heat required to melt the solder is essentially radiated from above onto the second side, while the first side is kept at a lower temperature.

[0008] After assembly, the THT components are fixed to the circuit board so that they remain in position when the circuit board is turned over. This is done either by adhesive bonding or by using the softlock technology described in DE 103 44 261 A1. With the softlock technology, the connection holes into which the connecting wires of the THT components are inserted are equipped with clamping collars whose diameter is slightly smaller than the outer diameter of the connecting wires. The connecting wires of the THT components are inserted through the constriction formed by the clamping collar. This creates a press fit that fixes the respective THT component in its position.

[0009] Jumpers are also considered THT components. However, because jumpers are often flexible, they cannot be picked up and automatically placed on the circuit board using a pick-and-place machine; instead, they must be manually placed individually onto the circuit board.

[0010] The object of the present invention is therefore to provide a system, a use and a method which enable a simple assembly of the printed circuit boards with a jumper.

[0011] According to the invention, the object is achieved by a system according to claim 1, a method according to claim 10 and a use according to claim 14.

[0012] With regard to the system, the object underlying the present invention is achieved by a system comprising a solder preform and a flexible jumper with at least one connecting element which has two end regions, wherein the solder preform is made of solder and has two connecting regions, each with at least one first through-bore, wherein in each case one end region is passed through a first through-bore and fixed in the latter.

[0013] By fixing the end regions of the jumper in the first through-holes, the jumper is connected to the solder preform and the jumper is fixed in its position, particularly that of its end regions. In this way, the jumper can be easily picked up by a pick and place machine using the solder preform and inserted into second through-holes provided for this purpose in a circuit board. The solder preform can be formed, punched or cast from a solid solder. The solder comprises an alloy of at least two components, one of the at least two components being a metal, such as tin, zinc, silver and / or copper. During the soldering process, particularly a backside reflow process, the solder preform is melted and provides the solder required to create the solder connection between the jumper and the circuit boards.

[0014] By securing the end portions in the first through-holes, the jumper is connected to the solder preform and can be automatically assembled on printed circuit boards as a system according to the invention. The end portions can be secured in the first through-holes, in particular, by soldering, press-fitting, or gluing. The end portions protrude from the first through-holes. In particular, the system consists of the solder preform and the jumper.

[0015] In one embodiment, the connecting element is a metallic wire. In particular, the connecting element is a copper wire.

[0016] In another embodiment, the jumper is designed as a THT component. THT stands for Through Hole Technique. THT components have pin-shaped connecting wires that are inserted through metallized through-holes in a circuit board and soldered there, for example, using a selective or wave soldering process. The two end areas are particularly pin-shaped.

[0017] Advantageously, the jumper comprises a plurality of connecting elements arranged parallel to one another and partially surrounded by an insulating layer. The insulating layer is made, for example, of a polymer such as a polyimide or polyester, in particular polyethylene naphthalate. In particular, the jumper consists of a plurality of connecting elements and an insulating layer that partially surrounds the connecting elements.

[0018] The two end regions are fixed in the first through-holes in particular by means of adhesive bonding, a press fit or soldering. With a press fit, the diameters of the first through-holes are matched to the outer diameters of the two end regions such that the end regions are held in the first through-holes. For example, the end regions can be fixed in the first through-holes by making the diameters of the first through-holes slightly smaller than the outer diameters of the end regions. This ensures that the end regions sit firmly in the first through-holes. In one embodiment, the solder preform has a depot region which has a larger volume of solder than the two connection regions. To produce a solder connection between the jumper and the two circuit boards, it is advantageous to provide a depot region which, for example,50%, especially 100%, more solder than the two bonding areas combined. The deposit area may have a greater thickness than the two bonding areas.

[0019] Preferably, the depot area is arranged between the two connecting areas. The depot area is then arranged below the at least one connecting element.

[0020] In a further embodiment, the two connecting regions each have a plurality of first through-holes. Jumpers typically have a plurality of connecting elements, so that the solder preform has a plurality of first through-holes. The first through-holes are arranged, in particular, opposite one another in the respective connecting regions. In particular, the solder preform has as many first through-holes as the jumper has at its end regions.

[0021] Advantageously, the solder preform is coated with a flux. The flux prevents oxidation of the solder when the preform is melted, thus ensuring a good solder connection between the jumper and the two circuit boards.

[0022] With regard to the method, the object underlying the present invention is further achieved by a method for connecting a printed circuit board to a jumper, the method comprising at least the following steps:

[0023] Providing at least one system according to one of the previous embodiments and two printed circuit boards each having at least one second through-hole,

[0024] Equipping the two circuit boards with at least one system so that one end region protrudes through a second through-hole,

[0025] Melting the at least one solder preform and soldering the at least one jumper to the two circuit boards in a backside reflow process.

[0026] By means of the method according to the invention, the system, comprising a jumper and a solder preform, is arranged in a simple and automated manner on two circuit boards and soldered to them. The solder preform is arranged on the two circuit boards, e.g. using a placement machine, in such a way that one of the end regions protrudes through the second through-hole of one of the two circuit boards and the other end region protrudes through the second through-hole of the other circuit board. The system is arranged between the two circuit boards or bridging the two circuit boards. The two circuit boards are typically arranged within a panel and connected to the panel edge and to one another by means of several webs. The webs are separated after the components have been fully assembled and soldered on the two circuit boards so that the circuit boards can be separated.The two circuit boards are then only mechanically and electrically connected via the jumper.

[0027] In the backside reflow process, the two circuit boards are arranged upside down, meaning the system is facing downwards or toward the ground. When the solder preform melts, a portion of the molten solder is drawn into the second through-holes by capillary force, so that the jumper is soldered to the second through-holes. The second through-holes are specifically metallized. Excess solder drips downwards.

[0028] The at least one system is provided, in particular, on a component belt. This allows the system to be easily picked up by the placement machine and mounted on the two circuit boards. The component belt contains a plurality of systems, which are fed to the placement machine one after the other.

[0029] Advantageously, the two end sections are secured in the second through-holes. This can be achieved by bonding, e.g., using a conductive adhesive, or by press-fitting, particularly with softlock technology.

[0030] In a further embodiment, the system is fixed to at least one of the two circuit boards using an adhesive. This holds the system in its position relative to the two circuit boards.

[0031] A further embodiment provides that at least one section of the two end regions protruding from the second through-holes is deformed in such a way that the system is held in its position by means of the at least one deformed section. The deformation of the at least one section can be a bending of the section. For example, the at least one section can be bent in the direction of the respective circuit board. In particular, both sections of the two end regions protruding from the second through-holes are deformed. With regard to the use, the object underlying this invention is achieved by using a solder preform for receiving a jumper and for populating the jumper on at least one circuit board. The flexible jumper has at least one connecting element with two end regions.The solder preform is made of solder and has two opposing connecting regions, each with at least one first through-bore, wherein the first through-bores are designed such that an end region can be passed through a first through-bore and fixed therein.

[0032] In some cases, the jumper is not used to mechanically and electrically connect two circuit boards, but rather is used on a single circuit board. However, it is usually used to connect two circuit boards.

[0033] The invention will be explained in more detail below with reference to the following figures, Fig. 1-8. They show:

[0034] Fig. 1a: a first embodiment of a solder preform.

[0035] Fig. 1 b: a second embodiment of a solder preform.

[0036] Fig. 2a: a design of a jumper.

[0037] Fig. 2b: an embodiment of a system according to the invention.

[0038] Fig. 3: a schematic representation of a printed circuit board panel.

[0039] Fig. 4: a schematic representation of the system according to the invention before assembly.

[0040] Fig. 5: a schematic representation of the system according to the invention after assembly.

[0041] Fig. 6: an alternative schematic representation of the system according to the invention after assembly.

[0042] Fig. 7: a schematic representation of the system according to the invention before the backside reflow process.

[0043] Fig. 8: A schematic representation of the jumper connected to the two circuit boards after the backside reflow process. The solder preform 1, the system 8 according to the invention, and the method according to the invention can be used in all types of field devices. Field devices are used to monitor and / or determine at least one process variable, for example a chemical or physical variable, of a medium and are known in a wide variety of designs from the prior art. In principle, all measuring devices or sensor arrangements that are used close to the process and that supply or process process-relevant information are referred to as field devices, including remote I / Os, radio adapters, and generally electronic components arranged at the field level.

[0044] A first embodiment of the solder preform 1 is shown in Fig. 1a. The solder preform 1 serves to accommodate a flexible jumper 2. The solder preform 1 is made of solder and has two opposing connection areas 5, each of which has at least one first through-hole 6. In the example shown, the two connection areas 5 each have three first through-holes 6. The solder preform is coated in Fig. 1 with an optional coating of a flux 13.

[0045] The design of the solder preform 1 shown in Fig. 1 b has a depot area 7. The depot area 7 has a larger volume of solder than the two connection areas 5 and thus ensures that sufficient solder is available to create a solder connection between the jumper 2 and the two circuit boards 10. The depot area 7 is arranged, for example, between the two connection areas 5.

[0046] Fig. 2a shows a typical design of a jumper 2. The jumper 2 has at least one connecting element 3 with two end regions 4. In the example shown, the jumper 2 has three connecting elements 3 arranged parallel to one another. The connecting elements 3 are, for example, metallic wires, in particular copper wires. Optionally, the at least one connecting element 3 can be partially surrounded by an insulating layer. The end regions 4 are, in particular, pin-shaped. The jumper 2 represents, in particular, a THT component.

[0047] Fig. 2b shows an embodiment of the system 8 according to the invention. The system 8 has a solder preform 1 and a jumper 2. The first through-holes 6 are designed such that an end region 4 can be passed through a first through-hole 6 and fixed therein. The end regions 4 can be fixed in the first through-holes 6 by gluing, soldering, or press-fitting. By fixing the end regions 4 in the first through-holes 6, the end regions 4 are fixed in a position. Thus, a placement machine can grip the system 8 and position the end regions 4 in second through-holes provided for them in printed circuit boards. Without the solder preform 1, the jumper 2 would be too flexible to be arranged in this way using a placement machine.

[0048] The jumper 2 is used to electrically and mechanically connect two printed circuit boards 10. Fig. 3 shows a schematic representation of a printed circuit board panel 14. Several printed circuit boards 10 are surrounded by a panel edge 11 and connected both to this edge and to one another by webs 15. The webs 15 are separated after the components have been fully populated and soldered on the printed circuit boards 10 so that the printed circuit boards can be separated. However, it is often desired that two or more printed circuit boards 10 are connected to one another. For this purpose, two printed circuit boards 10 can each be electrically and mechanically connected using a jumper 2. Due to the flexibility of the jumper 2 - both the connecting elements and the insulation layer are designed to be flexible - the printed circuit boards 10 can be arranged at different angles to one another, so that they can be arranged in a space-saving manner.

[0049] The further figures, Fig. 4-7, schematically illustrate the method according to the invention. Fig. 4 shows the first step of the method, namely the provision of the system 8 according to the invention and the two printed circuit boards 10, each of which has at least one second through-hole 12. The second through-holes 12 are designed in particular such that the end regions 4 can be passed through the second through-holes.

[0050] In a second step, the two circuit boards 10 are assembled, in particular automated, with the at least one system 8, as shown in Fig. 5. Assembly is carried out, for example, using an automatic assembly machine. During assembly, the system 8 is positioned on the two circuit boards 10 such that an end region 4 protrudes through a second through-hole 12. The system 8 is thus arranged between the two circuit boards 10 and connects the two circuit boards 10 to one another.

[0051] In order to mechanically connect the system 8 to at least one of the two circuit boards 10 and thus prevent the system 8 from falling down when the circuit boards 10 are turned over, adhesive 16 can be applied to at least one of the two circuit boards 10 or to both circuit boards 10 at a point onto which the system 8 is placed before assembly. The system 8 is thus held in position by means of the adhesive 16. In an alternative or additional embodiment, at least one of the two sections 17 of the end regions 4, which protrude beyond the second through-holes 12, is deformed such that the system 8 is held in position. In the example shown in Fig. 6, the two sections 17 are bent in the direction of the two circuit boards. Another possibility for holding the system 8 in its position is to fix the two end regions 4 in the second through-holes 12 by means of a press fit. This possibility is shown in Fig.7 shown.

[0052] For the subsequent soldering of the jumper 2 to the two circuit boards 10 in the backside reflow process, the two circuit boards are arranged overhead, as shown in Fig. 7. The two circuit boards 10 are then moved into a soldering oven together with the system 8 and soldered in a backside reflow process. Heat is supplied to the two circuit boards 10 essentially from above, i.e. from a surface of the circuit boards 10 facing away from the system. The heat causes the solder preform 1 to melt. The melting, in particular complete melting, of the solder preform 1 takes place in particular at a temperature which is above a liquidus temperature of the solder preform 1. Part of the molten solder is sucked into the second through-holes 12 by capillary forces and there ensures a solder connection between the end regions 4 and the second through-holes 12. Excess solder can drip downwards. If necessary,Part of the excess solder gets caught on the jumper 2, especially on the insulation layer 9, which is harmless for the further use of the circuit boards 10 and the jumper 2.

[0053] Finally, Fig. 8 shows the connection of the two circuit boards 10 with the jumper 2 after completion of the backside reflow process. The solder preform 1 is preferably no longer present after the backside reflow process.

[0054] List of reference symbols

[0055] 1 solder preform

[0056] 2 jumpers

[0057] 3 Connecting element

[0058] 4 End area

[0059] 5 Connection area

[0060] 6 first through hole

[0061] 7 Depot area

[0062] 8 Systems

[0063] 9 Insulation layer

[0064] 10 circuit board

[0065] 11 Benefit margin

[0066] 12 second through hole

[0067] 13 Flux

[0068] 14 PCB panels

[0069] 15 jetty

[0070] 16 glue

[0071] Section 17

Claims

Patent claims 1 . System (8) comprising a solder preform (1) and a flexible jumper (2) with at least one connecting element (3) which has two end regions (4), wherein the solder preform (1) is made of solder and has two connecting regions (5) each having at least one first through-bore (6), wherein in each case one end region (4) is passed through a first through-bore (6) and is fixed therein.

2. System (8) according to claim 1, wherein the connecting element (3) is a metallic wire.

3. System (8) according to one of claims 1-2, wherein the jumper (2) is designed as a THT component.

4. System (8) according to one of claims 1-3, wherein the jumper (2) has a plurality of connecting elements (3) which are arranged parallel to one another and are partially surrounded by an insulating layer (9).

5. System (8) according to one of claims 1-4, wherein the solder preform (1) has a depot area (7) which has a larger volume of solder than the two connecting areas (5).

6. System (8) according to claim 5, wherein the depot area (7) is arranged between the two connecting areas (5).

7. System (8) according to one of claims 1-6, wherein the two connecting regions (5) each have a plurality of first through-bores (6).

8. System (8) according to one of claims 1-7, wherein the solder preform (1) is coated with a flux (13).

9. System (8) according to one of claims 1-8, wherein the two end regions (4) are fixed in the first through-bores (6) by means of gluing, soldering or a press fit.

10. A method for connecting two printed circuit boards (10) by means of a jumper (2), the method comprising at least the following steps: Providing at least one system (8) according to one of claims 1-9 and two printed circuit boards (10) each having at least one second through-hole (12), Equipping the two printed circuit boards (10) with the at least one system (8) so that in each case an end region (4) protrudes through a second through-hole (12), Melting the at least one solder preform (1) and soldering the at least one jumper (2) to the two circuit boards (10) in a backside reflow process.

11. The method according to claim 10, wherein the two end regions (4) are fixed in the second through-bores (12).

12. Method according to one of claims 10-11, wherein the system (8) is fixed to at least one of the two circuit boards (10) by means of an adhesive (16).

13. Method according to one of claims 10-12, wherein at least one section (17) of the two end regions (4) protruding from the second through-bores (12) is deformed such that the system is held in its position by means of the at least one deformed section (17).

14. Use of a solder preform (1) for receiving a jumper (2) and for assembling the jumper (2) on at least one printed circuit board (10), wherein the solder preform (1) is made of solder and has two connecting regions (5) each having at least one first through-bore (6), wherein the jumper (2) has at least one connecting element (3) with two end regions (4), wherein the first through-bores (6) are designed such that in each case one end region (4) can be passed through a first through-bore (6) and can be fixed therein.

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