WO2004077901A2

WO2004077901A2 - Printed circuit board and method for fixing wired parts thereto

Info

Publication number: WO2004077901A2
Application number: PCT/EP2004/001983
Authority: WO
Inventors: Dietmar Birgel; Karl-Peter Hauptvogel
Original assignee: Endress+Hauser Gmbh+Co. Kg
Priority date: 2003-02-27
Filing date: 2004-02-27
Publication date: 2004-09-10
Also published as: WO2004077901A3; DE10308817A1

Abstract

Wired parts often cause a problem during overhead transport of a fitted printed circuit board, being able to fall out of the through bores because said wired parts are not glued or fastened to the printed board by means of retaining clips or snap-in devices. The invention solves said problem by means of a printed circuit board and a method for fixing wired parts thereto. The inventive printed circuit board (10) comprises a recess (24, 24') in a peripheral area of each through bore (20). Bent loose ends (22) of the connecting pins or connecting wires (18) of the wired part (16) are placed in said recesses (24; 24''). The quality of the soldered joint is improved especially during overhead soldering in a reflow soldering furnace as the solder (32) flows into the recesses (24 or 24') and the through bores (20) during the overhead soldering process in the reflow furnace. The length of the connecting wires (18) effectively wetted by the solder (32) is greater than during conventional soldering, making the soldered joint more secure.

Description

Printed circuit board and method for fixing wired components on the printed circuit board

The invention relates to a printed circuit board and a method for fixing wired components on the printed circuit board.

A "wired component" in the sense of this application is understood to mean one which is provided with at least two connecting pins or connecting wires. The connecting pins or connecting wires are known to be from a component side of the printed circuit board

Through holes in the circuit board are inserted and soldered on the other side of the circuit board, the so-called soldering side.

Various methods and devices are known for fixing wired components in their position on a printed circuit board or for holding them in their position relative to the printed circuit board, in particular when the components are to be soldered using an automatic method, for example wave soldering. Such a fixation is usually required after the circuit board has been fitted in the event of an uneven mass distribution of the wired components concerned and / or in those which have a tendency to tip over or otherwise in those which undesirably change their position during transport to the automatic soldering machine. For example, it is known to firmly glue such wired components to the circuit board or to fix them to the circuit board by means of mechanical devices, for example holding brackets or snap-in devices. Such devices are expensive and sometimes require

Changes to the housing of the relevant components. Another known way to fix the desired wired components is to insert or clamp the printed circuit board with the assembled wired components into a type of frame or cassette, which at the points where the components to be held are individual, usually have spring-loaded holding or pressing elements that press against the components and hold them in the desired position. Particular problems of fixation arise for an overhead transport of the printed circuit board with the critical wired components mentioned. It is important to fix the components in such a way that the connecting wires and thus the components do not fall out of the through holes in the circuit board. On the other hand, it is particularly advantageous to solder thermally critical components in an overhead arrangement in a reflow oven. In this overhead arrangement, the thermally critical components hang virtually under the circuit board and are therefore shielded by the circuit board itself from a heat source that mostly radiates from above in the reflow oven. Gluing the components to fix them in this case is possible but not always unproblematic and time-consuming because a drying time is required.

All known, above-mentioned methods for fixing critical components are complex, often costly and therefore undesirable.

The invention is therefore based on the object of improving the fixing of wired components on a printed circuit board for overhead transport in a simple and inexpensive manner.

This object is achieved according to the invention by a printed circuit board with at least two through holes for connecting pins or connecting wires of a wired component, a recess in a surface of each of the edge holes in the edge area

Printed circuit board is provided, in which recesses bent ends of the connecting pins or connecting wires are placed.

In a preferred embodiment of the circuit board according to the invention, the recess has a depth which corresponds to at least one diameter of the connection pins. In another preferred embodiment of the circuit board according to the invention, the recess is not deeper than half a corner of the circuit board in the area in question.

In other preferred embodiments of the circuit board according to the

Invention, the recess and / or the through hole are metallized.

In a further embodiment of the preferred embodiments of the printed circuit board according to the invention, the recess is created by at least one blind hole.

In yet another preferred embodiment of the circuit board according to the invention, the recess extends around the through hole.

The above-mentioned object is also achieved according to the invention by a method for fixing at least one wired component on the printed circuit board with the following method steps: a) at least two through holes for connecting wires or connecting pins of the wired component are drilled in the printed circuit board; b) on the side of the printed circuit board where the connecting wires or connecting pins of the component to be fixed are to be soldered, a recess is made in the edge region of each through hole; c) the connecting wires or connecting pins of the wired components to be fixed are from a component side of the

PCB inserted through the through holes; and d) the connecting wires or connecting pins are bent at the ends in such a way that they are sunk into the recesses when the printed circuit board and component are transported overhead and hold the component in its position and position relative to the printed circuit board. In a preferred embodiment of the method according to the invention, a) the circuit board is placed together with the fixed component in an overhead arrangement in a printing device, where the side of the circuit board where the recesses are arranged is printed with solder paste; and b) the circuit board is then soldered in a reflow soldering furnace.

In a further preferred embodiment of the method according to the invention, prior to soldering in the reflow soldering furnace, the printed circuit board is equipped with SMD components on the side printed with solder paste.

The particular advantage of the invention results from the fact that it enables the fixation of wired components on a printed circuit board in a simple manner and without great effort, by bending the connecting pins or connecting wires at the ends and thus hanging them in recesses when the printed circuit board is transported overhead are. Since the bent ends of the connection pins or connection wires can virtually submerge in the recesses, they do not protrude above the circuit board surface. This makes it possible to print the surface of the printed circuit board with the recesses and in this area in a screen printing system with solder paste, since no protruding ends of the connecting wires or pins hinder a squeegee of the screen printing system.

In addition, the invention makes other mechanical aids such as snap-in adapters or holding brackets for mechanically fixing critical wired components superfluous. Even gluing the components is not necessary. The invention is particularly suitable for overhead transport of the printed circuit board and for overhead soldering of thermally critical components fixed in this way in a reflow oven without additional holding frames or cassettes or additional mechanical holding devices related to the component being necessary. The production of the respective recess according to the invention in the edge region of a through hole is possible in a simple manner, for example as a blind hole, and can be carried out by a printed circuit board manufacturer; in a preferred embodiment it is provided that the recess as a blind hole with a larger diameter is placed over the actual through hole so that both are arranged concentrically.

The invention is particularly suitable for fixing strands or jumpers by mutually bending free conductor ends in the recesses, in addition, it is conceivable to have the bending of the connecting pins or connecting wires also carried out automatically as part of an automatic assembly process.

Since the ends of the connecting wires or connecting pins located in the recesses are also soldered, the mechanically stronger connection of the wired component is achieved by the larger amount of solder used for this.

The invention is described and explained in detail below, reference being made to preferred exemplary embodiments which are illustrated in the accompanying drawing. Show:

Figure 1 is a schematic cross-sectional view of a first embodiment of a circuit board according to the invention.

Fig. 2 is a schematic plan view of a circuit board according to Fig. 1;

Figure 3 is a schematic plan view of a second embodiment of a circuit board according to the invention. FIG. 4 shows a schematic cross-sectional illustration of the printed circuit board according to FIG. 3;

5 shows a schematic top view of a further embodiment of a printed circuit board according to the invention; and

FIG. 6 shows a schematic cross-sectional illustration of the printed circuit board according to FIG. 5.

For the sake of simplicity, the same elements or components are provided with the same reference symbols in the drawing.

In Fig. 1 is a printed circuit board 10 equipped on both sides and already soldered with various electronic components. For illustration purposes, two different surface-mounted components 12 and 14 (“SMD components) and a wired component 16 (“ THT component) are shown schematically here. For the sake of clarity, the representation of further components has been omitted here, but it is clear that usually more components are assembled on a circuit board. The illustrated wired component 16 has two connecting wires 18, which are preferably one before soldering

Overhead soldering in the reflow soldering oven, inserted into through holes 20 of the circuit board 10, the free ends 22 of the connecting wires 18 having been bent over. The through holes 20 may be provided with a sleeve, but as will be explained later, this is not absolutely necessary. It is clear that the few components shown in Fig. 1 are only examples. A circuit board is usually equipped with more SMD components. So far, the number of wired THT components has usually been kept very small, since each component required separate soldering. With the invention, however, it is now possible to solder the wired components 16 together with SMD components 12 in a reflow soldering furnace, as will be explained below. In addition to each through hole 20, preferably in its edge area, a recess 24 is made in the printed circuit board 10, which is preferably designed as a blind hole. A depth 26 of the blind hole, i.e. the recess 24, was based on the diameter 28 of the connecting wires 18 and the total thickness 30 of the printed circuit board 10. The depth 26 of the recess 24 is preferably chosen so that it is not greater than half the total thickness 30 of the printed circuit board 10 , but it should be at least equal to the diameter 28 of the connecting wires 18, so that the latter are preferably completely received in the recesses 24 and do not protrude beyond the printed circuit board 10.

As a result of the bent free ends 22 of the connecting wires 18, the wired component 16 hangs in the recesses 24 next to the through bores 20 when the printed circuit board 10 and the wired component 16 are moved into the overhead position shown in FIG. 1. If, as described above, the bent free ends 22 of the connecting wires 18 do not protrude beyond the surface of the printed circuit board 10, the printed circuit board 10 equipped in this way can be printed together with the wired THT component 16 with solder paste, for example in a suitable screen printing system, without this the free ends 22 of the connecting wires 18 hinder a doctor blade of the screen printing system. In the overhead arrangement illustrated in FIG. 1, the solder paste for the through bores 20 and the recesses 24 and for the other SMD components 12 to be placed on this side of the printed circuit board 10 can therefore be used in one operation. It is not a special soldering for the THT - Parts 16 required. After the solder paste has been applied to the locations provided for the assembly of the SMD components 12 and the SMD components have been placed there, the assembled printed circuit board 10 with the SMD components 12 arranged on top and as shown in FIG the overhead components located wired components 16 placed in a reflow soldering furnace and soldered there. The circuit board 10 protects even thermally critical wired components 16 from the usually from above onto the circuit board and the solder paste for the SMD components 12 acting heat radiation. The soldered circuit board 10 with SMD components 12 and 14 and the wired THT component 16 is shown schematically in FIG.

FIG. 2 schematically illustrates a top view of the printed circuit board 10 in the area of two wired THT components 16 and 16 ', which in the illustration selected here lie below the printed circuit board 10 and are therefore shown in broken lines. Recesses 24 and 24 'are clearly shown in the edge region of the through bores 20 and 20'. These recesses 24 and 24 'are preferably made like the recesses 24 shown in FIG. 1 by blind holes. The free ends 22 and 22 'of the connecting wires 18 and 18' are bent so that they come to rest in the recesses 24 and 24 'and do not protrude beyond them. It is clear that in special cases where, for reasons of convenience, further shortening of free ends 22 and 22 'of the connecting wires 18 and 18' is to be dispensed with, the recesses can also be designed as an elongated blind hole around the correspondingly longer free ends 22 and 22 'of the connecting wires 18 and 18' to be able to accommodate.

Another variant of the arrangement of recesses for receiving the free ends of the connecting wires is illustrated in FIG. 3. If the arrangement density of components on the printed circuit board 10 permits, the recesses 24 can be provided not only on one side of the through holes 20 but alternatively or in addition to one be arranged on the other side of the through holes 20. This arrangement is illustrated in FIG. 3 by recesses 24 ″ shown in dashed lines.

FIG. 4 shows a schematic cross-sectional illustration of a section of the printed circuit board 10 according to FIG. 3 for the area of a wired component 16 on an enlarged scale. This illustration illustrates the special way in which the invention improves the quality of the soldering. Characterized in that the solder paste before the soldering process on top of the recesses 24 and 24 "and the through holes 20 are applied, the solder 32 flows in the reflow oven during the overhead soldering process already described into the recesses 24 and 24 'and into the through holes 20 and wets the connecting wires 18 and in particular their free ends 22. Die effectively vom Lot 32 wetted length of the connecting wires 18 is greater than with conventional soldering, the soldering itself is therefore safer.

A particularly simple to manufacture arrangement of through bores and recesses is shown in FIG. 5 as a schematic top view of a further embodiment of a circuit board 10 according to the invention. Out

For reasons of simplification, only a single through hole 20 and a recess 24 are illustrated here, which is preferably drilled as a blind hole over the through hole 20. The recess 24 can also be milled around the through hole 20, as in the forms already described above.

FIG. 6 shows a schematic cross-sectional illustration of the printed circuit board 10 according to FIG. 5 on an enlarged scale. It has been shown in practice that it is particularly advantageous to metallize the through bores and the recesses. For the through hole 20 there is thus the known advantageous effect on the quality of the soldering, which is shown in conventional through holes with a metal sleeve. Through the metallization of the through hole 20 and the recess 24 according to the invention, the positive effect is thus also extended to the recess. The metallic change or

Lining of the through hole 20 and the recess 24 is denoted by "34" in FIG.

The method according to the invention for fixing a wired component 16 on a printed circuit board 10 and the subsequent soldering is described once again in summary below: After at least two through holes 20 for connecting wires 18 of the wired component 16 have been drilled into the printed circuit board 10, a recess 24 is made in the edge region of each through hole 20 on the side of the printed circuit board 10 where the connecting wires 18 of the wired component 16 to be fixed are to be soldered appropriate. Then the through bores 20 and the recesses 24 are preferably metallized before the wired component 16 is fitted. If the connecting wires 18 of the wired component 16 to be fixed have been inserted through the through holes 20 from an assembly side of the printed circuit board 10, the free ends 22 of the connecting wires 18 are bent over at the ends such that they are transported overhead when the printed circuit board 10 and component 16 are arranged recessed in the recesses 24 and hold the component 16 in its position and position relative to the printed circuit board 10.

Then the circuit board 10 together with the fixed wired component 16 in the overhead arrangement is placed in a printing device where the side of the circuit board 10 where the recesses are arranged is printed with solder paste. Since not only one but several wired components 16 are usually soldered together with SMD components 12, it is also useful for the process just described to be carried out for the

SMD components 12 required solder paste applied. After inserting the SMD components 12 into the solder paste, the printed circuit board 10 is soldered in the overhead arrangement in a reflow soldering furnace.

LIST OF REFERENCE NUMBERS

10 circuit board

12 SMD component

14 SMD component

16 wired THT component

18 connecting wires

20 through holes

22 free ends of (18)

24 recess

26 depth of (24)

28 diameter of (18)

30 total thickness of (10)

32 lot

34 metallization

Claims

claims

Printed circuit board (10) with at least two through bores (20; 20 ') for connecting pins or connecting wires (18; 18') of a wired component (16; 16 '), characterized in that in each case in an edge region of the through bores (20; 20') a recess (24, 24 ', 24 ") is provided in a surface of the printed circuit board (10), in which recesses (24; 24'; 24") bent free ends (22; 22 ') of the connecting pins or connecting wires (18; 18 ') can be placed.

Printed circuit board (10) according to claim 1, characterized in that the recess (24, 24 ', 24 ") has a depth (26) which corresponds to at least one diameter (28) of the connecting wires (18; 18').

3. Printed circuit board (10) according to one of claims 1 or 2, characterized in that the recess (24, 24 ', 24 ") is not deeper than half a thickness (30) of the printed circuit board (10) in the area concerned.

4. Printed circuit board (10) according to one of claims 1, 2 or 3, characterized in that the recesses (24, 24 ', 24 ") are metallized.

5. Printed circuit board (10) according to one of claims 1, 2, 3 or 4, characterized in that the through holes (20; 20 ') are metallized.

6. Printed circuit board (10) according to one of claims to 5, characterized in that the recess (24, 24 ', 24 ") is created by blind holes.

7. Printed circuit board according to one of claims 1 to 5, characterized in that the recesses (24, 24 ', 24 ") extend around the through bores (20; 20').

8. A method for fixing at least one wired component (16; 16 ') on a circuit board (10), characterized by the following method steps: a) in the circuit board (10) are at least two

Through bores (20; 20 ') for connecting wires (18; 18') or connecting pins of the wired component (16; 16 ') drilled; b) on that side of the printed circuit board (10) where the connecting wires (18; 18 ') or connecting pins of the component (16) to be fixed are to be soldered, in the edge region of each through hole (20; 20')

Recess (24; 24 '; 24 "); c) the connecting wires (18; 18') or connecting pins of the wired components (16; 16 ') to be fixed are inserted through the through holes (20 ; 20 '); and d) the connecting wires (18; 18') or connecting pins are bent over at the ends in such a way that when the printed circuit board (10) and component (16; 16 ') are transported overhead in the recesses (24 ; 24 '; 24 ") are arranged sunk and hold the component (16; 16') in its position and position relative to the printed circuit board (10).

9. The method according to claim 8, characterized by the following steps, a) the printed circuit board (10) is placed together with the fixed component (16; 16 ') in an overhead arrangement in a printing device where the side of the printed circuit board (10), where the recesses (24; 24 '; 24 ") are arranged, is printed with solder paste; and b) the circuit board (10) is then soldered in a reflow soldering furnace.

10. The method according to any one of claims 8 or 9, characterized in that the through holes (20; 20 ') and the

Recesses (24; 24 '; 24 ") after their completion in the Printed circuit board (10) are metallized before the wired component (16; 16 ') is assembled.

11. The method according to any one of claims 8, 9 or 10, characterized in that before the soldering in the reflow soldering furnace, the printed circuit board (10) is equipped with SMD components (12) on the side printed with solder paste.