WO2009024583A1

WO2009024583A1 - Method for assembling electrical components equipped with terminal pins on a printed circuit board

Info

Publication number: WO2009024583A1
Application number: PCT/EP2008/060889
Authority: WO
Inventors: Oliver Kettenbaum; Manfred Friedl; Ludwig Kettl
Original assignee: Continental Automotive Gmbh
Priority date: 2007-08-22
Filing date: 2008-08-20
Publication date: 2009-02-26
Also published as: DE102007039612A1

Abstract

The object of the invention is to provide a simple and reliable method for assembling components equipped with terminal pins (24) on a printed circuit board (10). The method comprises the soldering of the terminal pin (24) of the component, being plugged through a bore (12) of the printed circuit board (10) from the top to the base, to a terminal pad (16) of the printed circuit board on the base, wherein a terminal pad (14) surrounding the bore (12) on the top of the printed circuit board (10) is configured on the top having a contour that is non-rotation symmetric with regard to the bore axis and is equipped with a soldering paste (34) before plugging in the terminal pin (24), the soldering paste being melted with the terminal pad (14) on top and with the terminal pad (16) at the base after plugging in the terminal pin (24) for forming the soldering of the terminal pin (24).

Description

description

Method for populating electrical components provided with pins on a printed circuit board

The present invention relates to a method for assembling components on a printed circuit board according to the preamble of claim 1.

In such a known method, the soldering of the inserted pin can be done for example by conventional hand soldering or so-called wave soldering.

Such a "through-hole mounting" offers the advantage of a comparatively high mechanical strength of the solder joint, as required for many components or applications of the assembled printed circuit board.

When hand soldering or wave soldering plugged through pins results in the requirement of a mechanical fixation of the device. In addition, another separate soldering step is required if the printed circuit board in question is also to be equipped with said surface mounted components ("SMD"). However, the use of SMD components is required in many applications, especially in space-critical applications. This is often z. B. for the field of automotive power electronics. Furthermore, the known assembly methods often require a comparatively large soldering area or a large "blocking area" on the printed circuit board.

Against this background, it has already been attempted to replace the manual soldering or wave soldering plug pins inserted by a so-called reflow soldering in order to work on the same conductor plate both wired components and SMD components in a single soldering process (reflow soldering) to equip.

In this known method (pin-in-paste or "THR" method) are stamped connection tabs on mechanical

Components such. B. connectors inserted through the corresponding holes (vias), previously applied to top terminal pads in the region of the vias by stencil pressure applied solder paste is partially displaced by the terminal tabs and pushed out of the feedthrough down.

By a subsequent reflow process, the soldering of the connecting tabs takes place on the one hand with the upper-side terminal pad and on the other hand with a lower-side

Connection pad of the printed circuit board (including connection in the through-connection).

So far, however, this method has only worked for special shape designs of the connection lugs. For example, the passing through of the terminal lug must not separate the solder paste into several parts which remain separate from one another even after the reflow process. Furthermore, it has turned out to be problematic to provide a quantity of solder paste in the area of the top-side connection pad which is sufficient for reliable soldering in the case of this method.

It is an object of the present invention to obviate the drawbacks noted above and to provide a simple and reliable method of mounting pin-mounted components on a printed circuit board.

In a mounting method of the type mentioned above, this object is achieved in that at the top of the circuit board surrounding the bore upper side terminal pad with respect to the bore axis non- formed rotational symmetry contour and is provided prior to the insertion of the terminal pin with a solder paste, which is melted after passing through the terminal pin to form the soldering of the terminal pin on the one hand with the top terminal pad and on the other hand with the bottom terminal pad.

In contrast to the known THR method, the provision of a sufficient amount of solder paste is facilitated in the invention by a special contour design of the top terminal pad, so that the inventive method can be used more universally, in particular with regard to the design of the terminal pin. A further advantage of the invention is that a skilful choice or orientation of the contour of the top-side connection pad makes it possible to save space or increase the packing density (of components on the circuit board).

In a particularly preferred embodiment with regard to the design of standard components, the connecting pin is substantially cylindrical. In this case, it has proven to be advantageous if the connecting pin has a diameter in the range of 40% to 80% of the bore diameter. For a given pin cross-section, the cross-section or the diameter of the through-connection should be as small as possible, but as large as necessary (for example, for realizing an automatic assembly).

A preferred application of the invention results for the

Assembly of an electrical or electronic component (active or passive). In one embodiment, the component is for example of a capacitor, in particular z. B. a film capacitor formed.

Advantageously, the method can be carried out largely automated (by means of a placement machine). In one ner embodiment is z. B. provided that the components are fixed to a component carrier belt fed in an automated assembly process of the circuit board.

In a particularly preferred embodiment, the

Equipping both the pin-mounted components and SMD components with a single reflow soldering process.

In one embodiment, it is provided that the contour has a contour section which is essentially rotationally symmetrical with respect to the bore axis and which extends in the circumferential direction over an angular range of at least 120 °.

In a more specific embodiment, this contour section is circular arc-shaped, wherein the corresponding circle center is at least approximately on the bore axis. Any offset between the circle center and the bore axis is preferably less than 50% of the diameter of the bore and / or less than 20% of the distance between the circle center and the arcuate contour section.

In a preferred embodiment it is provided that the contour has at least one contour section bulged in a radial direction.

An offset of the circular center point with respect to the bore axis is preferably provided in a direction which corresponds to the radial direction in which a bulged contour section of the connection pad is offset with respect to the bore axis.

In an embodiment which is advantageous with regard to the packing density to be achieved on the printed circuit board, it is provided that the printed circuit board in the radial Direction bulging contour portion is completely covered by a contour of the device.

The application of the solder paste to the upper-side terminal pad can, for. B. using a solder mask done (eg screen printing). Advantageously, in this case, all upper-side connection pads (also for optionally provided SMD components) of the printed circuit board can be printed using a standard solder mask of uniform thickness (for example in the range from 100 to 200 μm).

For the melting of the solder paste can advantageously be used on known methods (eg reflow oven, hot plate, infrared radiation, etc.). The maximum soldering temperature achieved in this process step is preferably in the range of 15O ⁰ C to 300 ⁰ C (eg 205-245 ⁰ C for SnPb solders, 235-26O ⁰ C for lead-free SnAgCu solders). In a preferred embodiment, the reflow system is a convection oven or a vapor phase oven.

The invention will be further described by means of embodiments with reference to the accompanying drawings. They show:

1 is a schematic side view of a printed circuit board in the region of a via,

2 is a view corresponding to FIG. 1 after application of a solder mask, FIG.

3 is a view corresponding to FIG. 2 during the printing of the printed circuit board upper side using the solder paste stencil, FIG.

4 shows a view corresponding to FIG. 3 after completion of the solder printing process (through-contact process). completely filled with solder paste; Connection pad covered with solder paste),

5 is a view corresponding to FIG. 4 at the beginning of a penetration of a connecting pin through the through-hole,

Fig. 6 is a view corresponding to FIG. 5 according to the

Passing through the pin,

7 is a view corresponding to FIG. 6 at the beginning of a reflow process, FIG.

FIG. 8 shows a view corresponding to FIG. 7 after completion of the melting process, FIG.

9 is a plan view of a connection pad with circular contour,

10 is a plan view of a connection pad with elongated contour,

11 shows an illustration for illustrating an optimized contour of an upper-side connection pad (a), whereby the contour of an associated lower-side connection pad (b) and a schematic side view (c) of the relevant printed circuit board area are also shown.

Fig. 12 is an illustration for illustrating a

Forming a blister strip for feeding film capacitors in an automated circuit board assembly process, and

Fig. 13 is a perspective view for illustrating the mounting of a film capacitor on a circuit board. Figs. 1 to 8 illustrate a method for automated loading and reflowing of wired components.

The region of a printed circuit board 10 shown in the figures comprises a bore 12 formed as a so-called through-connection, through which an upper-side connection pad 14 and a lower-side connection pad 16 are electrically connected to one another.

In the illustrated embodiment, a substrate 18 of the printed circuit board 10 also has printed conductors 20 and 22 on its upper side in the illustrated region.

FIGS. 1 to 8 illustrate, in this order, a through-mounting of a component, of which only one terminal pin 24 (of a plurality of pins of the component) is shown in the figures for the sake of simplicity. The one or more other pins of the same component are contacted in the same manner as described below for the pin 24.

Starting from the situation illustrated in FIG. 1, a solder mask 26 is first placed on the upper side of the printed circuit board 10 in the assembly process, as shown in FIG. 2.

The solder mask 26 is in the illustrated embodiment, a standard solder mask of a uniform thickness and has a recess 28 which is arranged in alignment with the top-side terminal pad 14.

Then, as shown in Fig. 3, by means of a doctor blade 30, which is moved in the direction of the arrow 32 (Fig. 3) on the solder mask 26, a solder paste 34 at the top

Pad applied 14 and partially pressed into the bore 12. Alternatively, the application of the solder paste te other methods into consideration, such as. Example, the use of a special solder paste print head (eg., System "Proflow" Fa. DEK).

Fig. 4 shows the situation after this application of the solder paste and the removal of the solder mask 26th

Then, in the automatic approach of the component, as shown in Fig. 5, the pin 24 is inserted from top to bottom through the bore 12, wherein the

Solder paste 34 is partially displaced by the pin 24 and partially taken to the PCB underside. In particular, for components from a certain size is practically only a placement in this direction (from above) into consideration.

The terms "top" and "bottom" are used here to distinguish the two sides of the printed circuit board and may, but do not have to correspond to the spatial orientations of these printed circuit board sides during the assembly process or when using the printed circuit board.

6 shows the resulting state after the insertion of the terminal pin 24.

Then, the solder paste 34 is thermally fused (reflow soldering), which is shown in Fig. 7 and finally leads to the situation shown in Fig. 8, in which the re-solidified solder paste 34 upper and lower menisci, via which the pin 24th is mechanically and electrically connected on the one hand with the upper-side terminal pad 14 and on the other hand with the lower-side terminal pad 16.

A peculiarity of the described assembly method is the non-rotationally symmetrical design of the upper connection pad 14 with respect to a bore axis 36 (FIG. 1) 34 is thus advantageously created a solder paste reservoir, as it were, which ensures the reliable formation of the apparent in Fig. 8 Meniscus.

Possible shapes for the top-side connection pad will be explained below with reference to FIGS. 9 to 11.

In the following description of further embodiments, the same reference numerals are used for equivalent components, each supplemented by a small

Letters for distinguishing the embodiment. In this case, essentially only the differences from the exemplary embodiment (s) already described are discussed and, moreover, reference is expressly made to the description of the preceding exemplary embodiments.

9 illustrates, in a top view, the configuration of an upper-side connection pad 14a with a circular contour line 40a, which extends rotationally symmetrically about a connection pin 24a, which is pushed through axially coaxially to a bore axis of a bore 12a. In the figure, dp denotes the diameter of fully cylindrical terminal pin 24a and that is, the diameter (inner diameter) of the hole 12a. The contour 40a of the upper-side connection pad 14a is thus rotationally symmetrical with respect to the bore axis. Although this geometrical design is suitable for the soldering process as such, it has other disadvantages and is not within the scope of the present invention. The rotationally symmetrical design is z. B. unfavorable when it comes to the terminal pad contour does not protrude beyond the component contour.

By contrast, FIG. 10 shows an example of a non-rotationally symmetrical contour 40b of an upper-side connection pad 14b. The terminal pad 14b is generally elongated and provides an advantageous reservoir with the pad areas relatively far from the terminal pin 24b for an additional amount of solder paste, which is drawn in reflow soldering to the pin 24b and into the bore 12b.

Fig. 11 illustrates an example of a pad symmetry which is particularly favorable for many applications. In the following, some design details which are particularly advantageous on their own or in combination will be explained below.

The partial view of Fig. IIa is a plan view of an upper-side terminal pad 14c. The partial view of Fig. IIb is a plan view of the associated lower-side terminal pads 16c and the partial view of Fig. 11c shows a FIGS. 1 to 8 corresponding side view of this embodiment.

As can be seen from FIG. 11a, the upper-side connection pad 14c has a contour 40c which is altogether non-rotationally symmetrical with respect to the bore axis (foot point of the arrow of the length r1). rl denotes the bore radius. However, a right-hand section of the contour 40c in the figure is substantially rotationally symmetrical with respect to the bore axis (here: as a circular arc section with the radius r2). This circular arc portion of the contour line 40c extends over an angular range of about 170 °.

Further, however, the contour 40c also includes a contour portion located on the left side in the figure, which is bulged in a radial direction (to the left). This bulged contour portion is formed in the illustrated embodiment by a likewise circular arc-shaped with a radius r3 extending portion. The two transitions between the two circular arc regions are formed symmetrically relative to a center line extending horizontally in the figure from respective rectilinear sections, as can be seen in FIG. IIa. Another peculiarity of the illustrated geometry is that the circle center of the right circular arc portion in the figure (radius r2) with respect to the bore axis of the bore 12c to the left (ie towards the bulged area) is offset. The bases of the radius arrows rl and r2 do not coincide.

The underside connection pad 16c shown in FIG. IIb is provided with a circular contour in this exemplary embodiment.

FIG. 11c illustrates in a side view the mutual position of the bore 12c and the connection pads 14c and 16c on the substrate 12c. tb denotes the thickness of the printed circuit board 10c. In the illustrated embodiment, the dimensions shown are selected as follows:

r1 = 0.60mm r2 = 1.60mm r3 = 1.10mm r4 = 0.90mm dh = 2 x rl = 1.2mm sl = 0.90mm s2 = 0.85mm s3 = 0, 68 mm s 4 = 4.20 mm tb = 1.5 mm

These dimensions are of course only to be considered as examples and can be modified depending on the specific application.

A preferred use of the assembly process is the automated assembly of electrical or electronic components, each provided with a plurality of pins ("wired components"). In this case, a correspondingly shaped carrier belt for an automated supply of the individual components in the context of a series production of circuit arrangements can be provided for the relevant component.

FIG. 12 illustrates the configuration of a carrier belt 5Od, designed as a blister band, for the assembly with film capacitors, one of which is shown in FIG. 12 and denoted by 52d.

The length dimensions contained in the figure are each given in mm and again only to be understood as an example.

Fig. 13 illustrates the mounting of the film capacitor 52d on a circuit board 10d. In this case, the two connection pins 24d of the capacitor 52d are inserted through an automatic insertion machine simultaneously through the corresponding bores 12d of the printed circuit board 10d (compare the above description with reference to FIGS. From this illustration, a further advantageous embodiment of the assembly process can be seen, which consists in that each of the contoured portions of the upper-side connection pads 14d bulged out in the radial direction is completely covered by a contour of the relevant component (here: capacitor 52d). This minimizes the board area required for contacting the device, which is a great advantage for achieving a high packing density.

In summary, the invention makes available the use of the so-called "pin-in-paste" method for a large number of electrical or electronic components. In particular, the following advantages can be achieved:

It is an automatic assembly with existing placement machines possible. - A solder joint inspection for quality assurance is z. B. by "AOI" or "AXI" possible.

- With appropriate arrangement geometry results in a minimum Sperrflächenbedarf to increase the PCB packing density.

With simultaneous assembly of the circuit board with SMD components, an additional manufacturing step of wave soldering can be omitted. All soldering can be realized by a single reflow soldering.

- A simultaneous assembly of wired components as well as SMD components offers a significantly better price / performance ratio compared to a pure SMD assembly.

The method can be realized with a simple and inexpensive solder stencil. In particular, z.

B. no graded template mandatory. Also on a partial thickening of the paste order (eg paste imprint), which would be costly, can be advantageously dispensed with.

The invention is particularly suitable for the production of circuit arrangements, with which an electronics, in particular power electronics, is provided for a motor vehicle.

As far as the manufacture of the components to be mounted on a printed circuit board according to the invention is concerned, they can be suitably designed with regard to the temperature load to be expected during the soldering process. In one embodiment it is provided that already at the

Production of the relevant component, a temperature control of the device and a subsequent electrical function test takes place, this temperature corresponds to the temperature required for the process according to the invention of the device. In this way, any components that do not withstand the thermal stresses during assembly can be sorted out as rejects during their production. Only the suitable components are then used for equipping.

Claims

claims

A method of assembling components (52) provided with pins (24) on a circuit board (10), comprising soldering the component through a hole (12) thereof

Printed circuit board (10) from top to bottom inserted pin (24) of the device with a bottom terminal pad (16) of the circuit board, characterized in that at the top of the circuit board (10) surrounding the bore (12) upper side terminal pad (14) with a with respect to the bore axis (36) non-rotationally symmetrical contour (40) is formed and before passing through the terminal pin (24) with a solder paste (34) is provided after passing through the terminal pin (24) for

Forming the soldering of the connecting pin (24) on the one hand with the upper-side terminal pad (14) and on the other hand with the lower-side terminal pad (16) is melted.

The method of claim 1, wherein the terminal pin (24) is substantially cylindrical.

3. The method of claim 2, wherein the terminal pin (24) has a diameter (dp) in the range of 40% to 80%, in particular 50% to 70%, of the diameter (ie) of the bore (12).

4. The method according to any one of the preceding claims, wherein the component (52) is an electrical or electronic

Component is.

5. The method according to any one of the preceding claims, wherein the contour (40) has a respect to the bore axis (36) substantially rotationally symmetrical contour portion which extends in the circumferential direction over an angular range of at least 120 °. Method according to one of the preceding claims, wherein the contour (40) has at least one contour section bulged in a radial direction.

The method of claim 6, wherein the curved in the radial direction contour portion of a contour of the device (52) is completely covered.