EP3729909A1

EP3729909A1 - Flexible flat heater, and method for producing it

Info

Publication number: EP3729909A1
Application number: EP18825674.7A
Authority: EP
Inventors: Leonhard Vetter; Jürgen PROKOP; Moritz Hamacher; Nico Fischer; Sebastian Lange
Original assignee: DBK David and Baader GmbH
Current assignee: DBK David and Baader GmbH
Priority date: 2017-12-19
Filing date: 2018-12-18
Publication date: 2020-10-28
Also published as: DE102017130508A1; WO2019121772A1

Abstract

The invention relates to a flexible flat heater having a plurality of PTC heating components formed from SMD elements, and to a method for producing such heaters. For the purpose of heat conduction and/or for optimizing heat distribution, the conductor tracks are wider than a length of the SMD elements.

Description

Flexible planar heater and method for its production

description

The invention relates to a flexible planar heater according to the preamble of patent claim 1 and a method for its production.

Applicant's EP 1 648 199 A1 shows a heater in which the actual heating element is provided with e.g. is structured heat conductor foil produced by stamping or etching. This is fixed on a Mikanitteil and is therefore not flexible.

The two related publications WO 2013/087511 and DE 11 2012 005 238 T5 describe a planar ohmic heater with PTC heating elements. PTC heating elements have a positive temperature coefficient, so that their ohmic resistance increases with increasing heat, and thus the heating power is throttled. This makes PTC heating elements self-regulating.

A disadvantage of such heaters is that they are rigid and must always be installed in a flat position.

DE 10 2011 000 765 A1 discloses a heater with a printed circuit board in which a plurality of through-holes is arranged. About the

Through holes each extending an SMD component, which serves to generate the heat of the heater. In a direction perpendicular to the circuit board, a fluid to be heated is passed, which flows through the through-holes and is thereby heated by the SMD components.

Furthermore, it is known to perform flexible heaters flexible so that they are used for heating non-planar components, such. of tubes can serve.

The document EP 0 320 862 A2 discloses PTC heating elements which are arranged between two flat metal nets and thus electrically contacted. On insulating housing closes to the outside. The heater thus formed is considered flexible and the PTC heating elements are disclosed as relatively small.

A disadvantage of such flexible planar heaters is the complex production and the limited flexibility in the application.

In contrast, the invention is based on the object to provide a flexible planar heater and a method for its production, in which the production cost is reduced, and the flexibility in assembly is improved.

Furthermore, the invention is based on the object to improve the heat dissipation of the SMD components and the heat distribution over the surface of the heater or its flexible printed circuit board.

This object is achieved by a heater having the features of patent claim 1 and by a method having the features of claim 13.

Further advantageous embodiments of the invention are described in the dependent patent claims.

The claimed flexible planar heater has a flexible printed circuit board consisting of a carrier film preferably of polyimide, conductor tracks (for example of copper) and preferably at least partially applied solder mask or a cover film. On a first side several PTC heating elements are attached. According to the invention, the PTC heating elements are formed by SMD components. These can be mounted by an SMD placement machine, whereby the installation cost of the heater is reduced.

According to the invention, the conductor tracks of the heater are made wider than is necessary for conducting the current for the SMD components. Thus, the width of the conductor tracks can be greater than the length of the SMD components. This increases the heat dissipation from the SMD components to the printed conductors. From there, the heat - preferably transmitted through the carrier film - to the component to be heated. In a particularly preferred embodiment of the heater, its power supply is implemented via an SMD plug. This mounting technology can also be mounted particularly easily by the SMD placement machine on the printed circuit board.

On one of the first side opposite the second side (for example, bottom side), an adhesive layer is preferably provided, via which the heater can be glued to a component to be heated. The component to be heated is e.g. a pipe, on the outside of the heater of the invention is adhered.

Alternatively, the heater can also be clamped or pressed against the component to be heated. So it is e.g. possible to dimension a distance between two mutually opposite edges of the heater so that this distance corresponds approximately to the circumference of the pipe to be heated. Then the heater is bent on the outer circumference of the pipe and the two mentioned edges come into close proximity to each other. Finally, the two edges are passed over a tensioning element, e.g. a clamping clasp made of spring steel, stretched together.

On the second side of the flexible circuit board and a heat distribution layer may be preferably made of copper. In the aforementioned development with the adhesive layer, the heat distribution layer is attached directly to the second side of the circuit board, while the adhesive layer is attached to the heat distribution layer.

On the first side, preferably an electrical and / or thermal insulation layer is preferably made of silicone, which covers the conductor tracks and SMD components. In the case of electrical insulation, this serves as a contact protection. In the case of thermal insulation, the heat of the heater is delivered toward the second side (e.g., bottom).

In a particularly preferred embodiment of the heater according to the invention, the conductor tracks are made thicker than is necessary for conducting the current for the SMD components. Thus, the heat dissipation from the SMD components to the conductor tracks further increased. From there, the heat is transferred to the component to be heated, preferably through the carrier film.

The interconnects are separated by main recesses, wherein preferably the elongated interconnects and the elongated main recesses are arranged parallel to each other. Then, the SMD components can extend transversely across the main recesses, in each case from one conductor track to the other conductor track.

Preferably, the main recesses, together with connection recesses, form a meandering, continuous, overall recess. This can be easily produced by etching production technology.

By means of the continuous overall recess, the tracks can be divided into two groups. In this case, the interconnects of the first group are connected to one another via a first interconnect conductor, while the interconnects of the second group are connected to one another via a second interconnect interconnect. Those in the interconnect traces with their respective groups of traces may be connected to a respective electrical potential. Then, the conductor tracks of the first group can be arranged with the conductor tracks of the second group, in particular parallel to one another and alternately.

Also, the interconnect traces may be wider and / or thicker than necessary to conduct the current to the traces and the SMD components. Thus, the width of the interconnect tracks can be greater than the length of the SMD components. This increases the heat dissipation from the SMD components via the conductor tracks to the interconnect tracks. From there, a portion of the heat - preferably transmitted through the flexible circuit board - to the component to be heated.

Preferably, the two connecting tracks are arranged transversely to the conductor tracks and transversely to the main slots. In a particularly preferred development, the two interconnect interconnects extend along two mutually parallel edges of the flexible printed circuit board. The interconnects and optionally also the interconnect traces may be perforated to increase the flexibility of the heater.

A modular development of the heater according to the invention has a plurality of first groups of conductor tracks, which are electrically contacted with each other, and a plurality of second groups of conductor tracks, which are electrically contacted with each other.

The heater or its modules can be simply rectangular in terms of device technology and manufacturing technology. However, deviating forms are also conceivable for optimally covering corresponding shapes of components or surfaces to be heated.

In a preferred variant of the heater according to the invention whose heat distribution is distributed unevenly over its surface. In this way, components to be heated can be optimally heated in special applications. For this purpose, the SMD components may have different power consumption and heat dissipation and / or be distributed unevenly distributed over the surface. Thus, the variability of the heater according to the invention is increased.

The tracks are always parallel to each other so that they can be bridged by the SMD components. In this case, a straight extension but also a curved extension of the tracks is possible. This also increases the variability of the heater according to the invention.

The method according to the invention serves to produce a heater as described above and has the step of: automatically loading the SMD components by means of an SMD placement machine. Thus, the installation cost of the heater is reduced.

A preferred embodiment of the method has the additional step:

- Automatic placement of an SMD connector using the SMD placement machine. A preferred embodiment of the method comprises the preceding step: etching a continuous overall recess. This step is associated with the manufacture of the flexible circuit board. With this step, the conductor tracks are manufactured.

In a further development of the method, an insulating layer is attached to the first side of the flexible conductor plate, which also covers the PTC heating elements. This serves as a contact protection and / or to direct the heat flow of the PTC heating elements down.

In a preferred embodiment of the method, the size and / or the power of the heater is flexibly selected or reduced by the step: disconnecting an unnecessary part of the printed circuit board, e.g. by cutting parallel to the conductor tracks and main recesses. The separation is preferably carried out in modules, the separated part then has a first and a second group of conductor tracks.

Particularly simple is the production of the above-described arrangement consisting of two heaters, when the electrical contacts of the two groups of tracks via SMD components formed as O-ohm resistors by means of the SMD placement machine.

Two embodiments of the heater according to the invention consisting of two modules are shown in the figures. With reference to the figures, the invention will now be explained in more detail.

Show it:

1 shows a perspective view of part of the heater according to the invention according to a first embodiment consisting of two modules,

FIG. 2 shows a plan view of the heater according to the invention from FIG. 1 without SMD components,

FIG. 3 shows in a cross-section a part of the heater from FIGS. 1 and 2,

Figure 4 in a cross section a part of the heater of Figures 1 to 3 and

5 shows in a cross section a part of the heater according to a second embodiment. Figure 1 shows a perspective view of the embodiment of the flexible planar heater 1, which has a substantially rectangular flexible printed circuit board 2. At its upper side (visible in FIG. 1), two heating units or modules 3 which are adjacent to one another are provided, the dividing line of which is shown in dashed lines, and which are explained in greater detail with reference to FIG.

Each module 3 has a multiplicity of PTC heating elements 4, which are arranged in the manner of a matrix and are each formed by SMD components 4. They were positioned on the flexible circuit board 2 with an SMD placement machine and then soldered in an oven.

The heater 1 is arranged on the outer circumference of a tube 6, whereby a fluid to be heated flows through the tube 6 approximately along the longitudinal axis 8 of the tube 6. In this case, the heater 1 is so bendable by the flexible design of its printed circuit board 2 that he or she can be easily adapted to the curvature according to the outer radius R of the tube 6. The SMD components 4 (theoretically) are arranged tangentially to the outer wall of the tube 6. The length of the SMD components 4 is dimensioned so short that a comparatively small radius of curvature R and thus a strong curvature of the heater 1 is possible. For this purpose, for example, SMD components 4 of the housing 1210 form.

The power supply of the (left in Figure 1 and completely shown) module 3 via an SMD connector 10, which (also from the SMD placement) is placed on a tab of the carrier film 5 of the heater 1.

The electrical contacting and thus power supply of the module 3 (which is only partially shown in FIG. 1) takes place via two so-called O-ohm resistors formed as SMD bridge components 12, which have a distance (shown in FIG. 2) between the two modules 3 bridged.

Figure 2 shows a plan view of the top of the non-curved flexible printed circuit board 2 of the heater 1 with its two modules 3, wherein the SMD components. 4 have been omitted or are not yet set up. Thus, FIG. 2 shows for each module 3 (uncovered) printed conductors 14 of a first group which alternate with printed conductors 16 of a second group. The interconnects 14 of the first group are formed integrally with a first interconnect conductor 18, while the interconnects 16 of the second group are formed integrally with a second interconnect interconnect 20. In this case, the two first interconnection interconnects 18 of the two modules 3 extend along a first edge 22 of the flexible printed circuit board 2, while the two second interconnect interconnects 20 of the two modules 3 extend along a second edge 24 of the flexible printed circuit board 2.

The two mutually parallel edges 22, 24 of the flexible printed circuit board 2 are curved in the assembly of the heater 1 on the outside of the tube 6 (see Figure 1) corresponding to the outer radius R of the tube 6.

Each module 3 has a continuous meandering overall recess, at which the top of the flexible printed circuit board 2 is not covered with copper. Each overall recess consists of an alternating sequence of main recesses 26, the length of which approximately correspond to those of the conductor tracks 14, 16, and connection recesses 28, the length of which corresponds approximately to the width of the conductor tracks 14, 16. The main recesses 26 are aligned parallel to the conductor tracks 14, 16, while the connection recesses 28 are aligned perpendicular thereto and thus parallel to the two edges 22, 24 of the carrier film 5 and parallel to the SMD components 4.

The main recesses 26 provide an alternating series of wider main recesses 26 across which extend a plurality (six in the illustrated embodiment) of SMD components 4 and respective narrower main recesses 26 which do not extend SMD components.

Between the two modules 3, a further main recess 30 is provided, which not only separates a conductor track 14 of the first group from a conductor track 16 of the second group, but also separates the two first connection conductor tracks 18 and the two second connection conductor tracks 20 from each other. To do this extends the other main recess 30 over the full width of the heater 1 and the flexible circuit board. 2

In device-simple manner, only the first module 3 is provided with an SMD connector 10, are supplied via the two modules 3 with power. In this case, the further main recess 30 is bridged by two O-ohm resistors designed as SMD bridge components 12 (shown in FIG. 1). More specifically, the two first connection patterns 18 and the two second connection patterns 20 are connected to each other.

In FIG. 2, neither the SMD plug 10 nor the multiplicity of SMD components 4 nor the two SMD bridge components 12 are shown, but in each case only the associated solder pads. These solder pads are electrically connected via respective small bridges with the tracks 14, 16 or with the interconnect tracks 18, 20.

In addition, in FIG. 2, as an alternative for each SMD bridge component 12, two circular solder pads can be seen, to which leads (not shown) can be soldered, in order to electrically connect the two modules 3 with each other. In particular, in this case, the heater can be significantly more curved in the transition region between the two modules 3, as allow the populated areas of the modules 3. Thus, the heater can also be applied on both sides of a rounded edge of a component to be heated. The dashed line from FIG. 1 then extends along the rounded edge of the component to be heated. On both sides of the rounded edge, e.g. respective level to be heated surfaces.

The interconnects 14, 16 and the interconnect tracks 18, 20 are perforated to maximize the flexibility of the two modules 3.

FIG. 3 shows, in a sectional view, a single PTC heating element designed as an SMD component 4, which is fastened to a small section of the flexible printed circuit board 2. The two terminal regions of the SMD component 4 are soldered to a respective solder pad 34 with a respective solder 32. The two solder pads 34 of SMD components 4 are formed from copper and in each case formed integrally with the conductor tracks 14, 16 of two different groups. Between the two solder pads 34, one of the main recesses 26 is provided.

FIG. 3 shows that solder resist 36 is provided in the main recess 26. Also between the solder pads 34 and the associated (not shown in Figure 3) printed conductors 14, 16 Lötstopplack 36 is provided. In contrast, the solder pads 34 are of course not covered with solder mask 36.

Furthermore, FIG. 3 shows the flexible printed circuit board 2, on the upper side of which the SMD components 4 are arranged, and through which the heat (in FIG. 3 downwards) is emitted to the tube 6 during operation of the heater 1 according to the invention.

In order to increase this effect and additionally as contact protection, the entire upper side of the heater 1 is coated with an insulating layer 38 made of silicone. The insulating layer 38 forms a substantially flat surface upwards.

FIG. 4 shows a cross section through a small section of the heater 1 according to the invention with the flexible printed circuit board 2, wherein one of the conductor tracks 14 or

16 is shown cut. On both sides of the conductor track 14, 16, one of the main recesses 26 is provided.

Shown is the layered structure of the carrier film 5, preferably of polyimide, the conductor tracks 14, 16 made of copper, which are made by etching the initially completely coppered circuit board 2, and solder mask 36. Instead of the solder stop 36 can also be a Cover be provided. Finally, the insulating layer 38 described with reference to FIG. 3 is shown.

FIG. 4 shows that these main recesses 26 and the printed conductors 14, 16 are completely covered with solder mask 36, wherein only the solder pads 34 (shown in FIG. 3) remain free, so that the contact regions of the SMD components 4 pass through the solder 32 can be contacted electrically. 5 shows in a sectional view a section of a second embodiment of the heater according to the invention comparable to the illustration of Figure 3. Here, the difference to the first embodiment according to Figures 1 to 4 is seen in that at the bottom of the flexible circuit board 2 is a full-surface Heat distribution layer 40 is mounted made of copper.

In FIGS. 3 and 4 on the underside of the flexible printed circuit board 2 and in FIG. 5 on the underside of the heat distribution layer 40, a self-adhesive layer may be applied. About this, the heater 1 is simply glued to the component to be heated, in the illustrated embodiments of the pipe 6.

Notwithstanding the embodiments shown, all main recesses 26 can be bridged by SMD components 4.

Notwithstanding the exemplary embodiments shown, it is also possible to provide a cover film instead of solder mask 36.

All mentioned and explained features can be combined according to the invention as desired.

Disclosed are a flexible planar heater with a plurality of PTC heating elements, which are formed by SMD components, and a method for producing such heaters. For heat conduction and / or for optimizing the heat distribution, the strip conductors are made wider than a length of the SMD components.

LIST OF REFERENCE NUMBERS

1 heater

2 flexible circuit board

3 module

4 PTC heating element / SMD component

5 carrier film

6 to be heated component / tube 8 longitudinal axis

10 SMD plugs

12 SMD bridge component

14 trace of the first group

16 trace of the second group

18 first interconnect trace

20 second interconnect trace

22 first edge

24 second edge

26 main recess

28 connection recess

30 more main recess

32 soldering

34 solder pad

36 solder mask

38 insulating layer

40 heat distribution layer

R outer radius

B width

L length

Claims

claims

1. Flexible flat heater with a flexible printed circuit board (2), on the first side of several PTC heating elements are arranged, wherein the PTC heating elements are SMD components (4), characterized in that a width (B) of conductor tracks (14 , 16) is greater than a length (L) of the SMD components (4).

2. Flexible planar heater according to claim 1, wherein on one of the first side opposite the second side of the flexible printed circuit board (2) an adhesive layer is provided, via which the heater to a component to be heated (6) are glued can.

3. A flexible planar heater according to claim 1, wherein on one of the first side opposite the second side of the flexible printed circuit board (2) a heat distribution layer (40) is provided.

4. Flexible planar heater according to one of the preceding claims, wherein on the first side an electrical and / or thermal insulating layer (38) is provided, which covers the conductor tracks (14, 16) and SMD components (4).

5. Flexible planar heater according to claim 4, wherein on the one hand the conductor tracks (14, 16) and the SMD components (4) and on the other hand the insulating layer (38) a Lötstopplack (36) and / or a cover film are provided / is ,

6. Flexible planar heater according to one of the preceding claims, wherein the conductor tracks (14, 16) are designed with increased thickness.

A flexible planar heater according to any one of the preceding claims, wherein the tracks (14, 16) are separated by main recesses (26), and wherein the tracks (14, 16) and the main slots (26) are arranged parallel to each other are.

8. A flexible planar heater according to claim 7, wherein the main recesses (26) together with connecting recesses (28) form a meandering, continuous overall recess.

9. Flexible planar heater according to one of the preceding claims, wherein printed conductors (14) of a first group are connected to one another via a first connecting printed conductor (18), and printed conductors (16) of a second group are connected via a second connecting printed conductor (20). connected to each other.

10. A flexible planar heater according to claim 9, wherein the two connecting tracks (18, 20) transversely to the conductor tracks (14, 16) and along two edges (22, 24) of the flexible printed circuit board (2).

11. A flexible planar heater according to claim 9 or 10 comprising a plurality of first groups of conductor tracks (14) which are electrically contacted with each other, and with a plurality of second groups of conductor tracks (16) which are electrically contacted with each other.

12. Flexible planar heater according to one of the preceding claims with a non-uniform heat distribution.

13. A method for producing a flexible planar heater (1) according to any one of claims 1 to 12 with the step:

- Automatic loading of the SMD components (4).

14. The method according to claim 13, with the additional step:

- Automatic placement of an SMD connector (10).

15. The method according to claim 13 or 14, with the additional step:

- Covering with an insulating layer (38).

16. The method according to any one of claims 13 to 15, comprising the step:

- Reducing the size of the printed circuit board (2) by separating a portion of the printed circuit board (2) parallel to the conductor tracks (14, 16) and / or main recesses (26).