DE102011087704A1 - Reflow oven for soldering surface mount device (SMD) component on flexible printed circuit board, has tensioning unit that is provided for tensioning the flexible printed circuit board over solder pad - Google Patents

Abstract

The reflow oven (11) has a near infrared (NIR) heater (12) that is provided for irradiating the lower-side of printed circuit board (L). The NIR diaphragm (17,18) is provided below the printed circuit board. A feed device is provided for feeding the printed circuit board in a transport direction (T) over the solder pad (F). A tensioning unit is provided for tensioning the flexible printed circuit board over the solder pad. An independent claim is included for method for soldering components on flexible printed circuit board.

Description

The invention relates to a reflow oven for flexible printed circuit boards, comprising a heating device for heating the at least one printed circuit board on the underside and a feed device for feeding the at least one printed circuit board in a transport direction. The invention further relates to a method for soldering components to at least one flexible printed circuit board in such a reflow oven. The invention is particularly applicable to a placement of SMD modules on flexible circuit carrier and / or for LED light strips.

In reflow soldering or reflow soldering of SMD components onto flexible printed circuit boards, conventional reflow ovens or reflow ovens have been used to provide the heat required for brazing in a continuous operation as convection heat. Alternatively, it is known to bring a flexible circuit board in contact with a heated plate on the underside, so that the heat required for soldering is provided as contact heat. It is disadvantageous, for example, that a soldering profile can not be changed quickly due to a thermal inertness of the heated plate and consequently allows only limited speed of the flexible printed circuit boards through the reflow oven for locally limited soldering operations.

As flexible printed circuit boards, for example, ribbon-shaped flexible printed circuit boards are known, e.g. Type LINEARlight Flex from Osram.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an improved reflow oven for flexible printed circuit boards.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a reflow oven for at least one flexible printed circuit board or circuit carrier, the reflow oven having at least: an IR heating device for irradiating the at least one printed circuit board with infrared (IR) radiation on the underside; at least one provided below the at least one printed circuit board IR shutter for blocking the IR light, which limits a soldering field laterally; a feed device for advancing the at least one printed circuit board in a transport direction over the soldering field; and a tensioning device for tensioning the at least one flexible printed circuit board at least over the soldering field.

By providing the heat necessary for melting or soldering to the at least one flexible printed circuit board in the form of infrared radiation, a heat supply can be increased and decreased comparatively quickly. As a result, the printed circuit board can be locally heated even if it is transported at a high feed rate and / or with discontinuous feed timing. While in conventional reflow / remelting processes, the item to be soldered has to be transported continuously through static heat zones, the present reflow oven makes possible the possibility of the discontinuous feed cycle. This is achieved by the low thermal inertia - both in the heating gradients and in the cooling gradients - of the system so that soldering temperature profiles can be performed on the standing solder. Especially with quasi-endless, flexible printed circuit boards or circuit boards ("Reel-2-Reel-principle"), there is the advantage of a direct connection / chaining with a loading process. In contrast, in conventional, continuously operating reflow / remelt systems, clock equalization would have to be provided, e.g. through a hanging loop. In a hanging loop, however, the components to be melted would "float" after being placed in the viscous solder paste, thereby losing their position. Only the present reflow oven solves this problem.

In addition, the high achievable temperature gradient allows rapid shutdown in a line drop and thus avoiding damage to the flexible circuit board, which reduces a committee.

By means of the reflow oven, one or more flexible printed circuit boards can be soldered simultaneously. The reflow oven can be used in particular for soldering SMD components to the at least one flexible printed circuit board.

The at least one IR diaphragm is thus located at a distance below the at least one printed circuit board or below a correspondingly provided transport plane. Thus, a thermally comparatively slow heat transfer in the form of contact heat from the IR diaphragm is avoided on the at least one circuit board. By means of the at least one IR diaphragm, a laterally clearly defined soldering field is defined, within which the soldering can be carried out, but the thermal secondary radiation to the side is prevented.

It is an embodiment that at least one IR aperture is actively coolable. As a result, heating of the at least one printed circuit board or an environment thereof is performed by at least avoided a diaphragm outgoing heat convection or heat radiation.

It is still an embodiment that at least one IR aperture is movable. Thus, a size of the solder field can be adjusted at least in one direction.

The size of the solder field can be in particular in a range between about 150 mm × 250 mm and about 250 mm × 400 mm, in particular at about 200 mm × 300 mm.

The tensioning device prevents the at least one flexible printed circuit board from sagging (free-hanging) at least due to its heating above the soldering field or from curling on an infrared-transmitting support when guided. Consequently, in particular a flow-through of the solder and / or a non-uniform soldering can be avoided.

It is a further development that the feed device is designed in particular for transporting strip-shaped printed circuit boards, in particular quasi-continuous printed circuit boards, in particular in a roll-to-roll production.

It is still an embodiment that the clamping device in a transport direction of the at least one flexible printed circuit board on the outside of the solder pad each having at least one connected to the IR heater support for supporting the underside at least one flexible printed circuit board; the tensioning device further comprises an abutment associated with a respective support and not connected to the IR heating device for the uppermost support of the at least one flexible printed circuit board (the abutments preferably being arranged further outward with respect to the soldering field); and the IR heater is height adjustable. As a result of this configuration, the supports and associated abutment can be offset in height by simply lifting the IR heating device and the at least one printed circuit board running therebetween can be tensioned. Conversely, the at least one printed circuit board can be relaxed by lowering the IR heater. In this case, a distance of the IR heater does not change to the at least one circuit board, so that the warming of the at least one circuit board is substantially unaffected.

In order to keep the at least one printed circuit board under an at least substantially constant voltage, the IR heating device may be power-adjustable in height, e.g. via a weight-loaded cable pull and / or at least one spring.

The support and / or the abutment can be configured in the form of rollers and / or sliding supports. If a sliding support is provided, this can in particular be angularly adjustable, in particular freely tiltable, in order to enable a conformal sliding of the at least one printed circuit board even under different stress states.

It is also an embodiment that the reflow oven, in particular its tensioning device, in the transport direction tensioned ropes, in particular wire ropes, in particular VA wire ropes, for supporting the at least one circuit board. As a result, sagging can be prevented or suppressed even more effectively, in particular with a comparatively large length of the soldering field or a large length of a free-hanging section of the at least one printed circuit board.

It is also an embodiment that the IR heating device has at least one IR surface radiator. Thus, a particularly uniform heat radiation of at least one circuit board is achieved.

It is also an embodiment that the IR heater has a plurality of mutually parallel, elongated IR emitters. As a result, a locally varying thermal radiation at the soldering field and at the at least one printed circuit board is simplified.

It is a development that a number of IR emitters is between about four and about twenty, especially between six and twelve.

It is still a development that a distance between the elongated IR emitters is between about 300 mm and about 600 mm. As a result, an energy-saving operation with a good localization of the heat radiation and a sufficient power can be combined particularly advantageous.

It is also a development that the elongated IR emitters are round tube emitters, in particular with a diameter between 7 mm and 15 mm. The round tube radiators may in particular have a heatable length of about 200 to about 350 mm. The round tube radiators can in particular have a maximum power of about 0.5 kW to about 2 kW, in particular of about 1 kW.

It is also a development that the elongated IR radiators are aligned in the transport direction, so in particular lie parallel to the transport direction. This makes it possible, in particular, to produce a heat distribution varying over the width of the at least one transported printed circuit board.

It is also a development that the elongate IR radiators are aligned transversely to the transport direction, so in particular are perpendicular to the transport direction. As a result, it is possible, in particular, to produce a heat distribution that is particularly finely adjustable over the length of the at least one transported printed circuit board.

The IR heater can preferably be operated clocked, for example, to adjust a heating power particularly flexible and precise.

It is also an embodiment that the soldering field in the transport direction in a central strip with a reduced power IR is irradiated, in particular with about 80% of a peripheral power. This embodiment makes use of the discovery that a heat accumulation can occur in a central region of the printed circuit board, so that a homogeneous temperature distribution across a width of the at least one printed circuit board can be achieved by means of a centrally reduced heat radiation. Such a configuration is particularly easy to implement with aligned in the transport direction elongated IR emitters.

It is also an embodiment that the IR radiation is a NIR (near-infrared) radiation. This type of radiation causes a particularly effective heating of the at least one circuit board. The NIR radiation may, in particular, have the wavelength ranges between 780 nm and 3 μm and thus comprises, in particular, the spectral ranges IR-A and IR-B.

It is a further development that the at least one printed circuit board at least at the solder pad on at least one infrared transparent cover, in particular glass plate, rests or is guided over spaced. The infrared-transparent cover can thus cover the solder field in both cases. In particular, a glass plate typically transmits IR radiation, so that the glass plate does not hinder rapid heating and cooling of the printed circuit board, but covers the IR heating device in a protective manner. Under a glass plate can be understood in particular a plate made of glass or glass ceramic.

In particular, it is a further development that a distance between the at least one IR heating device or its heat-generating region, in particular IR emitters, is between approximately 40 mm and 80 mm, in particular between approximately 60 mm and 70 mm. This has proved to be a particularly effective distance to the solution of the problem.

It is preferred for a flexible use of the reflow oven with different printed circuit boards further development that the distance is adjustable, in particular in a range of +/- 15 mm.

It is generally possible to provide heat transfer by convection in addition to heat transfer by radiation.

It is also an embodiment that the feed device has at least one movable in the transport direction vacuum mounting means for attachment to a bottom of the at least one flexible printed circuit board. The vacuum fastening device can suck in at a position of the at least one printed circuit board, entrain this in the transport direction and / or push and then release again. A vacuum fastening device allows a residue-free, easy and releasable entrainment or transport of the at least one printed circuit board in the transport direction. The vacuum fastening device may be e.g. as a suction cup or similar be educated.

It is still a further development that the at least one flexible printed circuit board is equipped, at least in its finished state, with at least one semiconductor light source, in particular with at least one light-emitting diode (LED light strip or LED flex strip). It is also a development that the at least one flexible printed circuit board or circuit board in its finished state with at least one SMD component, in particular semiconductor light source, (SMD-) is equipped.

The object is also achieved by a method for melting or soldering components onto at least one flexible printed circuit board in a reflow oven as described above, the method comprising at least the following steps: advancing a region of the at least one flexible printed circuit board to be soldered onto the solder field; and irradiating a bottom of the at least one flexible circuit board on the solder pad by means of the IR heater.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment which will be described in detail in conjunction with the drawings.

1 shows in plan view a reflow oven with a flexible circuit board; and

2 shows the reflow oven 1 as a simplified sectional view in side view.

1 shows in plan view a reflow oven 11 for a flexible printed circuit board L. 2 shows the reflow oven 11 as a sectional view in side view.

The reflow oven 11 has an IR heater 12 on. This includes an open-top, box-like housing 13 in which several oblong NIR emitters 14 are arranged parallel to each other and to a feed direction or transport direction T of the flexible printed circuit board L. The NIR emitters 14 emit infrared light in the near infrared (NIR) range. A distance of the NIR emitters 14 is between 300 mm and 600 mm.

By means of the NIR emitters 14 Consequently, it can have a top opening 15 of the housing 13 guided flexible circuit board L bottom side are irradiated with NIR radiation. Below the NIR emitter 14 there is a radiator cooling 16 ,

At or above the opening 15 There are several IR-stops 17 . 18 for shading the out of the opening 15 upward NIR radiation. The irises 17 define a solder field F from which the NIR radiation exits to heat the flexible circuit board L. The flexible printed circuit board L is therefore heated substantially only above the soldering field F for soldering components located in this region, in particular SMT components (FIG.

The IR irises 17 . 18 for this purpose include a with respect to the circuit board L and the transport direction T left-side panel 17 and a corresponding right-side panel 17 for defining a left or right edge of solder pad F. The apertures 17 can each be fixed or perpendicular to the transport direction T to be installed movable. The IR irises 17 . 18 further comprise a front panel with respect to the circuit board L and the transport direction T 18 . 18a and a corresponding rear panel 18 . 18b for defining a front or rear edge of the solder pad F. Also the apertures 18 can each be fixed or movable installed. That's how the front panel looks like 18 . 18a eg be fixed or movable in the transport direction T, and the rear panel 18 . 18b may be movable in the transport direction T, eg by means of a spindle motor 19 , Consequently, a size of the solder field F can be set specifically. IR radiation can not outside the solder field F, especially not outside the aperture 17 . 18 escape.

At least one of the panels 17 . 18 respectively. 18a . 18b can be actively cooled, eg air-cooled or water-cooled. For example, the apertures 18a . 18b to each coolant connections 21 to the flow of coolant K (water, air, etc.).

The reflow oven 11 also has a feed device 22 for advancing the (at least one) printed circuit board L in the transport direction T via the solder pad F. The feed device 22 has a sliding suction cup 23 as part of a vacuum fixture 24 for selective attachment to an underside of the flexible printed circuit board L. This allows the bottom of the circuit board L to the evacuated suction cup 23 be held and with a procedure of the suction cup 23 be pulled in the transport direction T with. Upon reaching a desired shift, the negative pressure in the suction cup 23 dissolved, the suction cup 23 Move against the transport direction T and placed again on the circuit board L. One for vacuum fastening device 24 associated vacuum generating device, vacuum hoses, etc. are not shown.

The reflow oven 11 also has a tensioning device 25 for tensioning the at least one flexible printed circuit board L at least over the soldering field F. The clamping device 25 has in the transport direction T before and behind the solder pad F with the IR heater 12 connected support in the form of a respective role 26 to the lower side support on the flexible circuit board L. The clamping device 25 Furthermore, in front of or behind the soldering field F, there is one not each with the IR heater 12 connected counter-bearing in the form of a roll 27 to the top-side support on the top of the flexible circuit board L. The IR heater 12 and with it the roles 26 are height adjustable (eg by a maximum of 15 mm) while the rollers 27 not height adjustable. One between the roles 26 . 27 inserted and running therein circuit board L can therefore by a displacement of the IR heater 12 and the roles 26 be stretched upward so that it does not sag or not significantly over the solder pad F. The shift of the IR heater 12 and the roles 26 In particular, force-controlled, for example, by weight via a cable or a spring mechanism, are performed to allow a constant voltage of the circuit board L, even at different temperatures.

Furthermore, especially with a comparatively long soldering field F, ropes may be used 28 be stretched over the solder pad F, which support the circuit board L and further reduce sagging. The ropes 28 can also be tensioned by force.

Before a reflow or reflow process, the circuit board L first likes to roll 26 . 27 be threaded and at least until the suction cup 23 the vacuum fastening device 24 be advanced so that it can cause an automatic feed of the circuit board L in the transport direction T. Subsequently, the circuit board L by means of a displacement of the IR heater 12 and the roles 26 be stretched upwards. A (height) distance between the NIR radiators 14 and the circuit board L is then preferably between about 60 mm and 70 mm.

Following can the NIR emitters 14 be switched on and operated, for example clocked. For reflow or remelting process, the circuit board L is moved over the solder pad F and thereby heated so stably that on a top of the circuit board L located, aufzulötende components, in particular SMT components, such as resistors, light-emitting diodes, etc., are soldered.

Since the printed circuit board L tends to generate heat accumulation in a central region over its width (transversely to the transport direction T), the solder field F is heat-irradiated in the transport direction T in a central direction with a reduced power, in particular with approx 80% of marginal performance. This can be achieved here by the fact that of the six NIR emitters shown here 14 the two middle separate from the outer NIR emitters 14 be operated, with a correspondingly lower performance.

Although not shown in the figures, the reflow oven can 11 be designed for the extraction of the process exhaust gases occurring during the assembly by a regulated exhaust air mass flow or cooperate with a corresponding suction device. The adjustment of the air mass flow improves a reproducibility of the soldering or reflow process.

The reflow oven 11 has the further advantage that the "free hanging" clamped fixation of the flexible printed circuit board L over the IR heater 12 it first makes it possible to solder larger areas in a process without creating bubbles or wrinkles, thereby making it possible to provide more reliable and at the same time more economical production. In contrast, in a known heat transfer by contact (Konduktion) the material to be soldered (often a flexible printed circuit board made of plastic) typically has a much higher thermal expansion coefficient than the heating plate (metal), thereby disadvantageously arise during heating bubbles or wrinkles. These bubbles and / or wrinkles interrupt the heat transfer and the soldering is interrupted locally.

While the invention has been further illustrated and described in detail by the illustrated embodiment, the invention is not so limited and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

That's what the NIR emitters like 14 also be arranged transversely to the transport direction.

Alternatively or additionally, the solder pad F may be from an infrared transparent cover 29 , Eg a glass plate to be covered. The PCB L likes on the cover 29 slide or be spaced apart.

The reflow oven may have other elements, such as devices for hot air extraction, exhaust gas purification, hot air supply, energy supply, control and regulation, etc.

Claims (12)

Reflow oven ( 11 ) for at least one flexible printed circuit board (L), comprising at least: - an IR heating device ( 12 ) for the underside irradiation of the at least one printed circuit board (L); At least one IR diaphragm provided below the at least one printed circuit board (L) ( 17 . 18 . 18a . 18b ), which delimits a soldering field (F) laterally; A feed device ( 22 ) for feeding the at least one printed circuit board (L) in a transport direction (T) via the soldering field (F); and a tensioning device ( 25 ) for tensioning the at least one flexible printed circuit board (L) at least over the soldering field (F). Reflow oven ( 11 ) according to claim 1, wherein at least one IR diaphragm ( 18 . 18a . 18b ) is actively coolable. Reflow oven ( 11 ) according to one of the preceding claims, wherein at least one IR diaphragm ( 17 . 18 . 18a . 18b ) is movable. Reflow oven ( 11 ) according to one of the preceding claims, wherein - the tensioning device ( 25 ) in a transport direction (T) of the at least one flexible printed circuit board (L) on the outside of the solder pad (F) in each case at least one with the IR heater ( 12 ) connected support ( 26 ) for supporting the underside of the at least one flexible printed circuit board (L); - the tensioning device ( 25 ) a respective support ( 26 ), not with the IR heater ( 12 ) connected abutments ( 27 ) to the upper side support of the at least one flexible printed circuit board (L); and - the IR heater ( 12 ) is height adjustable. Reflow oven ( 11 ) according to one of the preceding claims, wherein the reflow oven ( 11 ), in particular the tensioning device ( 25 ), in the transport direction (T) tensioned cables ( 28 ) for supporting the at least one printed circuit board (L). Reflow oven ( 11 ) according to one of the preceding claims, wherein the IR heating device ( 12 ) has at least one IR surface radiator. Reflow oven ( 11 ) according to one of the preceding claims, wherein the IR heating device ( 12 ) a plurality of mutually parallel, elongated IR radiator ( 14 ) having. Reflow oven ( 11 ) according to one of the preceding claims, wherein the soldering field (F) in the transport direction (T) in a central strip with a reduced power IR-irradiated, in particular with about 80% of a peripheral power. Reflow oven ( 11 ) according to any one of the preceding claims, wherein the IR radiation is NIR radiation. Reflow oven ( 11 ) according to one of the preceding claims, wherein the feed device ( 22 ) at least one in the transport direction (T) movable vacuum fastening device ( 23 . 24 ) for attachment to a bottom of the at least one flexible printed circuit board (L). Reflow oven ( 11 ) according to one of the preceding claims, wherein the soldering field (F) by means of an infrared-transparent cover ( 29 ) is covered. Method for soldering components onto at least one flexible printed circuit board (L) in a reflow oven ( 11 ) according to one of the preceding claims, wherein the method comprises at least the following steps: - advancing a region of the at least one flexible printed circuit board (L) to be soldered onto the soldering field (F); Irradiating an underside of the at least one flexible printed circuit board (L) on the soldering field (F) by means of the IR heating device ( 12 ).

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