EP1486104A2

EP1486104A2 - Method for fitting out and soldering a circuit board, reflow oven and circuit board for said method

Info

Publication number: EP1486104A2
Application number: EP03722340A
Authority: EP
Inventors: Dietmar Birgel
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2002-03-15
Filing date: 2003-03-15
Publication date: 2004-12-15
Also published as: WO2003079743A2; US20050161252A1; DE10211647A1; WO2003079743A3; KR100702544B1; CN100493299C; CN1643999A; KR20040089734A; AU2003229558A1; AU2003229558A8; JP2005521249A; DE10211647B4

Abstract

The invention relates to a method for fitting out and soldering a circuit board which is fitted with a wired electric component with at least one connection wire or pin and a thermally critical housing for conventional automatic soldering methods or a cover. The invention also relates to a reflow oven for soldering the circuit board and a circuit board for the above-mentioned method. The invention makes it possible to solder the thermally critical component in the reflow oven by using the circuit board for thermal shielding of the thermally critical THT components in relation to the thermal energy which is required for the soldering and acts upon the circuit board. The circuit boards (66) are, for example, placed on a frame (67) and transported through the reflow oven (60), whereby the thermally critical components are arranged on the lower side of the circuit boards (66) facing away from the thermal energy.

Description

Process for assembling and soldering a printed circuit board, reflow oven and printed circuit board for such a process

The invention relates to a method for assembling and soldering a circuit board, a reflow oven for soldering the circuit board and a circuit board for the aforementioned method. In particular, the invention relates to such printed circuit boards which are equipped with a wired electrical component with at least one connecting wire or pin and one or a thermally critical housing or casing for conventional automatic soldering processes.

Basically, it should be noted that the aim today is to have the assembly or soldering of printed circuit boards carried out by machine as far as possible in order to optimize manufacturing costs and effort.

The currently best known mechanical soldering methods for soldering electrical and electronic components on a printed circuit board are so-called wave soldering and so-called reflow soldering. These two processes are described in detail in the article by Dr.-Ing. Hans Bell, "Is there a paradigm shift in soldering technology", trade magazine "VTE - STRUCTURE AND CONNECTION TECHNOLOGY IN ELECTRONICS", issue 6 / December 1999, pages 297 to 301. In it, the author describes how and with which components the circuit board is to be assembled according to the individual soldering processes and how the soldering is carried out in detail.

In most of the currently available reflow ovens, a more or less diffuse hot gas stream from pure hot air or a heated special gas is directed vertically onto the surface of the circuit board to be soldered. The circuit boards are heated when entering such a reflow oven and then in the actual work- Transported soldering area. Usual temperatures in the area of the PCB surface to be soldered are up to 220 ° C with dwell times of up to 30 s.

A major problem today when soldering in reflow ovens are those components which do not withstand the thermal conditions in conventional reflow ovens and which are deformed or even destroyed under the conditions prevailing there. For example, connectors, flex connectors, DIP switches or other components, including semiconductor components, with a plastic housing in a commercially available version are not suitable for the usual reflow oven.

In addition, there are other parts or components that are used on printed circuit boards and that are not suitable for soldering in reflow ovens because they include non-heat-resistant parts, adhesives and / or paints.

Such components, which are not resistant to the temperatures prevailing in the reflow oven during the soldering process, cannot participate in the inexpensive mechanical assembly and soldering in reflow oven, but require additional labor-intensive and therefore cost-intensive individual or special assemblies in several special operations.

For some of these components, high-temperature resistant versions are also available, but they are significantly more expensive than the usual components. However, their use is often uneconomical, since they negate the cost savings that are gained by purely mechanical assembly and soldering.

It is therefore an object of the present invention to provide a method for assembling and soldering a printed circuit board, a reflow oven and a printed circuit board for such a process, which also make it possible to provide components which are not resistant to the temperatures prevailing in the reflow oven during the soldering process are to be used in a mechanical soldering process, without the need for complex and costly individual assemblies and / or manual individual soldering.

This object is achieved according to the invention by a first variant of a method for equipping and soldering a printed circuit board with a first and a second side and with at least one wired electrical component (“THT component”) with at least one connecting wire or connecting pin and one or a thermally critical housing or casing for conventional automatic soldering technology, which method comprises the following process steps:

a) On the first side of the circuit board, the THT component is assembled and its connecting wire or connecting pin from the first side through a hole inserted so that it is led out on the second side of the circuit board in the area of a solder contact area printed with a solder paste; and

b) for soldering, the printed circuit board equipped in this way is placed in a reflow oven, the first side equipped with the THT component being at least partially shielded from a heat or energy supply which brings about the soldering.

This object is also achieved according to the invention by a second variant of a method for assembling and soldering a printed circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and one or a thermally critical housing or casing for conventional automatic soldering technology, which method comprises the following process steps:

a) The THT component is fitted on the first side of the printed circuit board and its connecting wire or connecting pin is inserted through a hole from the first side, so that it leads out on the second side of the printed circuit board in the area of a solder contact area printed with a solder paste is; and

b) for soldering, the printed circuit board equipped in this way is placed in a reflow oven, the first side equipped with the THT component being thermally separated from the heat or energy supply acting on the second side of the printed circuit board for soldering, and a temperature difference between them by suitable means the first and the second side of at least 28 ° C is adjustable.

In a preferred embodiment of the method according to the invention, for pasting the second side of the printed circuit board with at least one SMD component, solder paste is provided on soldering contact surfaces provided therefor, and after equipping the second side of the printed circuit board with the SMD component, this together with the connecting wire of the THT -Soldered in one step in the reflow oven.

In another preferred embodiment of the method according to the invention, the first side of the printed circuit board is also equipped with at least one SMD component. A further preferred embodiment of the method according to the invention comprises the following method steps: a) printing solder paste on the first side of the printed circuit board; b) equip the first side with SMD components; c) soldering the SMD components of the first side in the reflow oven; d) equip the first side with at least one THT component; e) printing solder paste on the second page; f) equip the second side with SMD components and g) solder SMD components on the second side and the THT component (s) in the reflow oven.

Further embodiments of the method according to the invention relate to the assembly of connecting wires of the THT components before the solder paste is printed on the second side of the printed circuit board.

Still other embodiments of the method according to the invention relate to fastening THT components on the printed circuit board

Yet another preferred embodiment of the method according to the invention comprises the following method steps: a) printing solder paste on the first page; b) application of adhesive to the locations on the first side to be filled with THT components; c) equip the first side with SMD components; d) equip the first side with THT components; e) soldering the SMD components of the first side in the reflow oven; f) printing solder paste on the second page; g) equip the second side with SMD components and h) solder the components of the second side and the THT components in the reflow oven.

Yet another embodiment of the method according to the invention relates to equipping the printed circuit board with at least one pin-in-hole component (PIH component).

In a further preferred embodiment of the method according to the invention, the first side equipped with the THT component (s) is the The circuit board in the reflow oven is essentially shielded or thermally separated from the heat or energy supply acting on the second side for soldering.

Yet another preferred embodiment of the method according to the invention relates to a horizontal arrangement of the printed circuit board when passing through the reflow oven, the thermally critical THT components to be soldered being located below the printed circuit board.

Yet another preferred embodiment of the method according to the invention is directed to cooling the first side of the printed circuit board in the reflow oven when the second side is soldered.

In another preferred embodiment of the method according to the invention, those areas of the printed circuit board in the reflow oven which, because of a printed circuit board layout, tend to absorb above-average heat energy are covered by a cover which prevents or delays the absorption of heat energy.

In a further preferred embodiment of the method according to the invention, those areas of the circuit board in the reflow oven where above-average absorption of thermal energy is desired are covered by a cover which improves the absorption of thermal energy.

The above-mentioned object is further achieved according to the invention by a first variant of a reflow oven for soldering a printed circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting Pin and one or a thermally critical housing or casing for conventional automatic soldering technology, the first side of the printed circuit board equipped with the THT component being soldered when soldering the second side of the printed circuit board in the area of a connecting wire of the THT component which is printed with a solder paste printed on with solder paste a heat or energy supply causing the soldering is shielded.

The above-mentioned object is also achieved according to the invention by a second variant of a reflow oven for soldering a circuit board with a first one and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and one or a thermally critical housing or casing for conventional automatic soldering technology, the first being equipped with the THT component The side of the printed circuit board when the second side of the printed circuit board is soldered in the region of a connecting wire of the THT component which is led out with a solder paste printed on with solder paste, is separated from a heat or energy supply which brings about the soldering, and a temperature difference between the first and the second side of at least 28 by suitable means ° C is adjustable.

In a preferred embodiment of a reflow oven according to the invention, the side of the printed circuit board equipped with the THT component (s) is essentially shielded or thermally separated by the latter itself in the reflow oven from the heat or energy supply which brings about the soldering.

In another embodiment of the reflow oven according to the invention, a cooling device is provided therein, by means of which the side of the printed circuit board equipped with the THT component or components is cooled during the soldering process.

Yet another embodiment of the reflow oven according to the invention has at least one infrared radiation source which supplies the energy which brings about the soldering.

The above-mentioned object is also achieved by a printed circuit board for one of the above-mentioned methods according to the invention, the printed circuit board being designed or designed in such a way that, with thermal energy acting on the printed circuit board from outside, regions which can be predetermined locally and have above-average thermal energy absorption.

A preferred embodiment of the printed circuit board according to the invention relates to an inner layer of the printed circuit board, which is designed or designed in such a way that a large-area, metallic and / or electrically conductive part is located in the areas of desired above-average heat energy absorption.

The invention is based on the idea of arranging the thermally sensitive components when they pass through the reflow furnace in such a way that they are opposite to the ones towards heat or energy supply acting on the soldering circuit board surface are essentially shielded.

In a preferred embodiment of the invention, the shielding is achieved in the simplest manner by the printed circuit board itself, this effect being supported by additional covers and / or temperature-reducing measures in further preferred embodiments of the invention. In a further embodiment of the invention, the shielding effect of the arrangement of the circuit board according to the invention is also advantageously supported by an appropriately selected design or layout of the circuit board.

The invention is described below using examples of preferred embodiments of the invention and with reference to an accompanying drawing. Show:

Fig. 1 is a schematic representation of various components and

Assemblies on a common circuit board;

2 shows a schematic illustration of another conventional arrangement of different components on a printed circuit board equipped on both sides;

3 shows a schematic representation of a further conventional arrangement of various components on a printed circuit board equipped on both sides;

Fig. 4 is a schematic representation of the sequence of what is common today

Method for assembling and soldering the circuit board according to Fig. 3;

5 shows a schematic illustration of a customary reflow oven;

Fig. 6 is a schematic representation of the sequence of a preferred

Method according to the invention for equipping and soldering components;

Fig. 7 is a schematic representation of a reflow oven according to the invention;

8 shows a schematic illustration of a preferred arrangement of various components on a printed circuit board according to the invention;

9 shows a schematic illustration of a further preferred arrangement of various components on a printed circuit board according to the invention;

10a shows a schematic illustration of a connection point of a

Connection wire of a component according to a conventional assembly and

soldering;

10b shows a schematic representation of a connection point of a

Connection wire of a component after an assembly and soldering process according to the invention; 11 shows a schematic illustration of a further printed circuit board according to the invention during the soldering process with a thermal shield; and

Fig. 12 is a schematic representation of another circuit board according to the invention during the soldering process with a special cover.

For simplification, the same devices, parts or components are provided with the same reference symbols in the drawing.

To illustrate the components used in a conventional printed circuit board and the problems associated with them due to their different thermal resistance, an example of such a printed circuit board 1 is shown schematically in FIG. 1. The following explanations of previously used printed circuit boards, assembly and soldering methods also serve to show the progress and advantages achieved by the invention.

For simplification, the components are not shown as such, but are illustrated by the printed circuit board 1. In addition to components not specified here, there are transformers 2, special plugs 4 with large housings, rotary switches 5 and resistors 6. In addition, angled plugs 7 and semiconductor components in TO housings 8 and in DIL housings 9 are also provided on the printed circuit board 1. The components shown are either wired or those with connecting pins, in which the connecting wires or pins are inserted through metallized bores in the soldered connections of the printed circuit board 1; they are therefore referred to below as "THT components". THT is short for Through Hole Technique. Such THT components are usually soldered in a wave solder bath or, if they do not withstand the temperatures there or deform, manually. As described above, this is a very expensive process.

However, some of the components shown in FIG. 1 can also be so-called PIH components. PIH is short for Pin | n Hole. In the case of such components, the connecting wires or pins are greatly shortened and configured so that they can be inserted into metallized blind holes drilled with solder paste at the soldered connections of the printed circuit board 1. If these PIH components are insensitive to the temperatures and conditions prevailing in a reflow oven, they can stand up there soldered in an upright position, for example - if also fitted on the circuit board - with SMD components.

Another example of a conventional printed circuit board is shown schematically in FIG. 2 as a side view of a section of a printed circuit board. This circuit board

10 is equipped both on its first circuit board side 11 and on its second circuit board side 11. Two THT resistors 13a, 13b are shown as examples, one on each side 11, 12 and a component with a THT-DIL housing 14 and a THT angle plug. As is known, in the case of such a printed circuit board 10, the first side 11 with the resistor 13a, the DIL housing 14 and all others is first from this first side

11 inserted THT components and then soldered in a wave pool, for example. Then the other THT resistor 13b, the angled connector 15 and other THT components of the second side 12 are fitted on the second side and soldered manually. This is also known to be a very expensive process. If a component such as the resistor 13b is arranged in FIG. 2, there is also the disadvantage that at least one of the soldering points of the resistor 13b is covered and cannot be checked.

3 shows yet another printed circuit board 20 which is equipped with SMD and THT components. The cutout shown here is also a printed circuit board 20 equipped on both sides with a first 21 and a second component side 22. Thus, for example on the first side 21 THT resistors 23 and a THT angled connector 24 and first SMD components 25 and second SMD components 26 shown. Third SMD components 27 and fourth SMD components 28 are illustrated on the second side 22 of the printed circuit board 20.

The printed circuit board 20 according to FIG. 3 is produced in a conventional manner in accordance with a method schematically represented by FIG. 4. After applying a solder paste 30, preferably using a printing process, for example a screen printing process, to the first side 21 of the printed circuit board 20 (see FIG. 3), the first SMD components 26 and the second SMD components 27 are assembled. This SMD assembly 31 is usually done automatically by an automatic placement machine and with the help of belted SMD components. After assembly, the circuit board 20 is soldered together with other circuit boards to be soldered in a conventional reflow oven. An example of such a reflow oven is shown in FIG. 5 and will be described below described. After soldering in the reflow oven, the circuit board is turned over and an adhesive application 33 is carried out on its second side 22 at the points where the SMD components 27 and 28 are to be placed. A subsequent assembly 34 of the third and fourth SMD components 27 and 28 is again carried out automatically. After the adhesive has hardened, the THT components and those that cannot be fully automatically assembled are assembled. In the printed circuit board shown in FIG. 3, these are, for example, the THT resistors 23 which are to be soldered on the second side 22.

The so-called exotic components also include those that require special fastening on the circuit board because of their uneven mass distribution, since they cannot be adequately fixed against tilting, for example, by a simple adhesive process. These components must be held in their position by means of snap-in technology or by inserting them into a base or the like on the circuit board until the soldering has been carried out or even beyond. After subsequent fluxing 37, the printed circuit board 20, usually together with other printed circuit boards, is placed in a wave solder bath 38, where the components assembled in step 36 are soldered together with the SMD components 27 and 28; if necessary, the circuit boards become still after wave soldering 38 subjected to an additional cleaning.

Even with this method, which is illustrated in FIG. 4 and is modern compared to the manual soldering method described above, it is necessary for the respective printed circuit board 20 to be equipped with the so-called exotic components, which are completely automatic, the printed circuit board or the printed circuit boards from the actual automatic one To take production line. Such a method, which is common today, is complex and cost-intensive.

To supplement what has just been described, FIG. 5 shows a conventional reflow oven 40, which is briefly explained in comparison with a reflow oven 60 according to the invention described later and shown in FIG. 7. Such a reflow oven 40 essentially comprises a housing 41, which is subdivided into a plurality of chambers 42 in its interior in order to enable better temperature control and convection in the individual chambers 42 and targeted heating and soldering of printed circuit boards 46. Each of the chambers 42 is usually equipped with a heat exchanger and a fan 44 provided, above and below a conveyor belt 45 on which the circuit boards 46 are transported through the reflow oven 40 in the direction of an arrow 47. After leaving the reflow oven 40, cooling fans 48 are often provided, which are used for the targeted cooling of the soldered circuit boards 46 to ambient conditions.

As already described above, the temperature inside is a major problem in conventional reflow ovens, particularly for components whose housings cannot withstand these temperatures for the length of time in the oven. It should be noted here that a temperature of up to 220 ° C. prevails above the conveyor belt 45 in a conventional reflow oven 40, as is shown, for example, in FIG. 5. Such a temperature cannot withstand conventional plastic housings on angled plugs, TO or DIL housings of the THT version (see also FIG. 1) without deforming and thus questioning the functionality of the components.

Fig. 6 is a schematic representation of the sequence of a preferred method according to the invention for assembling and soldering components. With this method it is now possible to solder thermally critical components in the reflow oven. The assembly and soldering of a printed circuit board equipped with SMD and PIH components on both sides is considered in detail (see, for example, FIG. 9). After solder paste printing 50 on a first side of the circuit board, an automatic SMD component assembly 51 is carried out, which is sent to reflow soldering 52 in and through a reflow oven. After the circuit board has cooled, 53 of THT components and other thermally critical components are assembled on the first side of the circuit board. These components have already been described above, in particular in the description text for FIG. 4 under the keyword “exotic components”. These components are assembled on the first side, which means that the connection pins or wires of the THT components are inserted through the corresponding holes and through the printed circuit board so that they protrude on the second side. Heavy exotic components or those with an uneven mass distribution that tend to tip over are either fixed with adhesive or are held in the desired position by means of holders, such as snap-in fasteners. In the case of small or light components, it may also be sufficient to have the respective connecting wires or connecting pins on the other, the second Assemble the side of the circuit board, in particular to bend it so that the components are firmly clamped in their position.

For assembly 54 of the connecting wires or connecting pins of the THT components, the printed circuit board is rotated so that its first side points upwards and the so-called exotic components point downwards, that is to say are arranged below the printed circuit board. If necessary, the connecting wires or connecting pins of the THT components are shortened and / or clinched, i.e. so spread or bent that the THT components do not fall out of the circuit board in their overhead position and are held in their position. By shortening the connecting wires or connecting pins of the THT components, it is also achieved that they protrude only slightly beyond the printed circuit board and thus hinder a subsequent application 55 of the solder paste, preferably by means of printing, on the second side of the printed circuit board. In the case of long protruding connecting wires or connecting pins, there is a risk that they will protrude into the plane of the printing screen required for applying the solder paste or prevent its positioning.

Of course, it is also conceivable for particularly heavy THT components or those with an unfavorable mass distribution to be fixed on the first side of the printed circuit board using adhesive.

After the connection wires or connection pins of the THT components have been assembled, an automatic assembly 56 of SMD components and then of PIH components 57 is carried out on the second side of the printed circuit board. Such PIH components are preferably used which are held by a kind of "wet adhesive force" of the solder paste and for which no additional measures for fixing their position and at the desired location are required. Subsequently, the circuit board which is now populated on the second side is placed in a reflow oven according to the invention, for example one according to FIG. 7, and soldered 58 there.

A reflow oven 60 shown in FIG. 7 comprises a housing 61 which, like the reflow oven 40 shown in FIG. 5, is divided into a plurality of chambers 62. In most chambers 62, heat exchangers 63 and blowers 64 are provided in order to control the heat flow in the reflow oven 60 and thereby to heat the circuit board (s) 66 in a desired manner before the actual soldering process and to apply the energy required for soldering to and on the Bring PCB (s) 66. In contrast to the conventional reflow oven 40 according to FIG. 5, the printed circuit boards 66 are arranged on frames 67 or similar structures on the conveyor belt 65. These frames 67 allow a greater distance between the printed circuit boards 66 than usual to the conveyor belt 65, so that in the case of printed circuit boards 66 in which the first side has relatively bulky THT or other “exotic” and thermally critical components, such as transformers 2, connectors 7 1 and 7 or rotary switches 5 of the printed circuit board according to FIG. 1, the latter, despite their size, can be accommodated between the conveyor belt 65 and printed circuit boards 66. In conventional reflow ovens, the space between the conveyor belt and the printed circuit board is only designed for SMD components; relatively large THT components can only be soldered on the side of the printed circuit board facing the heat energy. Then, as described above, only those THT components can be used whose housings are thermally resistant in the reflow oven. If no such THT components are available or they are disproportionately expensive, the only solution is to solder these components separately, for example manually or in a wave solder bath, which allows spot soldering.

However, the invention also allows THT components with thermally critical housings or other thermally sensitive THT components to be transported through the reflow oven 60 and soldered there. The main idea here is that the second side of the circuit boards 66, ie where soldering is to be carried out, is exposed to the action of the current of thermal energy required for the soldering, while its first side with the THT or other "exotic" and thermal elements thereon critical components to the conveyor belt 65 points. The circuit boards 66 themselves shield the thermally critical components from the thermal energy. In order to achieve this, the printed circuit boards 66 are preferably aligned horizontally, as is shown in the reflow oven 60 in FIG. 7, the second side to be soldered pointing upward to the thermal energy acting on it and the thermally critical components being located below the printed circuit boards 66. The thermally critical components are, so to speak, "overhead" and soldered together with the SMD and PIH components fitted on the second side of the printed circuit boards. Depending on the space in the individual chambers 62 of the reflow oven 60 and on the arrangement of the heat exchangers and fans the printed circuit boards can also be arranged in a different way through the reflow oven if it is ensured that the thermal energy required for soldering is in Desirably meets the side of the circuit board to be soldered and the circuit boards themselves cover the thermally critical components and shield them from the flow of thermal energy. It is conceivable to arrange the heat sources or supply laterally in the reflow oven and to allow them to act from the side on the side of the printed circuit boards to be soldered, with the printed circuit boards 66 being transported through the reflow oven at an incline or even vertically.

In comparison to the reflow oven 40 shown in FIG. 5, the reflow oven 60 shown in FIG. 5 has at least one quartz radiator 68. The quartz radiator (s) 68 allow the temperature prevailing in the chambers 62 used for soldering in the reflow oven 60 to be reduced to a temperature below the temperature required for soldering the components. The quartz emitters provide infrared radiation, which then provides the energy required for soldering as additional energy radiation at the soldering points on the side of the circuit board 66 to be soldered. This measure limits the overall temperature prevailing in the reflow oven 60 both on the side to be soldered and on the opposite side of the printed circuit boards 66, where the thermally critical components are. These components can be shielded even better by the printed circuit boards 66 against the infrared radiation of the quartz emitters 68 used for soldering.

It has been shown that solely in the case of thermally critical components on the first side of the printed circuit board 66 and thus by the printed circuit board 66 itself being arranged thermally separated from the thermal energy required for soldering, a temperature difference between the first and the second side of the printed circuit board from about 28 ° C to about 35 ° C. It is advantageous if the circuit board does not have too much copper on the surface, that is to say conductor tracks.

In the case of many components with a housing which is critical in relation to the temperatures prevailing on the upper side of printed circuit boards during soldering, the above-mentioned temperature difference of 28 ° to 35 ° C. between the first and the second side of the printed circuit board is sufficient to avoid the thermally critical THT To be able to solder components in the reflow oven without the housing or the components themselves being damaged or even destroyed by the temperature. If this temperature difference is not sufficient, it is possible, for example, the blowers 64 and / or heat exchangers 63 arranged below the conveyor belt 65 in the last or the last two output-side chambers 62 in the reflow oven 60 according to FIG. 7 for cooling the lower first side of the printed circuit board 66 and the thermally critical components located thereon. In addition, it is also conceivable to equip the reflow oven according to the invention shown in FIG. 7 in the lower part of the chambers with active cooling elements which actively cool the thermally critical components located on the first, lower side of the printed circuit boards, for example by means of a cooled air flow directed thereon. It is clear that these cooling measures require an efficient thermal separation between the second side of the circuit board to be soldered and its first side. It should be noted, however, that the temperature difference then achieved between the first and the second side of the printed circuit board does not lead to voltages in the printed circuit board which can then destroy them. The infrared radiators 68 described above (see FIG. 7) are particularly suitable for essentially point heating of the printed circuit board at the points to be soldered. They could be used to set the average temperature on the entire second side of the circuit board - whether with no active cooling - in such a way that the temperature difference between the first and second side of the circuit board is just sufficient to avoid damaging the thermally critical components on the first side without dangerous thermal stress affecting the circuit board itself.

8 and 9 are schematic representations of preferred arrangements of various components on a circuit board according to the invention. The drawing shows such a printed circuit board 70 after it has been soldered in a reflow oven, preferably in one according to the invention, for example in a reflow oven 60 according to FIG. 7.

On the first side 71 of the printed circuit boards 70 shown here by way of example, two different SMD components 73a and 73b are fitted, which, for example, as described above, are first soldered in the reflow soldering furnace. The THT resistors 75 then fitted on the first side 71 and a THT angle plug 76 (see FIG. 8) are soldered together in the reflow oven after turning the circuit board and assembling the second side 72 of the circuit board 70 with various SMD components 74a and 74b 8, preferably in the horizontal position of the printed circuit board 70 shown in FIG. 8 itself as a shield the thermally sensitive THT resistors 75 and the angled connector 76 with respect to the thermal energy acting on the second side 72 of the circuit board 70 is used.

It has been shown that the described soldering method according to the invention can also be used for the soldering of thermally critical PIH components. This is illustrated by the circuit board 70 in FIG. 9, in which thermally critical PIH resistors 78 and a PIH angle plug 79 are used instead of the corresponding THT components 75 and 76 according to FIG. 8. However, if the PIH components 78, 79 in FIG. 9 are provided with correspondingly shortened connecting wires or pins for the PIH application, it must be ensured for an "overhead soldering in the reflow oven that they do not fall out of the PIH soldering points when the wet adhesive force the solder paste applied there should not be sufficient to hold the PIH components 78, 79 in an overhead position before soldering, for example, the PIH components 78, 79 can be fixed with adhesive or the PIH blind holes into which the connecting wires or Pins of the PIH components 78, 79 are arranged or spaced apart in the individual PIH components 78, 79 in such a way that the connecting wires or pins of the PIH components 78, 79 must be bent such that they jam the PIH components 78, 79 in the PIH blind holes.

10a and 10b illustrate a particular additional advantage that is achieved with the soldering and assembly method according to the invention when soldering THT components. 10a shows a printed circuit board 80 equipped with a THT component 81, the connecting wire 82 of which has been inserted through a desired metallized feedthrough 83 after it has previously been provided with a solder paste 84. The solder paste 84 which usually rests in a type of drop on the metallized feedthrough 83 and closes it is also pierced and divided when the connecting wire 82 is pushed through the metallized feedthrough 83. A part of the solder paste 84 remains on the upper side of the metallized feedthrough 83, the other part forms a drop or a kind of ball on or at the tip of the connecting wire 82.

In the case of a THT component, which in this case is suitable for soldering in a conventional reflow oven and which is brought into the reflow oven in the position shown in FIG. 10a, that is to say arranged on top of the horizontally oriented printed circuit board, the solder paste 84 softens and flows due to the influence of heat in the Reflow oven, where often the drop or ball of solder paste drips on the tip of the lead wire 82 due to gravity. If the remaining solder paste 84 lying on top of the metallized feedthrough 83 is not sufficient to fill a gap around the connecting wire 82 and in the feedthrough 83 during soldering, a defective soldering point can be assumed.

The great advantage of the soldering and assembly method according to the invention, in which the THT components and in particular the thermally critical THT components are soldered overhead in the reflow oven, can be seen in the result after the soldering shown in FIG. 10b. In the reflow oven, the drops or the ball of solder paste at the tip of the connecting wire 82 (see FIG. 10a) flows back under the influence of gravity into the metallized bushing 83, where it is soldered cleanly and forms a secure soldering point.

11 and 12 show a further embodiment of a printed circuit board 90 according to the invention, specifically during soldering in a reflow oven, preferably a reflow oven according to the invention. 11 and 12, a thermally sensitive, relatively heavy THT component 91 is equipped with connecting wires 94, which, as described above, was fixed on the printed circuit board 90 by adhesive dots 93, i.e. dots made of suitable adhesive the circuit board 90 has been brought into the reflow oven in the horizontal position shown in FIGS. 11 and 12. Without gluing, the relatively heavy THT component 91 would fall off the printed circuit board 90. Adhesives of this type are always advantageous if the THT component 91 cannot be fixed in the desired position by other measures, such as, for example, by clinching the connecting wires 94 and by jamming on the printed circuit board 90. These and other types of fixing such a THT component have already been described above.

In order to achieve a temperature difference between the upper side of the printed circuit board 90, which is directed to a heat energy supply required for soldering, illustrated by arrows 96, and the opposite underside of the printed circuit board, facing away from the heat energy supply, which ensures that the thermally critical components on the Underside are not damaged, according to the invention, as shown in FIGS. 11 and 12, also various Means for cover 98 and 99 are used, which are attached to the top of the circuit board.

There are basically two options for setting the desired temperature difference, which is required to protect the thermally critical components 91 on the underside of the printed circuit board 90. On the one hand, the temperature caused by the thermal energy supply 96 on the upper side of the printed circuit board 90 can be set to the minimum temperature required for soldering the selected solder paste. With the appropriate layout of the circuit board, as described above, temperature differences between the top and bottom of the circuit board 90 of approximately 28 ° C. to 35 ° C. can be achieved solely by the shielding effect of the circuit board itself. Since the soldering temperature has already been set at the lower limit, this is sufficient in some cases to avoid damaging the thermally critical components 91 on the underside of the printed circuit board 90.

If this is not sufficient, there is the possibility of improving the thermal separation between the top and bottom of the printed circuit board 90. And the illustrations of FIGS. 11 and 12 show two examples of covers. In FIG. 11, a mask 98 is schematically shown as an example, with which the "free" locations of the printed circuit board 90 between the connecting wires 94 to be soldered are covered. This essentially limits the absorption of thermal energy to the points to be soldered, and excessive heating of the entire printed circuit board 90 is reduced, so that less thermal energy can be released to the thermally critical component 91 on the lower side of the printed circuit board 90. Such a mask is preferably made of a non-metallic material.

In contrast to this, in the case of the cover 99 shown in FIG. 12, the locations of the printed circuit board 90 that are to be soldered are just covered, ie at the locations of the connecting wires 94, for example. It has been shown in tests that a type of preferably metallic cover 99 of suitable thickness can be used to achieve a type of heat build-up underneath it and therefore to the connecting wires 94 of FIG. 12, which leads to a higher temperature at the soldering points covered in this way is reached when it occurs in the uncovered free areas of the printed circuit board 90. This surprising effect of a local above-average temperature increase on the circuit board enables despite low minimum heat energy supply a reliable soldering of the solder joints, ie the connecting wires 94 with the solder paste 94 of FIG. 12. Also in this way, the average heat energy consumption of the printed circuit board 90 can be reduced overall, so that the one required to protect the thermally critical components 91 is thermal Set the separation and temperature difference between the top and bottom of the circuit board 90.

Claims

claims

1. A method for assembling and soldering a circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and one or a thermally critical housing for conventional automatic soldering technology or wrapping, characterized by the following process steps:

2. A method for assembling and soldering a printed circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and a housing or casing which is thermally critical for conventional automatic soldering technology, characterized by the following process steps:

a) The THT component is fitted on the first side of the printed circuit board and its connecting wire or connecting pin is inserted through a hole from the first side, so that it leads out on the second side of the printed circuit board in the area of a solder contact area printed with a solder paste is; and b) for soldering, the printed circuit board equipped in this way is placed in a reflow oven, the first side equipped with the THT component being thermally separated from the heat or energy supply acting on the second side of the printed circuit board for soldering, and by suitable means a temperature difference between the first and the second side of at least 28 ° C is adjustable.

3. The method according to claim 1 or 2, in which for pasting the second side of the printed circuit board with at least one SMD component, solder paste is provided on the solder contact surfaces provided therefor, and in which after the second side of the circuit board with the SMD component, this is soldered together with the connecting wire of the THT component in one work step in the reflow oven.

4. The method according to any one of claims 1, 2 or 3, in which the first side of the circuit board is equipped with at least one SMD component.

5. The method of claim 4, comprising the steps of: a) printing solder paste on the first side of the circuit board; b) equip the first side with SMD components; c) soldering the SMD components of the first side in the reflow oven; d) equip the first side with at least one THT component; e) printing solder paste on the second page; f) equip the second side with SMD components and g) solder SMD components on the second side and the THT component (s) in the reflow oven.

6. The method according to claim 5, in which connection wires of the THT components are assembled before printing the solder paste onto the second side of the printed circuit board.

7. The method according to claim 6, in which the connecting wires of the THT components are clinched or otherwise bent, for example corrugated, so that they clamp the relevant THT component or components on the printed circuit board.

8. The method according to claim 6, in which the connecting wires are shortened before the THT components are assembled so that they protrude only slightly beyond the printed circuit board after the assembly.

9. The method according to any one of claims 5 to 8, in which, prior to the mounting of the THT components, adhesive is applied to the locations to be fitted to fix the THT components on the printed circuit board.

10. The method according to claim 5, characterized in that at least one fixing aid is provided on the printed circuit board and / or on at least one of the THT components, which fixes the relevant THT component mechanically on the printed circuit board after assembly.

11. The method according to claim 10, characterized in that the fixing aid comprises a snap-in mechanism.

12. The method of claim 4, comprising the steps of: a) printing solder paste on the first page; b) applying adhesive to the locations on the first side to be filled with THT components; c) equip the first side with SMD components; d) equip the first side with THT components; e) soldering the SMD components of the first side in the reflow oven; f) printing solder paste on the second page; g) equip the second side with SMD components and h) solder the components of the second side and the THT components in the reflow oven.

13. The method according to claim 12, in which before the solder paste is printed on the second side, connecting wires of the THT components are assembled in such a way that they do not protrude beyond the printed circuit board surface.

14. The method according to any one of the preceding claims 1 to 13, characterized in that at least one of the sides of the circuit board is equipped with at least one pin-in-hole component (PIH component).

15. The method according to any one of the preceding claims 1 to 14, characterized in that the first side of the printed circuit board equipped with the THT component (s) in the reflow oven essentially through the printed circuit board itself from the heat acting on the second side for soldering. or energy supply is shielded or thermally separated.

16. The method according to claim 15, characterized in that in a substantially horizontal arrangement of the circuit board when passing through the reflow furnace for soldering the THT components or the THT component, these or this are located below the circuit board.

17. The method according to any one of the preceding claims 1 to 16, characterized in that the first side of the printed circuit board equipped with the THT component (s) is cooled in the reflow oven.

18. The method according to any one of the preceding claims 1 to 17, characterized in that in the reflow oven those areas of the circuit board that tend to absorb thermal energy above average due to a circuit board layout are covered by a cover preventing or delaying the absorption of thermal energy.

19. The method according to claim 18, characterized in that the cover consists of a non-metallic material.

20. The method according to any one of the preceding claims 1 to 17, characterized in that for the case where above-average heating is desired in a region of the circuit board by the heat or energy supply effecting the soldering in the reflow oven, this region of the circuit board a cover that improves thermal energy absorption is covered.

21. The method according to claim 20, characterized in that the cover consists of a metallic material.

22. Reflow furnace for soldering a circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and one or a thermally critical housing for conventional automatic soldering technology or casing, characterized in that the first side of the printed circuit board equipped with the THT component, when soldering the connection wire of the THT component led out on the second side of the printed circuit board in the region of a soldering contact area printed with a solder paste, from a heat or energy supply which brings about the soldering is shielded.

23. Reflow furnace for soldering a circuit board with a first and a second side and with at least one wired electrical component ("THT component") with at least one connecting wire or connecting pin and one or a thermally critical housing for conventional automatic soldering technology or sheath, characterized in that the first side of the printed circuit board equipped with the THT component, when soldering the connection wire of the THT component led out on the second side of the printed circuit board in the region of a soldering contact area printed with a solder paste, from one for soldering to the second side of the Circuit board acting heat or energy supply thermally is separated and a temperature difference between the first and the second side of at least 28 ° C. can be set by suitable means.

24. Reflow furnace according to one of claims 22 or 23, characterized in that the printed circuit board is arranged during its transport through the reflow furnace so that the first side of the printed circuit board equipped with the THT component or components essentially through the printed circuit board is shielded or thermally separated even from the heat or energy supply acting on the second side of the circuit board for soldering.

25. Reflow furnace according to one of claims 22 or 23, characterized in that a cooling device is provided therein, by means of which the side of the printed circuit board equipped with the THT component (s) is cooled during the soldering process.

26. Reflow furnace according to one of claims 19 to 21, characterized in that it has at least one infrared radiation source; which provides a heat energy causing the soldering.

27. Printed circuit board for a method according to any one of claims 1 to 17, characterized in that it is designed or designed such that it enables locally predeterminable areas with above-average thermal energy absorption when the thermal energy acts on the printed circuit board from the outside.

28. Printed circuit board according to claim 27, characterized in that an above-average proportion of copper is provided in the areas with the desired above-average heat energy absorption.

29. Printed circuit board for a method according to claim 27, characterized in that it is a multi-layer printed circuit board with at least one inner layer, which is designed or designed such that a large-area, metallic and / or. In each case in the areas of desired above-average thermal energy absorption electrically conductive part is located.

30. Printed circuit board for a method according to one of claims 1 to 17, characterized in that it is designed or designed so that in the Areas where below average heat energy consumption is desired, below average copper content is provided.