Printed circuit board with stacked components and method for producing the same

Description

[0001] The invention relates to a printed circuit board, wherein at least one surface of the printed circuit board has solder contacts with components soldered thereon, conductor tracks, and regions that insulate the solder contacts and / or the conductor tracks from each other. A first film serving as a solder resist layer is applied to at least a first portion of the insulating regions, preferably a majority of the insulating regions. Furthermore, the invention relates to a method for producing the printed circuit board according to the invention.

[0002] Many electronic components are available as surface-mounted devices, also known as SMD components. SMD components do not require circuit board holes for assembly, but are soldered directly to the designated terminals with their contacts. SMD components are mechanically placed on contact pads coated with solder paste on the circuit board using automatic placement machines and soldered together in a single reflow process. In addition to SMD components, there are a number of special components that have larger dimensions due to their function. These components are preferably designed as through-hole technology (THT) components. THT components have pin-shaped connecting wires that are inserted through metallized connection holes or vias in the circuit board.THT components are typically soldered using a selective or wave soldering process.

[0003] The solder resist layer primarily serves to protect the conductor tracks from the liquid solder during the soldering of the components' solder contacts to the surface of the circuit board. For the purposes of this application, both the contact surfaces of the SMD components and the through-hole vias of the THT components are referred to as "solder contacts." The solder resist layer prevents the coated areas of the circuit board surface from wetting. This prevents the liquid solder from forming bridges on the insulating areas. In the prior art, the solder resist layer is applied to the unpopulated circuit board during the circuit board manufacturing process.

[0004] Two types of printed circuit boards, each with a uniform solder resist layer, are known in the prior art. This is either a uniform solder resist layer applied as a solder resist, or a uniform solder resist layer applied as a film. Since the solder resist layer is only present in the areas of the circuit board surface that serve as electrical insulation (in short: insulating areas), it must be applied selectively. For a solder resist layer designed as a solder resist, uncured solder resist is first applied over the entire surface of the circuit board. This is then selectively cured in the insulating area, for example using phototechnical methods. The uncured solder resist is then removed from the non-insulating area of the circuit board that is to be exposed (for example, the area of the solder contacts).A foil-formed solder resist layer, on the other hand, is applied by pressing the foil onto the surface of the circuit board, optionally using a joining agent. The foil contains a negative of the area on the circuit board to be exposed. Subsequent removal of the negative, for example, by etching, creates the solder resist layer, selectively applied in the insulating areas and formed as a foil.

[0005] Furthermore, US 2016 / 163613 A1 discloses an encapsulated arrangement of SMD components with THT components arranged on the encapsulation to achieve a space-saving arrangement. IBM TECHNICAL DISCLOSURE BULLETIN Vol. 37, No. 6A, June 1, 1994 (1994-06-01), pages 489 / 490, ISSN: 0018-8689, discloses a roll-to-roll process for providing printed circuit boards with an insulating film. Further examples of encapsulated or stacked components are known from EP 0 727 819 A2, WO 98 / 20713 A1, and DE 10 2007 010731 A1.

[0006] The solder resist layer also determines the electrical resistance of the insulating area coated with it, in short: the insulation resistance. For a given geometry of the solder contacts and / or conductor tracks, the insulation resistance is essentially determined by the material properties of the solder resist layer. The solder resist layer applied as a foil is generally significantly thicker (approximately 80-150 micrometers) than the thickness of the solder resist layer applied as solder resist (approximately 5-40 micrometers). Due to the greater solder resist thickness, higher insulation resistance values can often be achieved with the foil.

[0007] A high insulation resistance, partly determined by the solder mask layer, is particularly necessary if the circuit board is part of an automation field device intended for operation in potentially explosive atmospheres. Explosion protection is achieved here by ensuring that the insulation resistance is above a minimum resistance required by the relevant standards. This prevents short circuits, even in the event of a fault. RF components require a particularly high insulation resistance between their solder contacts. HF is the abbreviation for "high frequency," and RF components refer to components used in high-frequency technology, such as cables, connectors, antennas, transistors, and other components.

[0008] Often, the space available for arranging components on a printed circuit board is severely limited. This is partly due to the fact that, for example, a large number of different components must be placed on the board due to the diverse functionalities of the field device. On the other hand, the available space on the surface of the printed circuit board is further restricted if explosion protection requires the aforementioned minimum distances between components, conductor tracks, and / or solder contacts.

[0009] The invention is therefore based on the object of providing a printed circuit board with a space-saving arrangement of components. Furthermore, the invention is based on the object of providing a method for producing the printed circuit board according to the invention.

[0010] The problem is solved by a printed circuit board, wherein at least one surface of the printed circuit board is provided with solder contacts with components soldered thereon, conductor tracks, and regions that insulate the solder contacts and / or the conductor tracks from one another. A first film serving as a solder resist layer is applied to at least a first portion of the insulating regions, preferably a majority of the insulating regions. At least one of the components is arranged between the printed circuit board and the first film in a direction substantially perpendicular to the surface of the printed circuit board and is at least partially, in particular completely, covered by the first film.

[0011] The circuit board according to the invention advantageously uses the foil serving as a solder resist layer to simultaneously cover at least one component, thereby achieving a space-saving arrangement of the components while simultaneously maintaining the required insulation resistance, which is partly determined by the first foil. In the event that the component is, for example, completely covered by the first foil, the covered component takes up essentially no space on the surface of the circuit board.

[0012] According to the invention, the circuit board has uncovered components, in particular THT or SMD soldered components, whose solder contacts are each adjacent to the first foil serving as a solder resist layer. In this embodiment, the foil serves as a solder resist layer, which adjoins the solder contacts, e.g., by being arranged between the solder contacts of the THT or SMD soldered components.

[0013] In a further embodiment, the component covered by the first film or at least one of the components covered by the first film is arranged in a cavity introduced into the circuit board.

[0014] Preferably, the cavity is dimensioned such that the component covered by the first film is arranged substantially entirely within the cavity. As a result, the film lies substantially completely flat on the circuit board and the covered component.

[0015] In one development, a solder resist serving as a solder resist layer is applied to a second portion of the insulating regions. Alternatively or additionally, a second film serving as a solder resist layer is applied to a third portion of the insulating regions. The solder resist and / or the second film have a solder resist layer thickness that is different from the solder resist layer thickness of the first film covering the at least one component. In this development, solder resist layers of different solder resist thicknesses and, if appropriate, different types of solder resist layers (i.e., solder resist and film) are used on the surface of the printed circuit board. This makes it possible, for example, to match the solder resist layer adjacent to the solder contacts of a component to the specific component. This makes it possible, for example, to set a locally high insulation resistance for the RF components mentioned above via the solder resist layer thickness.

[0016] The covered component is preferably a relatively small component. In a preferred embodiment, the component covered by the first film, or at least one of the components covered by the first film, has a component edge length of less than 5 mm in a direction substantially parallel to the surface of the circuit board or in two directions substantially parallel to the surface of the circuit board. In particular, the component edge length is less than 1 mm and preferably less than 0.5 mm. In a direction substantially perpendicular to the surface of the circuit board, the component has a component height of less than 1 mm. In particular, the component height is less than 0.5 mm and preferably less than 0.3 mm.

[0017] In one embodiment, the component(s) covered by the first foil is / are SMD-soldered. Alternatively, it is possible, for example, to attach the component(s) covered by the foil to the surface of the circuit board using conductive adhesive.

[0018] In a particularly advantageous development, one of the uncovered components is arranged on the side of the first film facing away from the covered component such that the following arrangement results in the direction substantially perpendicular to the surface of the circuit board: circuit board, covered component, first film, uncovered component. The "side of the film" refers to the area extending in the direction of the surface normal on one of the two surfaces of the film. In this development, the covered and uncovered components are arranged directly one above the other in relation to the direction substantially perpendicular to the surface. This allows the space created by covering the covered component to be optimally utilized by the uncovered component arranged directly above it.

[0019] In a preferred embodiment of this further development, the uncovered component has an optical receiving element and the covered component has an optical transmitting element. Alternatively, the uncovered component has an optical transmitting element and the covered component has an optical receiving element. The arrangement or configuration of the transmitting and receiving elements is such that the transmitting element emits optical electromagnetic waves in the direction of the receiving element and that the receiving element receives optical electromagnetic waves coming from the direction of the transmitting element. The covered component, the first film, and the uncovered component form an optocoupler serving for galvanic isolation. Optocouplers known from the prior art are used either as a discrete component with a relatively high space requirement, or can be designed as two separate components with a relatively high space requirement.Therefore, in cases where galvanic isolation is required, this design further significantly reduces the space requirement. Such galvanic isolation is also often required in the explosion protection measures mentioned above.

[0020] With regard to the method, the object is achieved by a method for producing a printed circuit board according to the invention, which comprises at least the following method steps: prefabrication of the bare printed circuit board and, if appropriate, introduction of cavities; arranging, in particular SMD soldering, the at least one component to be covered on the surface of the printed circuit board; subsequent application of the first film serving as a solder resist layer to at least a first portion, preferably a majority of the insulating regions, wherein the at least one component to be covered is at least partially, in particular completely, covered by the first film; and arranging and soldering uncovered SMD and / or THT components on the surface of the printed circuit board, wherein the first film serves as a solder resist layer during the soldering of the SMD and / or THT components.

[0021] The process steps of prefabrication of the circuit board, arranging, in particular SMD soldering, the at least one component to be covered and the subsequent application of the first film serving as a solder resist layer can preferably be carried out by the manufacturer of the circuit board. Subsequently, during further processing of the circuit board, for example by a manufacturer of field devices in which the circuit board is used, the uncovered SMD and / or THT components are arranged on the surface and soldered on. The first film serves as a solder resist layer when the components are soldered on. For example, the covered components are standardized components that are used, for example, in a large number of different field devices. This achieves a high degree of modularization throughout the entire production chain.

[0022] If necessary, a solder resist layer may also be required for soldering the component to be covered, which is arranged between the solder contacts of the component to be covered. In one embodiment of the method, a solder resist layer, in particular a solder resist layer in the form of a solder resist lacquer or foil, is applied between the solder contacts of the component to be covered before the at least one component to be covered is arranged, in particular before the soldering, on the surface of the circuit board.

[0023] In a further embodiment of the method, before arranging and soldering the uncovered components, the solder resist serving as a solder resist layer is applied to a second portion of the insulating regions, and / or the second foil serving as a solder resist layer is applied to a third portion of the insulating regions. The invention is explained in more detail with reference to the following figures, which are not to scale, in which like reference numerals denote like features. Where clarity requires it or it is otherwise expedient, previously mentioned reference numerals have been omitted in the following figures. It shows: Fig. 1 : A sectional view of an embodiment of a printed circuit board according to the invention; Fig. 2 : A sectional view of a further embodiment of a printed circuit board according to the invention; Fig. 3 : A plan view of an embodiment of a printed circuit board according to the invention.

[0024] In Fig. 11 shows a sectional view of a section of an embodiment of a printed circuit board 1 according to the invention, wherein on a surface 11 of the printed circuit board 1, four components 31, 32,... are soldered onto their respective solder contacts 21, 2, ... These are three SMD components 31, 32,... and one THT component 32. The first film 61 is applied to a large part of the insulating areas (not shown here) and serves as a solder resist layer for soldering on the uncovered components 32. Suitable as the first film 61 is, for example, the film sold under the trade name Vacrel ®< in various layer thicknesses of approximately 50-150 micrometers.

[0025] According to the invention, at least one component 31 covered by the first film 61 is arranged on the surface 11 of the circuit board 1. The covered component 31 is arranged and secured before the first film 61 is applied to the surface 11 of the circuit board 1. This preferably takes place at the circuit board manufacturer, who applies the first film 61 as part of the manufacturing process of the circuit board 1. In this exemplary embodiment, the covered component 31 is an SMD-soldered component 31.

[0026] Furthermore, a solder resist layer, here a solder resist 8, is applied locally between the solder contacts 21 of the first component 31. Depending on the type of component and / or design of the solder contacts 21, this solder resist layer can also be omitted if necessary. Of course, the covered component 31 can also be bonded to the surface 11 of the circuit board 1, for example, using circuit board adhesive. The covered component 31 is a chip of size code 0201 according to the EIA standard and thus has a component edge length BL of 0.6 or 0.3 mm. The component height BH is 0.5 mm.

[0027] The uncovered component 32 here is a THT component. The fact that the covered component 31 is covered by the first film 61 makes it possible to arrange the uncovered component 32 directly above the covered component 31, i.e., on the side of the first film 61 facing away from the covered component 31, with respect to the direction RS that is essentially perpendicular to the surface 11 of the printed circuit board. The slight curvature of the first film 61 shown here is not to be considered critical as long as it is ensured that the adhesion properties of the first film 61 on the surface 11 of the printed circuit board 1 are still sufficiently good; this can be assessed, for example, by experimental investigations.

[0028] In Fig. 21 is a sectional view of a section of a further embodiment of a printed circuit board 1 according to the invention, wherein only the covered component 31 and an uncovered component 32 arranged directly above the covered component 31 are shown. Both components 31, 32 are SMD-soldered. The covered component is arranged essentially entirely in a cavity 7; the feature of the cavity 7 can, of course, also be assigned to the Fig. 1 shown embodiment. The cavity 7 enables a substantially planar alignment of the first film, which here has a layer thickness ds of 120 micrometers.

[0029] In this preferred embodiment, the covered component 31 additionally has a receiving diode which serves as a receiving element ED for optical electromagnetic waves. The uncovered component 32 has a transmitting diode which serves as a transmitting element SD for optical electromagnetic waves, i.e. the transmitting element SD and receiving element ED are designed to transmit and receive optical electromagnetic waves, respectively. The diode as the transmitting element SD is a light-emitting diode, and the diode as the receiving element ED is a photodiode. The arrangement of the diodes is such that the transmitting element SD emits optical electromagnetic waves in the direction of the receiving element ED, and that the receiving element ED receives optical electromagnetic waves coming from the direction of the transmitting element SD.The first film 61 is permeable to optical electromagnetic waves from the frequency range in which the optical electromagnetic waves emitted by the LED lie. In this embodiment, the transmitting element SD, the receiving element ED, and the first film 61 form an optocoupler that serves to provide galvanic isolation.

[0030] In Fig. 31 shows a plan view of a section of an embodiment of a printed circuit board according to the invention, wherein the component 31 completely covered by the first film 61 is not visible here. The first film 61, which serves as a solder resist layer, is applied to a large part of the insulating regions 5. For one of the two uncovered components 32,..., a further solder resist layer is provided, which borders the solder contacts 22 of the uncovered component 32. The solder resist layer here is a second film 62, the solder resist layer thickness of which is greater than the solder resist layer thickness ds of the first film 61. For the second uncovered component 32 or its solder contacts 22, the first film 61 covering the covered component 31 is used as the solder resist layer.As a result, in this exemplary embodiment at least two films 61, 62 of different layer thicknesses are used, but if necessary a solder resist can also be used additionally or alternatively. Reference signs and symbols

[0031] 1Printed circuit board 11Surface of the printed circuit board 2Solder contacts 21.Solder contacts of the covered component 31, 32Components 31Covered component 32Uncovered component 4Conductor tracks 5Insulating areas 61First foil 62Second foil 7Cavity 8Solder mask dsLayer thickness of the first foil RSVertical direction BLComponent edge length BHComponent height SDTransmitting element EDReceiving element

Claims

1. printed circuit board (1), wherein solder contacts (2) with components (31, 32,..) soldered thereon, conductor tracks (4) and regions (5) insulating the solder contacts (2) and / or the conductor tracks (4) from one another are provided on at least one surface (11) of the printed circuit board (1), wherein a first foil (61) serving as a solder resist layer is applied to at least a majority of the insulating regions (5), and wherein at least one of the components (31) is arranged between the printed circuit board (1) and the first foil (61) in a direction (RS) substantially perpendicular to the surface (11) of the printed circuit board (1) and is at least partially, in particular completely, covered by the first foil (61), the printed circuit board having at least one uncovered component (32) whose solder contacts (2) are adjoined by the first foil (61) serving as a solder-stop layer, the first foil (61) being arranged between the uncovered component (32) and the printed circuit board (1), and the foil having a thickness of 50 µm to 150 µm.

2. printed circuit board (1) according to claim 1, wherein the component (31) covered by the first foil (61) or at least one of the components (31;...) covered by the first foil (61) is arranged in a cavity (7) provided in the printed circuit board (1).

3. printed circuit board (1) according to at least one of the preceding claims, wherein the cavity (7) is dimensioned such that the component (31) covered by the first foil (61) is arranged substantially completely within the cavity (7).

4. printed circuit board (1) according to at least one of the preceding claims, wherein a solder resist (8) serving as a solder resist layer is applied to a second portion of the insulating regions (5), and / or wherein a second foil (62) serving as a solder resist layer is applied to a third portion of the insulating regions (5), and wherein the solder resist (8) and / or the second foil (62) have a solder resist layer thickness which is different from the solder resist layer thickness (ds) of the first foil (61) covering the at least one component (31).

5. printed circuit board (1) according to at least one of the preceding claims, wherein the component (31) covered by the first film (61) or at least one of the components (31;..) covered by the first film (61) - has, in at least one direction substantially parallel to the surface (11) of the printed circuit board (1), a component edge length (BL) which is less than 5 mm, in particular less than 1 mm and preferably less than 0.7 mm; and - in a direction (RS) substantially perpendicular to the surface (11) of the printed circuit board (1) has a component height (BH) which is less than 1 mm, in particular less than 0.5 mm and preferably less than 0.3 mm.

6. printed circuit board (1) according to at least one of the preceding claims, wherein the component(s) (31;...) covered by the first foil (61) is / are SMD-soldered.

7. printed circuit board (1) according to at least one of the preceding claims, wherein one of the uncovered components (32) is arranged on the side of the first foil (61) facing away from the covered component (31) in such a way that the following arrangement results in the direction (RS) substantially perpendicular to the surface (11) of the printed circuit board (1): - Printed circuit board (1), covered component (31), first foil (61), uncovered component (32).

8. printed circuit board (1) according to at least one of the preceding claims, wherein the uncovered component (32) has an optical receiving element (ED) and the covered component (31) has an optical transmitting element (SD), or wherein the uncovered component (32) has an optical transmitting element (SD) and the covered component (31) has an optical receiving element (ED), the arrangement of the transmitting (SD) and receiving (ED) elements being such, - that the transmitting element (SD) transmits optical electromagnetic waves in the direction of the receiving element (ED) and - that the receiving element (ED) receives optical electromagnetic waves coming from the direction of the transmitting element (SD), and wherein the covered component (31), the first foil (61) and the uncovered component (32) form an optocoupler serving for galvanic isolation.

9. method for manufacturing a printed circuit board (1) according to at least one of claims 1 to 8, wherein the method comprises at least the following method steps, - Prefabrication of the unassembled PCB (1) and insertion of cavities if necessary; - Arrangement, in particular SMD soldering, of the at least one component (31) to be covered on the surface (11) of the printed circuit board (1); - Subsequent application of the first foil (61) serving as a solder resist layer to at least a first portion, preferably a majority, of the insulating regions (5), the at least one component (31) to be covered being at least partially, in particular completely, covered by the first foil (61); and - Arrangement and soldering of uncovered SMD and / or THT components (32, ...) on the surface (11) of the printed circuit board (1), wherein the first foil (61) serves as a solder resist layer during the soldering, wherein the first foil (61) is arranged between the uncovered component (32) and the printed circuit board (1), and wherein the foil has a thickness of 50 µm to 150 µm.

10. method according to claim 9, wherein a solder resist layer is applied between the solder contacts (21) of the component (31) to be covered, in particular a solder resist layer formed as solder resist lacquer or foil, before the arrangement, in particular before the soldering, of the at least one component (31) to be covered on the surface (11) of the printed circuit board (1).

11. method according to at least one of claims 9 or 10, whereby before arranging and soldering the uncovered components (32,...) - the solder resist (8) serving as a solder resist layer is applied to a second portion of the insulating regions (5) and / or - the second foil (62), which serves as a solder resist layer, is applied to a third portion of the insulating areas (5).