Circuit board for mounting electronic components

Abstract

The invention relates to a circuit carrier (12) that has an electrical and / or mechanical function and can accommodate electronic components. The circuit carrier (12) has structures (24) in its edge regions (22), which are designed in particular as vias (28) and / or cylindrical indentations (30) provided with a metallization (32). In the area of ​​the metallized structures (24), which are designed in particular as vias (28) and / or cylindrical indentations (30), at least the metallization (32) is partially removed from the circuit carrier (12) up to a certain proportion (46) of a material thickness (42) of the circuit carrier (12). Furthermore, the invention relates to a method for producing metallurgical connections (14) between a base circuit carrier (10) and another circuit carrier (12).

Description

Technical area

[0001] The invention relates to a circuit carrier that has an electrical and / or mechanical function and can accommodate electronic components, and which includes structures in its edge regions that are provided with a metallization. The invention further relates to a method for producing metallurgical connections between a mounting base and at least one further circuit carrier, while preventing cracking in solder joints that electrically and mechanically connect the circuit carrier and a mounting base. State of the art

[0002] DE 10 2016 105 581 A1 relates to the redirection of solder material to a visually inspectable surface of a circuit carrier. A circuit carrier made of a laminate-like material is disclosed, which has an electrical and / or mechanical function and can accommodate electronic components. Furthermore, a solderable electrical contact is located on a soldering surface of the circuit carrier. A solder flow path is formed on the circuit carrier such that, when the electrical contact is soldered to a mounting base, a portion of the solder material flows along the solder flow path towards a surface of the circuit carrier where the presence and geometry of the solder material can be visually inspected after completion of the solder joint between the mounting base and the electrical contact of the circuit carrier.

[0003] DE 10 2012 112 100 A1 relates to the design of the solderable surfaces of a circuit carrier. The circuit carrier includes structures with a metallization at its edge.

[0004] The circuit carrier can be mounted on a mounting base by applying solder to the metallized surfaces of the mounting base. These metallized surfaces are designed to align geometrically with the metallized structures of the circuit carrier being mounted, ensuring a strong solder bond between the base and the metallized edges of the circuit carrier. For mounting, the circuit carrier is placed onto the metallized surfaces of the base, where solder has been applied. The solder is then melted. This wetting of the metallized surfaces of the mounting base and the metallized edges of the circuit carrier creates a mechanical and electrical connection. Description of the invention

[0005] According to the invention, a circuit carrier is proposed that has an electrical and / or mechanical function and can accommodate electronic components. The circuit carrier has structures provided with partial metallization in its edge regions. In the area of ​​the metallized structures, the metallization is absent on the circuit carrier, at least up to a certain material thickness of the circuit carrier.

[0006] The solution proposed according to the invention can prevent uneven shrinkage or expansion of the circuit carrier during the solidification process of the solder used in the cohesive connection, thereby largely preventing the formation of cavities or the resulting heat cracking within a solder joint.

[0007] Advantageously, the circuit carrier proposed according to the invention is designed such that the structures provided with partial metallization are connected to a contacting material of the substantially horizontally extending anchors in the circuit carrier. This significantly improves the mechanical stability of the circuit carrier, particularly in its edge regions.

[0008] In the circuit carrier proposed according to the invention, the areas of the circuit carrier freed from metallization have a substantially perpendicular course to the surface of the circuit carrier at its connection surfaces.

[0009] Advantageously, the circuit carrier proposed according to the invention can be produced by drilling through holes in a laminate-like, plate-shaped material and subsequently metallizing their surfaces. To achieve partial metallization of the vias across the thickness of the circuit carrier, the applied metallization on the inside of the vias can be partially removed using a slightly larger cutting tool, for example, a drill. After sawing through the laminate-like, plate-shaped material, for example, cylindrical shell-shaped structures are obtained along the surfaces of the circuit carriers separated by sawing, and these structures are only partially metallized with respect to the thickness of the circuit carriers.

[0010] In a further advantageous manner, the circuit carrier proposed according to the invention can be manufactured by drilling blind holes in a laminate-like, plate-shaped material and subsequently metallizing their surfaces. After sawing through the laminate-like, plate-shaped material, structures, for example, cylindrical shell-shaped and only partially metallized with respect to the thickness of the circuit carriers, are produced along the surfaces of the individual circuit carriers.

[0011] In a further advantageous manner, the circuit carrier proposed according to the invention can be manufactured by drilling or milling elongated holes in a laminate-like, plate-shaped material and subsequently metallizing their surfaces. To achieve only partial metallization of the vias across the thickness of the circuit carrier, the applied metallization on the inside of the vias can be partially removed using a milling cutter. After sawing through the laminate-like, plate-shaped material, only partially metallized surfaces result along the surfaces of the circuit carriers separated by the sawing, with respect to the thickness of the circuit carriers.

[0012] Furthermore, the invention relates to a method for producing material-locking connections between a mounting base and a circuit carrier, wherein at least the following method steps are carried out: a) Arranging the mounting base and the circuit carrier one above the other; b) Creating material-to-material connections between the top side of the mounting base and a side edge of a circuit carrier.

[0013] In an advantageous development of the method proposed according to the invention, the material-locking connections are produced as soldered connections according to method step b).

[0014] In the method proposed according to the invention, in addition to the partial removal of the metallization, material of the circuit carrier can also be removed.

[0015] Finally, the invention relates to the use of the circuit carrier in the production of PCB modules (PCB ≙ Printed Circuit Boards) with superimposed circuit carriers to prevent heat cracking. Advantages of the invention

[0016] The circuit carrier proposed according to the invention, or the method proposed according to the invention for producing metallurgical bonds between superimposed circuit carriers, enables the creation of circuit carrier modules (PCB modules, PCB ≙ Printed Circuit Boards) in which the occurrence of heat cracking is excluded. The solution proposed according to the invention significantly reduces stresses occurring in the connection during the solidification or hardening of the metallurgical bond, preferably formed as a solder joint, between superimposed circuit carriers due to the generally uneven shrinkage of the circuit carrier. The solution proposed according to the invention does not involve complete metallization, but only partial metallization in a region of the metallized structures on the circuit carrier. For production, a partially opened, i.e.,By halving the through-hole plating, the metallization can be partially removed through subsequent machining, thus reducing the difference in thermal expansion near the structures compared to previously known solutions. These structures can be indentations, flat structures, or protrusions. Reducing the length of the metallization reduces the uneven thermal expansion of the circuit carrier in the direction of its thickness, thereby significantly lowering the stresses that occur during solidification in the solder material.

[0017] Preferably, the metallization, which is usually made of copper or other highly conductive metallic materials, is removed by subsequent machining, so that in the area of ​​the structures, which may in particular be metallized structures with a semi-open structure, a certain thickness of the material of the metallization layer covering the circuit carrier is removed.

[0018] Furthermore, according to the solution proposed according to the invention, a through-hole (PTH - Plated Through Hole) can be arranged in the edge areas that are in relative proximity to the side edge of the circuit carrier, which increases its mechanical stability in the edge areas of the circuit carrier. Short description of the drawings

[0019] The invention will be described in more detail below with reference to the drawings.

[0020] They show: Fig. 1 a view of a cross-section with a mounting base and a circuit carrier connected above it to the mounting base via a material-bonded connection, Fig. 2. A representation of the material behavior occurring between the circuit carrier and the mounting base as the solder joint cools. Fig. 3 a schematic representation of an uneven shrinkage process, Fig. 4. The representation of a material-bonded connection between the base circuit carrier and the circuit carrier arranged above it. Fig. 5 the schematic representation of a partial material removal in the area of ​​metallization and in the edge area of ​​the circuit carrier and Fig. 6 shows a further embodiment of a connection between a base circuit carrier and a circuit carrier, wherein the edge region of the circuit carrier is mechanically reinforced with a PTH (Plated Through Hole). Embodiments of the invention

[0021] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0022] According to the illustration Fig. A module is to be removed from 1, which has at least one mounting base 10 and a circuit carrier 12 arranged above it. Both components 10, 12 are designed as PCBs (PCB ≙ Printed Circuit Boards), whereby the mounting base 10 can also be of other design, such as ceramic substrates. The two in Fig. 1, the components arranged one above the other in a schematic representation, i.e., the mounting base 10 and the circuit carrier 12, are connected to one another via a material-to-material connection 14, which is preferably designed as a solder connection 16. Solder 18 is used to produce solder connections 16, which changes from a liquid to a solid state when the solder connection 16 cools. Electronic components can be applied to the mounting base 10, or the circuit carrier 12, shown only schematically here, using SMD (Surface Mounted Device) technology, for example.

[0023] The at least one solder joint 16, with which the at least one mounting base 10 and the circuit carrier 12 are electrically connected to each other, has an edge region 22. Several connections are located in the plane of the drawing at the edge region 22. Fig. One series of metallized structures 24 are formed. These can be characterized by a substantially semi-open geometry 26 and are then also referred to as castration holes. The metallized structures 24, for example in semi-open geometry 26, can be cylindrical indentations 30 or the like, cut through and provided with an internally lined metallization 32. Other embodiments include planar metallized structures 24. A characteristic of such structures 24 is a metallization 32 made of an electrically conductive material, preferably copper or a copper-containing mixture or the like.

[0024] The metallization 32 is applied as a layer 34 to the metallized structure 24. The layer 34 is applied in a layer thickness 36. The layer thickness 36 is in the range between approximately 20 µm and approximately 60 µm.

[0025] Due to stresses arising within the material connection 14, which is preferably produced as a solder connection 16, due to uneven thermal expansion behavior, cracks occur which, in the course of crack formation and crack propagation 38, 76, can lead to the interruption of an electrical connection and thus to the impairment of the functionality of such a PCB module.

[0026] According to the representation Fig. Figure 1 further shows that the circuit carrier 12, which is arranged on a top surface 44 of a mounting base 10, is made of a material 40. The material thickness of the material 40 of the circuit carrier 12 is indicated by reference numeral 42.

[0027] According to the character sequence Fig. Figure 2 schematically shows the cooling behavior of the contacting material 48, i.e., the solder 18, from which the metallurgical bond 14 in the form of the solder joint 16 is produced. At the time of production of the metallurgical bond 14 formed as the solder joint 16, the solder 18, i.e., the contacting material 48, has a very high maximum temperature 70°C (Tc). π ). At this point, the solder 18 is liquid and begins to cool. During the transition temperature range 72 resulting from the cooling, individual solidified particles 75 form in the molten solder 18, as can be seen in the figure sequence. Fig. 2 can be extracted at a falling temperature.

[0028] How Fig. 2. As can be further seen, when the melt of the solder 18 cools further at a solidification temperature 74, almost completely solidified solder 18 forms in the form of solidification particles 75. Fig. Figure 2 shows that a cavity 76 forms in the area of ​​the metallization 32, which results from the detachment of the solidification particles 75 from the top surface of the metallization 32 or the contacting material 48. This leads to crack propagation 38.

[0029] Fig. Figure 3 schematically shows a cylindrical indentation 30 with a semi-open geometry 26. The shading or dotting indicates the change in dimensions (shrinkage) of the circuit carrier 12 in the Z-direction, i.e., in the direction of the thickness of the circuit carrier 12, that occurs during cooling from 210°C to 190°C. The dark dotted areas in the region of the semi-open geometry 26 exhibit the smallest change. Due to the arrows emanating from the semi-open geometry 26 (here from the metallization 32), which show different expansion behavior and thus uneven shrinkage 78, the heat cracks shown above occur during the cooling process, as described in Figure 3. Fig. 2 schematically indicated.

[0030] Fig. Figure 4 shows a module according to the current state of the art, which comprises the upper circuit carrier 12, which is materially bonded to the upper surface 44 of the mounting base 10 via the solder joint 16. The solder 18 provides a materially bonded and electrically conductive connection between the contact material 48 of the metallization 32 and the contact material 48 applied to the upper surface 44 of the mounting base 10.

[0031] From the representation according to Fig. As shown in section 4, the circuit carrier 12 has beam-shaped anchors 50 in its edge region 22, extending essentially horizontally into the material 40 of the circuit carrier 12. These serve to improve the mechanical properties of the circuit carrier 12, particularly in its edge region 22.

[0032] Fig. 4 shows that, on a side edge 41 of the material 40 of the circuit carrier 12, the metallization 32 applied here in the region of the semi-open geometry 26 is designed to run continuously along the entire material thickness 42. The metallization 32, which is applied as a layer 34 made of copper or another electrically conductive material, has a layer thickness of 36. This design corresponds to the prior art and not to the design of the disclosed invention.

[0033] At the Fig. In the embodiment of the material-bonded connection 14 shown in Figure 4, preferably implemented as a solder joint 16 made of solder 18, a schematic distribution 80 of the coefficient of thermal expansion (CTE) along the axis of the indentation 30 is established, as shown. Due to the laminate-like structure of the circuit carrier 12, the thermal expansion of the base material is greater than the thermal expansion of the metallization material 32 of the indentation 30. Therefore, the coefficient of thermal expansion of the circuit carrier 12 in the region of the metallization 32 of the indentation 30 is smaller than the thermal expansion at a certain distance from the indentation 30. This is indicated in the schematic distribution of thermal expansion plotted against the distance 80 by the double arrow 82, corresponding to a first difference.

[0034] From the representation according to Fig. 5 shows a subsequent, partial material removal of at least the contacting material 48 of the metallization 32. Depending on the type of production, a removal 66 of the material 40 of the circuit carrier 12 may also be present in the region of the side wall 41 of the circuit carrier 12. This material removal of the material 40 of the circuit carrier 12 is represented by reference numeral 60. In the schematic representation according to Fig. 5. The two materials, i.e., the contacting material 48 of the metallization 32 and the material 40 of the circuit carrier 12, are removed to approximately the same extent, resulting in an exposed area 52. The material removal 60 of both the metallization 32 and the material 40 – as shown in Fig. As shown in section 5, this can be done after complete metallization of a via by machining, for example by "backdrilling". As shown in section 5. Fig. As can be seen from Figure 5, after the partial material removal 60, a slightly recessed side wall 41 of the material 40 of the circuit carrier 12 is radially offset in relation to a remaining part 62 of the total material thickness 42 of the circuit carrier 12. In the illustration according to Fig. 5 is further shown as a remaining anchoring 50, extending essentially in a horizontal direction into the material 40 of the circuit carrier 12.

[0035] Through the in Fig. 5 in the edge region 22 of the circuit carrier 12, exposed by a metallization 32 of the metallized structure 24, an area 52 is created that is also in Fig. 5 schematically indicated reduced second difference 84 of the CTE.

[0036] The resulting difference 80 of the coefficient of thermal expansion (CTE) is significantly smaller in absolute terms compared to the first difference 82 as described in connection with the arrangement according to Fig. 4 is shown.

[0037] With regard to the removed material 60 in the area of ​​the side wall 41 of the circuit carrier 12, it should be noted that this material can either be removed essentially following a vertical path 54, or the material removal 60 of both the contacting material 48 of the metallization 32 and the material removal 60 with respect to the material 40 of the circuit carrier 12 can occur in a conicity 56 (see also the illustration according to Fig. 6).

[0038] Fig. Figure 6 shows another variant of a PCB module. From the illustration according to Fig. 6 shows that, analogous to the representation according to Fig. 5 In the PCB module shown here, the circuit carrier 12, on which a number of electronic components not shown in detail here can be arranged, is materially bonded and thus electrically conductive via the solder connection 14, designed as a solder connection 16, to the contacting material 48 on the top side 44 of the base circuit carrier 10 by means of the solder 18. In contrast to the Fig. In the embodiment shown in Figure 5, the material 40 of the circuit carrier 12 arranged above is traversed by a PTH 86 (Plated Through Hole). By arranging this PTH within the edge region 22 of the circuit carrier 12, the mechanical stability of the circuit carrier 12 is improved. From the illustration according to Fig. It follows from Figure 6 that between the material of the plated through hole 86 and the metallization 32 at the outer edge, i.e., at the side wall 41, of the material 40 of the circuit carrier 12, the metallization 32, made of copper or another electrically conductive material, extends as a layer 34 with a layer thickness 36. Between the layer 34, the metallization 32, and the material of the plated through hole 86, individual connecting webs 88 run essentially in a horizontal direction. Of these, [the following are shown in the illustration according to the diagram]. Fig. 6 only two are shown superimposed.

[0039] From the representation according to Fig. Figure 6 further shows that the exposed area 52 is also depicted here, which is created at least by the partial removal of the contacting material 48 of the metallization 32. In the representation according to Fig. Figure 6 shows additionally partially removed material 60 of the circuit carrier 12. The exposed area 52 extends analogously to the illustration according to Fig. 5 in a specific thickness 46, for example, a thickness of 50%, relative to the material thickness 42 of the circuit carrier 12. The remaining part 62 extends over the entire material thickness 42 of the material 40 of the circuit carrier 12 minus the thickness 46 of the exposed area 52. Here, too, depending on the manufacturing process, a radial offset may occur between the new side edge 41 of the material 40 obtained after machining and the layer 34 of the metallization 32. A chamfer 64 is created according to the machining process.

[0040] The invention further relates to a method for producing integral connections 14 between a mounting base 10 and a further circuit carrier 12 arranged above it. Both the mounting base 10 and the circuit carrier 12 are designed as PCBs (PCBs). The method proposed according to the invention involves the following process steps: a) Arranging the mounting base 10 and the circuit carrier 12 one above the other; b) Creating material-bonded connections between the top of the mounting base 10 and a side edge 41 of a circuit carrier 12.

[0041] In the method proposed according to the invention, the materially bonded connections 14 are preferably produced as solder connections 16 from a solder 18 according to process step b).

[0042] The area 52 exposed on the side wall 41 of the material 40 of the circuit carrier 12 by means of the method proposed according to the invention improves the thermal expansion behavior of the materials 40 and 18, 48 respectively, in such a way that excessively high stresses are avoided, so that cracks 76 and crack propagation 38 cannot occur in the first place.

[0043] Furthermore, the invention relates to the use of the circuit carrier 12 in the production of PCB modules (PCB ≙ Printed Circuit Boards) with superimposed circuit carriers 10, 12 to prevent heat cracking.

[0044] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of one skilled in the art. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 105 581 A1

[0002] DE 10 2012 112 100 A1

[0003]

Claims

[1] Circuit carrier (12) for receiving electronic components, which has metallized structures (24) in its edge regions (22), in particular cylindrical indentations (30) lined with a metallization (32), characterized by that on the circuit carrier (12) in the region of the structures (24), in particular the cylindrical indentations (30), at least the metallization (32) is partially removed at least up to a certain thickness (46) of a material thickness (42) of the circuit carrier (12). [2] Circuit carrier (12) according to claim 1, characterized by that in the edge regions (22) of the circuit carrier (12) in addition to the metallization (32) of the structures (24) the material (40) of the circuit carrier (12) is partially removed. [3] Circuit carrier (12) according to claims 1 to 2, characterized bythat the metallization (32) extends horizontally into the material (40) of the circuit carrier (12) via anchors (50) in order to improve the mechanical strength. [4] Circuit carrier (12) according to claims 1 to 3, characterized by that cylindrical indentations (30) and / or vias (28) and / or PTHs (86) (Plated Through Holes) run in the edge regions (22) of the circuit carrier (12). [5] Circuit carrier (12) according to claims 1 to 4, characterized by in that the metallization (32) of vias (28) and / or cylindrical indentations (30) running in the edge regions (22) is connected to a contacting material (48) of the anchoring (50) which is essentially beam-shaped and extends in the horizontal direction. [6] Circuit carrier (12) according to claims 1 to 5, characterized bythat due to the partial material removal (66) of at least the metallization (32), exposed regions (52) of the circuit carrier (12) have a substantially vertical course (54). [7] Circuit carrier (12) according to claims 1 to 6, characterized by that due to the partial material removal (66) of at least the metallization (32), exposed regions (52) of the circuit carrier (12) essentially have a conicity (56). [8] Circuit carrier (12) according to one of claims 1 to 7, characterized by that the region (52) exposed by the partial material removal (66) of at least the metallization (32) is radially offset from the metallization (32). [9] Circuit carrier (12) according to one of claims 1 to 8, characterized by that a bevel (64) is formed on the remaining part (62) of at least the metallization (32) by the partial material removal (66). [10] Method for producing a material connection (14) between a base circuit carrier (10) and a circuit carrier (12) according to one of claims 1 to 9, with at least the following method steps: a) arranging the base circuit carrier (10) and the circuit carrier (12) one above the other; b) producing material-locking connections (14) between the upper side (44) of the base circuit carrier (10) and a side edge (41) of the circuit carrier (12) in the region of the structures (24). [11] Method according to claim 10, characterized by that a solder connection (16) is produced according to method step b). [12] Use of the circuit carrier (12) according to one of claims 1 to 9 in the manufacture of PCB modules (PCB ≙ Printed Circuit Boards) with superimposed circuit carriers (10, 12) to prevent heat cracking.

Images