WO2017216411A1

WO2017216411A1 - A circuit board system

Info

Publication number: WO2017216411A1
Application number: PCT/FI2016/050420
Authority: WO
Inventors: Antti Holma; Sauli KUNNAS
Original assignee: Coriant Oy
Priority date: 2016-06-13
Filing date: 2016-06-13
Publication date: 2017-12-21

Abstract

A circuit board system comprises a circuit board (101) and an electrical component (104). The circuit board comprises apertures (102) provided with electrically conductive linings (103) that have galvanic contacts with electrical conductors of the circuit board. The electrical component (104) comprises conductor feet (105) protruding through the apertures. Soldering metal (106) is inside the apertures and in contact with the conductor feet of the electrical component. The circuit board comprises one or more recesses (107) whose bottoms comprise the apertures. As the circuit board is thinner on areas comprising the apertures and thereby the apertures are shorter in the direction perpendicular to the circuit board, it is easier to control a soldering process of the electrical component and to check the quality of the formed solder joints.

Description

A circuit board system

Field of the invention

The disclosure relates generally to solder joints. More particularly, the disclosure relates to a circuit board system that comprises a circuit board and one or more electrical components furnished on the circuit board.

Background

A typical circuit board system comprises a circuit board furnished with electrical components. The circuit board comprises one or more layers of electrically insulat- ing material and electrical conductors on one or both of the surfaces of the circuit board and/or between the layers of the electrically insulating material. Each of the electrical components can be, for example, an integrated circuit such as a processor or a memory, or a discrete component such as a resistor, a capacitor, an inductor, a transistor, or a diode. In many cases, one or more of the electrical com- ponents are through-hole "TH" mounted components which comprise conductor feet that protrude through apertures of the circuit board. Each aperture of the circuit board comprises typically an electrically conductive lining that has galvanic contacts with one or more electrical conductors of the circuit board. The conductor feet of the electrical components are connected to the electrical conductors of the circuit board by soldering so that the apertures are at least partially filled with soldering metal. The soldering can be carried out for example as a wave soldering where a wave of molten solder metal is arranged to sweep the side of the circuit board opposite to the side where of the electrical components are located.

In order to provide a reliable solder joint between a conductor foot of an electrical component and the electrically conductive lining of the respective aperture, a sufficient portion of the room between the conductor foot and the electrically conductive lining has to be filled with soldering metal. In other words, the so called "barrel fill" of each aperture has to reach a pre-determined level. For example, the IPC specifications, e.g. IPC610, require that the barrel fill is at least 75 % or at least 50 % depending on a case under consideration. In this context, the acronym "IPC" means the international trade association for the printed-board and electronics assembly industries.

In modern circuit board systems, a circuit board may comprise many layers and thereby the circuit board can be so thick that it is challenging to control a soldering process of through-hole "TH" mounted components. Furthermore, due to the thickness of the circuit board, it may be challenging to check the quality of the formed solder joints.

Summary

The following presents a simplified summary in order to provide basic understand- ing of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the inven- tion.

In accordance with the invention, there is provided a new circuit board system that can be, for example but not necessarily, a part of a telecommunication device that can be for example an Internet Protocol "IP" router, a Multiprotocol Label Switching "MPLS" switch, a packet optical switch, an Ethernet switch, and/or a software- defined networking "SDN" controlled network element.

A circuit board system according to the invention comprises:

- a circuit board comprising one or more apertures each being provided with an electrically conductive lining having a galvanic contact with one or more electrical conductors of the circuit board, an electrical component comprising one or more conductor feet each protruding through one of the one or more apertures, and soldering metal inside each of the one or more apertures and in contact with the conductor foot protruding through the aperture under consideration. The circuit board comprises one or more recesses so that the one or more apertures are at the bottoms of the one or more recesses. The thickness of the circuit board on each of the one or more recesses is less than the thickness of the circuit board on areas of the circuit board outside the one or more recesses. As the circuit board is thinner on areas comprising the apertures and thereby the apertures are shorter in the direction perpendicular to the circuit board, it is easier to control a soldering process of through-hole mounted components. In many cases, the recesses make it easier to visually inspect the quality of the formed solder joints. Furthermore, as the circuit board is thinner on areas comprising the aper- tures, it is naturally easier to fulfill the barrel fill requirements defined in specifications such as e.g. the IPC610, where the acronym "IPC" means the international trade association for the printed-board and electronics assembly industries.

A number of exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims. Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection with the accompanying drawings. The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality. Brief description of the figures

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figures 1 a and 1 b illustrate a circuit board system according to an exemplifying and non-limiting embodiment of the invention, figure 2 illustrates a circuit board system according to an exemplifying and non- limiting embodiment of the invention, and figure 3 illustrates a circuit board system according to an exemplifying and non- limiting embodiment of the invention.

Description of exemplifying and non-limiting embodiments

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

Figure 1 a shows a schematic section view of a part of a circuit board system according to an exemplifying and non-limiting embodiment of the invention. Figure 1 b shows a bottom view a part of the circuit board system. The section shown in fig- ure 1 a is taken along a line A-A shown in figure 1 b. The section plane is parallel with the xz-plane of a coordinate system 199. It is worth noting that figures 1 a and 1 b are presented in different scales. The circuit board system comprises a circuit board 101 furnished with one or more electrical components. The circuit board 101 comprises layers of electrically insulating material and electrical conductors be- tween the layers of the electrically insulating material. In figure 1 a, one of the electrical conductors of the circuit board 101 is denoted with a reference 1 10. Each electrical component can be, for example, an integrated circuit such as a processor or a memory, or a discrete component such as a resistor, a capacitor, an inductor, a transistor, or a diode. Figure 1 a shows a part of one of the electrical components. This electrical component is denoted with a reference 104. The circuit board 101 comprises apertures each of which is provided with an electrically conductive lining having a galvanic contact with one or more of the electrical conductors of the circuit board. Figure 1 a shows a section view of one of the apertures. This aperture is denoted with a reference 102, and the electrically conduc- tive lining of the aperture 102 is denoted with a reference 103. As illustrated in figure 1 a, the electrical component 104 comprises a conductor foot 105 that protrudes through the aperture 102. In this exemplifying case, the electrical component 104 has a total of ten conductor feet as it is shown in figure 1 b. Each of the apertures of the circuit board 101 contains soldering metal that is in contact with the conductor foot protruding through the aperture under consideration. In figure 1 a, the soldering metal is denoted with a reference 106. Typically the soldering metal is alloy which comprises mainly tin and other metals as smaller shares. The composition of the soldering metal can be for example Sn 96.5 %-Ag 3 %-Cu 0.5 % or Sn 99.3 %-Cu 0.7 %. The circuit board 101 comprises recesses so that the apertures are at the bottoms of the recesses. Figure 1 a shows a section view of one of the recesses. This recess is denoted with a reference 107. The thickness TR of the circuit board on each of the recesses is less than the thickness T of the circuit board on areas of the circuit board outside the recesses. In the exemplifying circuit board system il- lustrated in figures 1 a and 1 b, the bottom of each recess comprises only one of the apertures and, as shown in figure 1 b, neighboring ones of the recesses are separated from each other with isthmuses of the areas outside the recesses. It is, however, also possible that the bottom of a single recess comprises two or more apertures of a circuit board. In the exemplifying case illustrated in figures 1 a and 1 b, the recesses are circular and each recess and the corresponding aperture constitute actually a through-hole which has a first section having a greater diameter and a second section having a smaller diameter. The surface area covered by the recesses is typically less than 10% of the whole surface area of one side of the circuit board. Therefore, the recesses do not constitute a significant limitation to the design of the circuit board system. As illustrated in figure 1 a, the conductor foot 105 can be so short that the tip of the conductor foot is in the recess 107. In other words, the conductor foot 105 does not need to extend below the lower surface of the circuit board 101 . The fact that the conductor foot 105 does not need to extend below the lower surface of the circuit board provides space savings in the direction perpendicular to the circuit board 101 , i.e. in the z-direction of the coordinate system 199. In a circuit board system according to an exemplifying and non-limiting embodiment of the invention, the thickness TR of the circuit board on the recesses is at most 75 % of the thickness T of the circuit board on the areas outside the recesses. In a circuit board system according to an exemplifying and non-limiting embod- iment of the invention, the thickness TR is at most 70 % of the thickness T. In a circuit board system according to an exemplifying and non-limiting embodiment of the invention, the thickness TR is at most 65 % of the thickness T. In a circuit board system according to an exemplifying and non-limiting embodiment of the invention, the thickness TR is at most 60 % of the thickness T. In a circuit board sys- tern according to an exemplifying and non-limiting embodiment of the invention, the thickness TR is at most 55 % of the thickness T. In a circuit board system according to an exemplifying and non-limiting embodiment of the invention, the thickness TR is at most 50 % of the thickness T.

In the exemplifying circuit board system illustrated in figures 1 a and 1 b, the ten re- cesses which are related to the electrical component 104 are on the opposite side of the circuit board 101 with respect to the electrical component 104. It is possible that the circuit board system further comprises another electrical component that is on the same side of the circuit board 101 as the above-mentioned ten recesses and the circuit board 101 comprises recesses related to the other electrical com- ponent on the side of the circuit board on which the electrical component 104 is located.

In the exemplifying circuit board system illustrated in figures 1 a and 1 b, the walls and the bottoms of the recesses comprise electrically conductive linings which are made of the same material as the electrically conductive linings of the apertures and which have galvanic contacts with the electrically conductive linings of the apertures. In figure 1 a, the electrically conductive lining of the wall and the bottom of the recess 107 is denoted with a reference 108. The lining 108 improves the heat conduction into the aperture 102 during a soldering process, and thus the risk of a faulty soldering due to insufficient temperature, i.e. a cold soldering, is reduced. Furthermore, the lining 108 improves the cooling of the electrical component 104 via the conductor foot 105 during operation of the circuit board system. In the exemplifying circuit board system illustrated in figures 1 a and 1 b, areas of the circuit board 101 surrounding the recesses comprise electrically conductive linings which are made of the same material as the electrically conductive linings of the recesses and which are have galvanic contacts with the electrically conductive linings of the recesses. In figure 1 a, the electrically conductive lining of the area surrounding the recess 107 is denoted with a reference 109. The lining 109 further improves the heat conduction into the aperture 102 during a soldering process. Furthermore, the lining 109 improves the cooling of the electrical component 104 via the conductor foot 105 during operation of the circuit board system. Figure 2 shows a schematic section view of a part of a circuit board system according to an exemplifying and non-limiting embodiment of the invention. The section plane is parallel with the xz-plane of a coordinate system 299. The circuit board system comprises a circuit board 201 furnished with one or more electrical components. The circuit board 201 comprises layers of electrically insulating mate- rial and electrical conductors between the layers of the electrically insulating material. In figure 2, one of the electrical conductors of the circuit board 201 is denoted with a reference 210. Figure 2 shows a part of one of the electrical components. This electrical component is denoted with a reference 204. The circuit board 201 comprises apertures each of which is provided with an electrically conductive lin- ing having a galvanic contact with one or more of the electrical conductors of the circuit board 201 . Figure 2 shows a section view of one of the apertures. This aperture is denoted with a reference 202, and the electrically conductive lining of the aperture 202 is denoted with a reference 203.

The electrical component 204 comprises a conductor foot 205 that protrudes through the aperture 202. The aperture 202 contains soldering metal that is in contact with the conductor foot 205. In figure 2, the soldering metal is denoted with a reference 206. The circuit board 201 comprises a recess 207 so that the aperture 202 is at the bottom of the recess 207. The thickness of the circuit board on the recess 207 is less than the thickness of the circuit board on areas neighboring the recess. In the exemplifying circuit board system illustrated in figure 2, the above- mentioned recess 207 is on the same side of the circuit board 201 as the electrical component 204. The wall and the bottom of the recess 207 comprise an electrical- ly conductive lining 208 which is made of the same material as the electrically conductive lining 203 of the aperture 202 and which has a galvanic contact with the electrically conductive lining 203. The area of the circuit board that surrounds the recess 207 comprises an electrically conductive lining 209 which is made of the same material as the electrically conductive lining 208 of the recess 207 and which has a galvanic contact with the electrically conductive lining 208 of the recess 207.

A circuit board system according to an exemplifying and non-limiting embodiment of the invention comprises recesses on both sides of a circuit board so that an ap- erture of the circuit board is at the bottoms of both of the recesses. Thus, a circuit board system according to this exemplifying and non-limiting embodiment of the invention may comprise a first recess such as the recess 107 illustrated in figure 1 a and a second recess such as the recess 207 illustrated in figure 2.

Figure 3 shows a schematic section view of a part of a circuit board system ac- cording to an exemplifying and non-limiting embodiment of the invention. The section plane is parallel with the xz-plane of a coordinate system 399. The circuit board system comprises a circuit board 301 furnished with one or more electrical components. The circuit board 301 comprises layers of electrically insulating material and electrical conductors between the layers of the electrically insulating mate- rial. Figure 3 shows one of the electrical components. This electrical component is denoted with a reference 304. The circuit board 301 comprises apertures each of which is provided with an electrically conductive lining having a galvanic contact with one or more of the electrical conductors of the circuit board. Figure 3 shows section views of two of the apertures. The electrical component 304 comprises conductor feet 305 that protrude through the apertures of the circuit board 301 . The apertures contain soldering metal that is in contact with the conductor feet of the electrical component 304. The circuit board 301 comprises a recess 307 so that the apertures are at the bottom of the recess 307. The thickness of the circuit board on the recess 307 is less than the thickness of the circuit board on areas neighboring the recess. In the exemplifying circuit board system illustrated in figure 3, the above-mentioned recess 307 is on the same side of the circuit board 301 as the electrical component 304 and the electrical component 304 is partly inside the recess 307. The walls and the bottom of the recess 307 comprise electrically conductive linings which are made of the same material as the electrically conductive linings of the apertures. Each electri- cally conductive lining of the recess 307 has a galvanic contact with the electrically conductive lining of one of the apertures. The area of the circuit board that surrounds the recess 307 comprises electrically conductive linings which are made of the same material as the electrically conductive linings of the recess 307. Each electrically conductive lining on the area surrounding the recess 307 has a galvan- ic contact with one of the electrically conductive linings of the recess 307.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated. For example, recesses of the kind men- tioned above may have different shapes when seen along a direction perpendicular to the circuit board. The shape can be, for example but not necessarily, circular, square, rectangle, star-shaped, etc. Furthermore, the spatial shapes of recesses of the kind mentioned above can be such as e.g. cylindrical, conical, etc. Furthermore, a circuit board may comprise grooves connected to one or more re- cesses, e.g. there can be grooves connecting two or more recesses to each other.

Claims

What is claimed is:

1 . A circuit board system comprising:

- a circuit board (101 , 201 , 301 ) comprising one or more apertures (102, 202) each being provided with an electrically conductive lining (103, 203) having a galvanic contact with one or more electrical conductors of the circuit board,

- an electrical component (104, 204, 304) on a first side of the circuit board, the electrical component comprising one or more conductor feet (105, 205) each protruding through one of the one or more apertures, and - soldering metal (106, 206) inside each of the one or more apertures and in contact with the conductor foot protruding through the aperture under consideration, characterized in that the circuit board comprises one or more recesses (107, 207, 307) so that the one or more apertures are at bottoms of the one or more recess- es, a thickness (TR) of the circuit board on each of the one or more recesses being less than the thickness (T) of the circuit board on areas of the circuit board outside the one or more recesses.

2. A circuit board system according to claim 1 , wherein a surface area covered by the one or more recesses is less than 10% of a whole surface area of one side of the circuit board.

3. A circuit board system according to claim 1 or 2, wherein the thickness (TR) of the circuit board on each of the one or more recesses is at most 75 % of the thickness (T) of the circuit board on the areas outside the one or more recesses.

4. A circuit board system according to any of claims 1 -3, wherein the one or more recesses (107) are on a second side of the circuit board, the second side being opposite to the first side of the circuit board.

5. A circuit board system according to any of claims 1 -3, wherein the one or more recesses (207, 307) are on the first side of the circuit board.

6. A circuit board system according to any of claims 1 -5, wherein the bottom of each of the recesses (107, 207) comprises only one of the apertures and neighboring ones of the recesses are separated from each other with isthmuses of the areas outside the one or more recesses.

7. A circuit board system according to any of claims 1 -5, wherein the bottom of at least one of the recesses (307) comprises two or more of the apertures.

8. A circuit board system according to claim 7, wherein the one of the recesses (307) is on the first side of the circuit board and the electrical component (304) is at least partly inside the one of the recesses.

9. A circuit board system according to any of claims 1 -8, wherein the one or more recesses are provided with electrically conductive linings (108, 208) on walls and the bottoms of the one or more recesses, the electrically conductive linings of the recesses being made of same material as the electrically conductive linings of the apertures and having galvanic contacts with the electrically conductive linings of the apertures.

10. A circuit board system according to claim 9, wherein areas of the circuit board surrounding the recesses are provided with electrically conductive linings (109, 209) that are made of same material as the electrically conductive linings of the recesses and that have galvanic contacts with the electrically conductive linings of the recesses.