Method for detecting coating layer of printed circuit board of field device of process and automation technology

Abstract

The invention relates to a method for detecting the layering of at least one coating (1) of a printed circuit board (2) of a field device (3) of process and automation technology for determining and / or monitoring at least one chemical and / or physical parameter of a medium (4), the printed circuit board (2) having a first region (5) with the at least one coating (1), at least one heat-conducting component (6) is arranged in the region of the at least one coating (1), at least one indicating section (7) having the at least one coating (1) and the at least one heat-conducting component (6) is arranged on the circuit board (2), the method comprising at least the following steps: placing the circuit board (2) in a furnace (8) and carrying out at least one heating process; after the at least one heating process, checking the at least one indication section (7) in a layered manner; it is determined whether layering occurs in the at least one indication section (7) during the at least one heating process.

Description

Technical Field

[0001] The invention relates to a method for detecting at least one coating delamination of a circuit board of a field device for process and automation technology, the field device being used to determine and / or monitor at least one chemical and / or physical parameter of a medium, wherein the circuit board has a first area with at least one coating, wherein at least one heat-conducting component is arranged in the area of ​​the at least one coating, wherein at least one indication section having at least one coating and at least one heat-conducting component is arranged on the circuit board. Background Art

[0002] Field devices in process and automation technology are used to monitor and / or determine at least one process variable of a medium, for example a chemical or physical variable. In the context of this application, field devices are generally referred to as all measuring instruments that are used close to the process and provide or process process-related information. The companies of the Endress + Hauser Group produce and sell a wide range of such field devices.

[0003] The process parameter to be determined by the field device can be the level, flow, pressure, temperature, pH value, redox potential or conductivity of the corresponding medium. The different measurement principles that may be used to determine the process parameters are well known in the art and will not be described in detail here. The field device for measuring the level is particularly designed as a microwave level meter, an ultrasonic level meter, a time domain reflectometry level meter (TDR), a radiation level meter, a capacitive level meter, a conductive level meter and a vibrating rod level meter. On the other hand, the field device for measuring the flow works according to measurement principles such as Coriolis, ultrasonic, eddy current, thermal and / or magnetic induction. The pressure measuring instrument is preferably a so-called absolute pressure gauge, a relative pressure gauge or a differential pressure gauge. In addition to the above-mentioned measuring instruments and actuators, the field device also includes remote I / O, a radio adapter or other equipment deployed at the field level.

[0004] A field device generally comprises a sensor which at least partially and / or at least intermittently contacts the process and an electronics unit for, for example, collecting signals, evaluating signals and / or feeding signals. The electronics unit of a field device is generally arranged in a housing and is additionally provided with at least one docking element for docking the electronics unit to the sensor and / or external unit and for transmitting data and / or energy. The docking element can be any connection, even a wireless connection. The electronics unit and the sensor of the field device can be designed as separate units with separate housings or as a common unit with one housing. In general, a field device has at least one circuit board on which components are arranged.

[0005] Circuit boards consist of an electrically insulating material and electrically conductive connections attached to it, which are usually made of copper. Multilayer circuit boards have electrically conductive connections on both sides of the circuit board. To produce a multilayer circuit board, for example, two circuit boards can be bonded to one another using so-called prepregs. Prepregs are semi-finished products made of textile fiber matrices that have been pre-impregnated with reactive resins and cured under temperature and pressure to form a multilayer circuit board. This makes it possible to combine different properties of circuit boards: for example, one section of the circuit board can be a relatively thick rigid circuit board, while another section of the circuit board to which the rigid circuit board is bonded can be a flexible circuit board. The result is a rigid-flex circuit board with rigid and flexible areas. Flexible circuit boards are often based on polyimide films, on which electrically conductive structures are applied.

[0006] Circuit boards usually go through at least one heating step. During this step, delamination (i.e. the coating peels off) can occasionally occur on the board, which means that the board (and often the batch to which it belongs) must be scrapped. Summary of the invention

[0007] In view of the above, an object of the present invention is to provide a method by which waste caused by delamination of circuit boards can be reduced.

[0008] In order to achieve the above-mentioned object, the present invention proposes a method for identifying at least one coating delamination of a circuit board of a field device for process and automation technology, the field device being used for determining and / or monitoring at least one chemical and / or physical parameter of a medium, wherein the circuit board has a first area with at least one coating, wherein at least one heat-conducting component is arranged in the area of ​​the at least one coating, wherein at least one indicator section having at least one coating and at least one heat-conducting component is arranged on the circuit board, wherein the method comprises at least the following steps:

[0009] - placing the circuit board in an oven and subjecting it to at least one heating step;

[0010] - after at least one heating step, at least one indicator section is checked for delamination;

[0011] - determining whether delamination occurs in at least one indicating section during at least one heating process.

[0012] The basic idea of ​​the invention is that delamination occurs more strongly when there is still residual moisture in the circuit board, especially when heat-conducting components are present in the coating area. The indicator section according to the invention enables early detection of delamination. The term "delamination" includes both partial and complete detachment of the coating from the layer adjacent to the coating.

[0013] The indicator section has the same at least one thermally conductive component and at least one coating which are also arranged in the first area of ​​the circuit board. The indicator section can represent the first area of ​​the circuit board or correspond in whole or in part to the first area of ​​the circuit board, wherein at least the at least one coating and the at least one thermally conductive component are provided. For example, the indicator section can occupy 4 mm 2 Up to 5 mm 2 In this way, based on the indicator section, it can be identified whether at least one coating layer is delaminated. Thereby, the indicator section is used as a test sample for delamination of at least one coating layer. Preferably, the indicator section is arranged outside the first area of ​​the circuit board.

[0014] When the circuit board is placed in the furnace and subjected to at least one heating step, heat is introduced into the region of the at least one coating by means of the at least one heat-conducting component. If too much moisture remains in the region of the at least one coating, the water and / or solvent evaporates when heated, causing the at least one coating to detach from the circuit board layer adjacent to the at least one coating. After the heating step, only the indicating section needs to be checked for delamination, since the test result can be extended to the first region of the circuit board. The at least one coating is in particular an inner layer of the circuit board, and is not arranged on the surface of the circuit board.

[0015] If the determination indicates that the section does not delaminate, it is inferred that the first area of ​​the circuit board does not delaminate. On the contrary, if the determination indicates that the section has delaminated, it is inferred that the first area of ​​the circuit board has also delaminated, and further inferred that the circuit board is affected. In addition, it can be inferred that the batch to which the tested circuit board belongs is prone to delamination. Appropriate measures can then be taken, such as removing the batch or performing a drying process on the circuit boards in the batch.

[0016] In one configuration, at least one heat conducting component includes metal.

[0017] In particular, at least one heat conducting component comprises copper.

[0018] In another configuration, at least one heat conducting component has at least one copper layer and / or at least one metallized through-hole.

[0019] Preferably, at least one indicator section is checked for delamination by topological measurement. Delamination of at least one coating may cause a curvature of at least one coating or a curvature of one of the layers adjacent to at least one coating. In the region of the delaminated coating, the circuit board is not flat. This curvature is detected based on the topological measurement.

[0020] Advantageously, the at least one indicator section is checked for delamination by optical inspection.The optical inspection may comprise a topological measurement.

[0021] In particular, the optical inspection is performed during an automated optical inspection. During an automated optical inspection (AOI), components, for example component solder joints, are checked by image processing methods. The method can also be used to detect at least one coating delamination. Typically, the automated optical inspection is performed after the components have been soldered to the circuit board.

[0022] In a further development, at least one indicator section is arranged on a process edge of the circuit board. The process edge is to be removed from the circuit board later. In this way, the at least one indicator section does not take up any space on the circuit board.

[0023] In another refinement, the oven is a reflow oven.

[0024] In one embodiment, the circuit board is printed with solder paste before being placed in the furnace. The solder paste can be remelted in the furnace to form a deposited solder, or the solder paste can be melted so that one or more components are soldered to the circuit board. The detection of delamination of at least one coating can be integrated into the soldering process in order to check whether delamination of at least one coating has occurred after the soldering process.

[0025] In another embodiment, the circuit board is equipped with components before being placed in the furnace. During the heating process, the components are soldered to the circuit board in the furnace. After the heating process, it can be checked whether at least one coating has delaminated.

[0026] Preferably, the first three steps of the method are repeated after a specified time in order to determine whether delamination occurs in at least one indication section after a specified time. These specified times can be coordinated with the process steps of the circuit board. For example, the first three steps of the method can be performed respectively after a specified process step of the first soldering process, the second soldering process, etc. It is possible that delamination does not occur after the heating process of the first soldering process, but only after the heating process of the second soldering process, because, for example, the temperature in the first soldering process is not high enough to cause delamination.

[0027] In one embodiment, at least one coating is designed to absorb or retain moisture.

[0028] In another embodiment, at least one coating layer comprises polyimide. As mentioned above, polyimide can absorb or lock moisture, which can cause at least one coating layer to delaminate under the action of heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In conjunction with the accompanying drawings Figures 1 to 5 The present invention is described in detail. In the figure:

[0030] Figure 1 A schematic diagram of a field device having a circuit board is shown.

[0031] Figure 2 A structural schematic diagram of a rigid-flexible circuit board is shown.

[0032] Figure 3 A schematic structural diagram of a layered rigid-flexible circuit board is shown.

[0033] Figure 4 A schematic diagram of a circuit board with indicator sections is shown.

[0034] Figure 5 Another design of a circuit board with an indication section is shown. DETAILED DESCRIPTION

[0035] Figure 1 A schematic diagram of an exemplary field device 3 is shown. For example, the field device 3 is arranged at a container 14 (such as a tank or a pipe) containing a medium 4, and includes a sensor unit 15 and an electronics unit 16. The sensor unit 15 protrudes into the medium 4 and is connected to the electronics unit 16 via a circuit board 2. The circuit board 2 can also be a part of the electronics unit 16 and / or the sensor unit 15.

[0036] Figure 2 A typical cross section of a rigid-flex circuit board 2 is shown. The polyimide layer 19 is represented in white, the copper layer 9 is represented in black, the prepreg layer 21 is represented in black and white stripes, the core 20 of the rigid section of the circuit board 2 is represented in squares, and the solder mask layer 22 is represented in dots. The flexible section 23 of the circuit board 2 consists of the top three layers, namely two polyimide layers 19 and one copper layer 9. Optionally, the top polyimide layer 19 may include a solder mask layer 22 (not shown). The remaining layers represent the rigid section 24 of the circuit board 2. Figure 2 Only a fragment of the rigid-flex circuit board 2 is shown.

[0037] The core 20 is usually made of a composite material such as FR4. Two copper layers 9 are arranged adjacent to the core 20 and are responsible for the electrical conductivity within the circuit board 2. At least one layer consisting of prepreg 21 is usually applied between the copper layers 9. At the transition between the rigid section 24 and the flexible section 23, the polyimide layer 19 and the prepreg layer 21 are connected to each other, in particular bonded to each other. At this transition, heat input can cause delamination of the polyimide layer 19 and the prepreg layer 21, resulting in the polyimide layer 19 detaching from or warping the prepreg layer 21. The heat-conducting copper layer 9 promotes heat input in particular. Even a single copper layer 9 can already cause heat input and thus delamination. Delamination appears as a visible camber on the circuit board 2, which can be detected by topological measurements (for example in automatic optical inspection) if necessary.

[0038] Figure 3 An example of this layering is shown in Figure 3In the example, at the interface between the flexible section 23 and the rigid section 24, the polyimide layer 19 is separated from the prepreg layer 21, which causes the layer of the flexible section 23 of the circuit board 2 to be cambered. Depending on the size of the camber, it may be visible to the naked eye or it may not be noticeable. Since the circuit board 2 is usually welded to a series of components, the camber may be blocked (partially blocked) by the components, so the camber cannot be seen. In this case, the indicator section 7 can be arranged on the circuit board 2 away from the electronic circuit 25, or even on the process edge 11. Even if the circuit board 2 has been welded to the components, the delamination can be checked based on the indicator section 7, because advantageously no components are arranged in the indicator section 7.

[0039] Figure 4 A schematic diagram of a circuit board 2 with two exemplary indicator sections 7 is shown. The circuit board 2 comprises an area for an electronic circuit 25 and a technical edge 11. In the area of ​​the electronic circuit 25, a plurality of components 13 are soldered to the circuit board 2. In addition, a plurality of metallized through-holes 10 are arranged in the circuit board, which are used for soldering other components and consist of copper, for example. The first area 5 of the circuit board 2 comprises at least at least one coating 1 (not explicitly shown here) and a heat-conducting component 6, which in the present example is shown in the form of a metallized through-hole 10. Alternatively or additionally, the first area 5 can have further heat-conducting components 6, for example one or more copper layers 9.

[0040] After the component 13 is soldered through the metallized through hole 10, the metallized through hole 10 and the first area 5 are substantially covered by the component, so that delamination may not be recognized. For this reason, the indicator section 7, which also has at least one coating 1 and a heat-conducting component 6, can be arranged at a position away from the electronic circuit 25, that is, on the free area of ​​the circuit board 2 or on the process edge 11. Preferably, no component 13 is soldered in the indicator section 7.

[0041] Figure 5 Another design of a circuit board 2 is shown. The figure shows a transverse section through a circuit board 2, which has at least one coating 1, a metallized through hole 10 and a copper layer 9 in a first area. The indicator section 7 also has at least one coating 1 and a metallized through hole 10. However, compared to the first area 5, the indicator section 7 has not only one copper layer 9, but two copper layers 9. By increasing the number and / or volume of heat-conducting components 6 in the indicator section 7 relative to the first area 5, the indicator section 7 is more sensitive to heat input and delamination phenomena than the first area 5. This has the advantage that even slight delamination can be detected using the method according to the invention.

[0042] For example, Figure 5, a plurality of pads 26 are shown, on which solder paste 12 is printed. In the example shown, the circuit board 2 is placed in an oven 8, where a heating process is performed. For example, the solder paste 12 is remelted, and components 13 are arranged on the circuit board 2 after remelting, and are soldered to these components in a second heating process.

[0043] Reference numerals list

[0044] 1 coating

[0045] 2 Circuit Board

[0046] 3. On-site equipment

[0047] 4 Medium

[0048] 5First Area

[0049] 6Heat-conducting components

[0050] 7 Indicator section

[0051] 8 furnaces

[0052] 9 copper layers

[0053] 10 metallized through holes

[0054] 11. Craft edge

[0055] 12. Solder paste

[0056] 13 Components

[0057] 14 Container

[0058] 15 sensor units

[0059] 16 Electronics Unit

[0060] 19Polyimide layer

[0061] 20 Rigid circuit board core

[0062] 21 Prepreg

[0063] 22 solder mask

[0064] 23 Flexible section of circuit board

[0065] 24 Rigid section of the circuit board

[0066] 25 Electronic Circuits

[0067] 26 pads

Claims

1. Method for detecting delamination of at least one coating (1) of a circuit board (2) of a field device (3) for process and automation technology, the field device being used for determining and / or monitoring at least one chemical and / or physical parameter of a medium (4), in, The circuit board (2) has a first area (5) with at least one coating (1), wherein at least one heat-conducting component (6) is arranged in the area of ​​the at least one coating (1), wherein at least one indication section (7) having at least one coating (1) and at least one heat-conducting component (6) is arranged on the circuit board (2), wherein the method comprises at least the following steps: - placing the circuit board (2) into a furnace (8) and performing at least one heating process; - after said at least one heating step, checking said at least one indicator section (7) for delamination; - determining whether delamination occurs in at least one indication section (7) during the at least one heating process.

2. The method according to claim 1, in, The at least one heat conducting component (6) comprises metal.

3. The method according to any one of claims 1 to 2, in, The at least one heat conducting component (6) comprises copper.

4. The method according to any one of claims 1 to 3, in, The at least one heat conducting component (6) has at least one copper layer (9) and / or at least one metallized through-hole (10).

5. The method according to any one of claims 1 to 4, in, The at least one indication section (7) is checked with respect to the hierarchy by means of topological measurements.

6. The method according to any one of claims 1 to 5, in, The at least one indicator section (7) is checked for delamination by optical inspection.

7. The method according to any one of claims 1 to 6, in, The optical inspection is performed during automated optical inspection.

8. The method according to any one of claims 1 to 7, in, The at least one indicating section (7) is arranged on a technological edge (11) of the circuit board (2).

9. The method according to any one of claims 1 to 8, in, The furnace (8) is a reflow furnace.

10. The method according to any one of claims 1 to 9, in, The circuit board (2) is printed with solder paste (12) before being placed in the furnace (8).

11. The method according to any one of claims 1 to 10, in, Before being placed in the furnace (8), the circuit board (2) is equipped with a top component (13).

12. The method according to any one of claims 1 to 11, in, The first three steps of the method are repeated after a predetermined time in order to determine whether delamination has occurred in the at least one indication section (7) after the predetermined time.

13. The method according to any one of claims 1 to 12, in, The at least one coating (1) is designed such that it absorbs moisture.

14. The method according to any one of claims 1 to 13, in, The at least one coating (1) comprises polyimide.

Images