High-frequency amplifier arrangement

Abstract

1. High-frequency amplifier arrangement (1) suitable for generating output powers ≥ 1kW at frequencies ≥ 2MHz for plasma excitation, comprising: a. a multi-layered conductor board (2), b. two transistors (S1, S2) which are each connected at their first power terminal to a common connection point, in particular a ground connection point (5), wherein the transistors (S1, S2) are of the same design and are arranged on the multilayer circuit board (2), c. a power transformer (7) whose primary winding (6) is connected to the second power terminal of the transistors (S1, S2), wherein the primary winding (6) and the secondary winding (4) of the power transformer (7) are each designed as planar conductor tracks arranged in different layers (61, 62) of the multilayer printed circuit board (2), d. a heat distributor (50), e. a thermally conductive leveling layer (52) which is firmly connected with its first surface to the first surface of the circuit board (2), and f. a connecting layer (53) which is firmly connected with its first surface to the second surface of the heat-conducting leveling layer (52) and with its second surface is firmly connected to the heat distributor (50).

Description

[0001] The invention relates to a High-frequency amplifier arrangement which is suitable for generating output powers ≥ 1 kW at frequencies ≥ 2 MHz for plasma excitation, comprising two transistors, each having a first and a second power connection and a control connection, wherein both transistors (S1, S2) are connected by their first power connection, in particular source connection, each to a common connection point, in particular ground connection point, wherein the transistors are of identical design and are arranged on a multi-layer printed circuit board, and a power transformer, the primary winding of which is connected to the respective second power connections, in particular drain connections, of the transistors, wherein the primary winding and the secondary winding of the power transformer are each designed as planar conductor tracks which are arranged in different layers of the multi-layer printed circuit board.

[0002] It is known to use transistors, particularly bipolar transistors or LDMOS transistors, to generate power suitable for plasma excitation. For plasma excitation, it is particularly desirable to be able to operate the high-frequency amplifier arrangement in Class F amplifier mode or in Class F inverse mode. This can result in considerable heat generation, especially when power is reflected from a load and must be converted into heat in the high-frequency amplifier arrangement.

[0003] EP3317966B1 discloses that the printed circuit board can be arranged on a metallic cooling plate for cooling. For this purpose, the printed circuit board of EP3317966B1 has a bottom layer, wherein the bottom layer is formed as a metallic layer that serves as a reference ground. However, the heat transfer from the printed circuit board to the cooling plate is not optimal. The board often does not lie flat on the cooling plate. To counteract the lack of heat transfer caused by this disadvantage, thermal paste is used. However, this is disadvantageous in the manufacturing process and can age, which can further deteriorate the heat transfer. The object of the present invention is to provide a high-frequency amplifier arrangement which ensures improved heat dissipation.

[0004] This object is achieved according to the invention by a high-frequency amplifier arrangement which is suitable for generating output powers ≥ 1 kW at frequencies ≥ 2 MHz for plasma excitation, comprising: a. two transistors, each having a first and a second power terminal and a control terminal, wherein both transistors are connected by their first power terminal, in particular source terminal, to a common connection point, in particular ground connection point, wherein the transistors are of similar design and are arranged on a multilayer printed circuit board, b. a power transformer, the primary winding of which is connected to the respective second power terminals, in particular drain terminals, of the transistors, wherein the primary winding and the secondary winding of the power transformer are each designed as planar conductor tracks arranged in different layers of the multilayer printed circuit board, c. a heat distributor, d. a thermally conductive leveling layer, which is firmly connected with its first surface to the first surface of the circuit board, e. a connecting layer which is firmly connected with its first surface to the second surface of the heat-conducting compensating layer and which is firmly connected with its second surface on the side facing away from the compensating layer to the heat spreader.

[0005] By “similar design” we mean that the transistors are of the same type, e.g. both VMOS, LDMOS, IGBT transistors, have the same design, e.g. P-channel, n-channel etc. and have the same size, the same connections and electrical properties.

[0006] By firmly connected we mean that the connection is firm and permanent, such as gluing, welding, soldering or pressing and preferably only removable with high heat and / or mechanical pressure.

[0007] In particular, the connection can be designed to be form-fitting. This prevents air pockets and ensures good heat conduction.

[0008] The thermally conductive leveling layer is designed to conduct heat from the circuit board toward the heat spreader. It can compensate for unevenness caused by traces, windings, or contact pads on the underside of the circuit board, for example, and provide a uniform and flat surface toward the heat spreader.

[0009] The thermally conductive leveling layer can consist of a prepreg or unreinforced adhesive.

[0010] The bonding layer may comprise a resin-based adhesive. It may be thinner than the thermally conductive compensating layer. The connecting layer may comprise an adhesive film.

[0011] Together, the two layers can form a solid connection with good heat conduction to the heat spreader.

[0012] The circuit board and the heat spreader may have different coefficients of expansion. This can lead to mechanical stresses due to temperature changes, particularly in larger surfaces, e.g., with a length greater than 10 cm. Temperature changes are almost unavoidable during operation. This is especially the case with significant load changes and changes in the load's impedance, resulting in significant reverse power, as is frequently the case with high-frequency amplifier arrangements, and particularly in plasma processes. Such stresses can lead to detachment of the fixed connections, which is often only discovered once damage to the high-frequency amplifier arrangement has already occurred due to overheating. To counteract such disadvantages, the circuit board can have at least one expansion gap.This or these can divide the circuit board into several sub-areas with dimensions of less than 20 cm in length, in particular less than 10 cm in length.

[0013] Alternatively or additionally, the heat-conducting compensation layer may have an expansion gap. The expansion gap of the thermally conductive compensation layer can, in particular, coincide with the expansion gap of the circuit board in the top view.

[0014] In one aspect, the high-frequency amplifier arrangement can have a cooling plate with a cooling channel for conducting a cooling liquid. This allows heat to be dissipated particularly effectively.

[0015] The cooling plate can be connected to the heat distributor, in particular be firmly connected.

[0016] The heat spreader can be constructed of an insulating material. In particular, it can be made of a ceramic material. This material offers excellent electrical insulation properties, very low dielectric losses, making it particularly suitable for RF amplifiers, and excellent thermal conductivity and heat dissipation properties.

[0017] In one aspect, the high-frequency amplifier arrangement can have a driver circuit for controlling the transistors, which is also arranged on the circuit board. This allows for particularly good cooling of this driver circuit. Such a driver circuit can comprise an integrated circuit that combines several electronic units in one housing.

[0018] The transistors used are preferably two bipolar transistors or two LDMOS transistors. These are particularly suitable for push-pull operation.

[0019] The planar conductor tracks of the primary and secondary windings are preferably embedded in the circuit board material and located in different planes, i.e., they are spaced apart from one another, with circuit board material arranged between the conductor tracks. Such an arrangement enables good heat dissipation. Furthermore, such an arrangement makes it possible for the fundamental wave, i.e., the high-frequency signal generated by the high-frequency amplifier arrangement at a predetermined fundamental frequency (which is the operating frequency of the high-frequency amplifier arrangement), and odd harmonics to be excited exclusively in differential mode, and even harmonics exclusively in common mode, in ideal push-pull operation for differential-mode signals.By choosing the turns ratio of the primary winding to the secondary winding, an impedance can be provided for each of the two transistors at the fundamental frequency depending on the desired behavior of the amplifier arrangement. The even and odd harmonic frequency components that can arise when the high-frequency amplifier arrangement is excited due to non-linearities in the transistors can be terminated with a more highly reflective termination with respect to the impedance of the fundamental wave in order to dissipate less energy at these frequencies and increase efficiency. A more highly reflective termination for a harmonic frequency is one that has a higher reflection factor than that for the fundamental wave. A more highly reflective termination can, for example, be a short circuit or an open circuit for the corresponding harmonic frequency. This can be achieved using additional filters tuned to the corresponding harmonic frequency.

[0020] The phase of the reflection factors can be selected so that the current and voltage waveforms at the transistors are shaped to minimize overlap. This results in reduced power dissipation at the transistors.

[0021] The primary and secondary windings can be vertically coupled. The coupling can be influenced by the distance and the material between them.

[0022] The primary winding can be arranged below the secondary winding.

[0023] The transistors can be arranged in a common housing. In particular, the transistors can be arranged in a single assembly (package). This results in a compact design and reduced manufacturing costs.

[0024] The vertical distance between the primary winding and the secondary winding can be less than half the width of a conductor path forming the primary or secondary winding. This allows a compromise to be achieved between increased magnetic coupling (small distance) and reduced capacitive coupling (large distance).

[0025] A metallic layer can be formed between the heat spreader and the circuit board, which can serve, in particular, as a reference ground. This metallic layer can also be used to ensure good heat transfer to the heat spreader. Such a metallic layer can be arranged between the thermally conductive compensating layer and the connecting layer.

[0026] Additionally or alternatively, such a metallic layer can be arranged between the connecting layer and the heat spreader.

[0027] The circuit board can be arranged on a metallic cooling plate via the thermally conductive leveling layer and the connecting layer and the heat spreader.

[0028] The vertical distance between the primary and secondary windings of the power transformer and the heat spreader can be greater than the distance between the primary and secondary windings. This ensures that the capacitance per unit length from the layers containing the windings to ground and the capacitive coupling between the layers containing the windings is small enough for the desired matching behavior, i.e., ideal transformation. On the other hand, the thermal resistance to the cooling plate is small enough to dissipate losses in the primary and secondary windings toward the cooling plate.

[0029] The horizontal extension of the primary winding and the secondary winding in the horizontal longitudinal direction and in the horizontal transverse direction of the circuit board can each be < λ / 30, where λ is the wavelength of the high-frequency signal generated by the high-frequency amplifier arrangement.

[0030] A capacitance, in particular a capacitor, can be connected in parallel to the primary winding and the secondary winding of the power transformer. This capacitance, for example in the form of a lumped capacitor, together with the respective self-inductance of the primary winding or the secondary winding, can represent a high impedance at the fundamental frequency, particularly close to parallel resonance. On the primary side of the power transformer, this capacitance can be formed in part from the output capacitance of the transistor. The parallel capacitance on the primary side can also be composed of a combination of differential-mode capacitance between the two drains or collectors of the transistor pair and the common-mode capacitances from the two drains or collectors towards ground.

[0031] The primary winding can be designed symmetrically so that the primary side presents the same load for both transistors. This creates a high-impedance termination compared to the fundamental impedance, so that the second harmonic is subjected to a high-impedance load during common-mode excitation.

[0032] The number of turns for the primary and secondary windings of the power transformer can be selected to achieve a desired impedance transformation. In particular, the turns ratio can be 1:2; preferably, the primary winding can have one turn and the secondary winding two turns.

[0033] The primary winding of the power transformer can have a center tap to supply DC to the transistors.

[0034] A shielding plate can be arranged on the circuit board. This can also be used to direct a cooling airflow.

[0035] A network with an inductor and / or a capacitor can be connected to the center tap. This allows even-numbered harmonics to be terminated. A series circuit consisting of this network and half the primary winding at the center tap should be designed with high impedance for twice the fundamental frequency.

[0036] The drains and collectors of the transistors can be connected by a series circuit comprising an inductor and a capacitor. The capacitor can be a concentrated or distributed capacitor. The series circuit of inductor and capacitor can be dimensioned such that a low-impedance termination is achieved at the third harmonic. Quantitatively, this allows for a low-impedance termination compared to the fundamental impedance.

[0037] The inductance of the series circuit can be formed as a planar inductance on one layer of the circuit board.

[0038] To control the transistors, a signal transformer can be provided, the secondary winding of which is connected at a first end to the gate or base terminal of one transistor and at a second end to the gate or base terminal of the other transistor.

[0039] Harmonics higher than the fourth have only a minor impact on the performance of the high-frequency amplifier array. Optionally, they can be connected directly to the drains or collectors via a low-impedance capacitor. This prevents the excitation of parasitic resonances caused by very high harmonics and significantly improves stability.

[0040] A high-frequency excitation arrangement according to the invention is suitable for generating an approximately half-sinusoidal voltage waveform and an approximately rectangular current waveform. This corresponds to Class F inverse operation or, depending on the choice of fundamental impedance and the corresponding harmonics, a case from the Class F inverse continuum.

[0041] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, based on the figures of the drawing, which illustrate details essential to the invention, and from the claims. The features shown therein are not necessarily to scale and are presented in such a way that the special features of the invention can be clearly seen. The various features can be implemented individually or in combinations in variants of the invention.

[0042] Furthermore, the insulating circuit board and the heat spreader can be joined by heating and pressing together a prepreg sandwiched between them. "Prepreg" is a common material name, shortened from "preimpregnated." This term typically refers to pre-impregnated, usually flat, sheet-like textile semi-finished products with a thermoplastic or thermosetting matrix, such as unidirectional layers of threads, fabrics, or scrims, often with perpendicularly arranged threads. Prepregs are cured under temperature and pressure to manufacture components. They are prefabricated, for example, in sheet form, wound on rolls. The term prepreg encompasses not only unidirectionally reinforced or sheet-like semi-finished products, but also other preforms of essentially any shape, which, in the broadest sense, consist of a fiber-filled, uncured thermosetting matrix.The matrix is ​​in a partially cross-linked state and is pasty to solid, but can be liquefied again by heating.

[0043] Prepregs are machine-processable and are therefore frequently used in automated processes. They produce consistent, high-quality products. Advantages include their low undulation and high fiber volume fraction. Curing at high temperatures enables short cycle times in further processing. Processing requires significant investment, e.g., for autoclaves, placement robots, and refrigerated storage. Such prepregs are generally used to join several circuit boards together to form a multilayer PCB. To ensure a secure and long-lasting joint, the materials to be joined should have very similar properties regarding their expansion under heating. However, this is not necessarily the case for the circuit board and the heat spreader, especially if the heat spreader is made of ceramic. This initially spoke against such a connection.However, ceramic exhibits very good thermal conductivity and, at the same time, very good electrical insulating properties, as well as low dielectric losses when isolating high-frequency signals at high voltages. Contrary to expectations, however, tests have shown that, even with small dimensions, a secure and long-lasting bonding of materials with different properties, such as ceramic with FR-4 and / or ceramic with PTFE material, is possible. "Small dimensions" here means a bonding area of ​​less than 400 cm. 2 and / or with a maximum length of 20 cm.

[0044] The entire high-frequency amplifier arrangement can be mounted on a heat sink via the heat spreader, which dissipates the heat, e.g., from the planar inductors. Such a heat sink can preferably be metallic, in particular made of aluminum and / or copper. The heat sink can also be a fluid heat sink, which has at least one cooling channel through which a fluid flows, through which the heat is dissipated. A thermal paste can be applied between the heat sink and the heat spreader, and the impedance matching component can be attached to the heat sink via brackets.

[0045] Furthermore, the high-frequency amplifier arrangement can have an impedance matching on the circuit board, which can also be at least partially planar, in particular can have planar inductors.

[0046] The high-frequency amplifier arrangement can be used in a plasma process supply system or a plasma process system. Such a plasma process supply system can have an additional impedance matching circuit in addition to the high-frequency amplifier arrangement.

[0047] Such an impedance matching circuit may also comprise a comparable printed circuit board cooling arrangement, as described, for example, in patent application DE 102023104960.7, filed on February 28, 2023.

[0048] The external impedance matching circuit can be connected, on the one hand, to an RF power supply having a described high-frequency amplifier arrangement, and, on the other hand, can be designed to be connected to a plasma processing arrangement. In a plasma processing system, such a plasma processing arrangement can be present and connected to the impedance matching circuit.

[0049] The plasma processing arrangement can be supplied with electrical power provided by the RF power supply via the impedance matching circuit.

[0050] The schematic drawing shows embodiments of the invention in various stages of use and is explained in more detail in the following description.

[0051] Show it. Fig. 1 is a circuit diagram of a high-frequency amplifier arrangement according to the invention; Fig. 2 a perspective view of a planar power transformer; Fig. 3 a sectional view through a circuit board of a high-frequency amplifier arrangement; Fig. 4 Current and voltage waveforms that occur at the transistors of the high-frequency amplifier arrangement.

[0052] The Fig. 1 shows a first embodiment of a high-frequency amplifier arrangement 1. The high-frequency amplifier arrangement 1 comprises a printed circuit board 2 on which a module 3 is arranged. The printed circuit board 2 can be a multilayer printed circuit board. The module 3 has two transistors S1, S2 designed as LDMOS transistors, which are of identical design and whose source terminals are each connected to a ground connection point 5. The module 3 can be arranged on a substrate. The module 3 can be arranged in a housing. The housing of the module 3 can be arranged in a through-hole in the printed circuit board 2. The terminals of the module 3 can be contacted on the printed circuit board 2.

[0053] The drain terminals of transistors S1 and S2 are each connected to one end of a primary winding 6 of a power transformer 7, which is part of an output network. The secondary winding 4 of the power transformer 7 is connected to ground 8 and to a high-frequency output 9.

[0054] The source terminals of transistors S1 and S2 are each connected to ground via a capacitor 32 and 33, respectively. This connection is made via a through-hole in the heat spreader of transistors S1 and S2.

[0055] The high-frequency amplifier arrangement 1 further comprises a signal transformer 10 having a primary winding 11 connected, for example, via a matching network 18 to a high-frequency input 12. The secondary winding 13 of the signal transformer 10 is connected, on the one hand, to the gate terminal 15 of the transistor S1 via a resistive element 14, in particular a resistor. On the other hand, the secondary winding 13 is connected to the gate terminal 17 of the transistor S2 via a resistive element 16, in particular a resistor. The resistive elements 14, 16 and the secondary winding 13 are thus connected in series. The signal transformer 10 is also arranged on the circuit board 2, just like the power transformer 7.

[0056] The printed circuit board 2 rests flat on a cooling plate 25, which can also be connected to ground 26. The assembly 3 can be mounted on a copper plate for cooling. The copper plate can serve to transfer heat from the assembly 3 to the cooling plate 25, and in particular to spread the heat. The copper plate can be arranged in the same through-hole in the printed circuit board 2 as the assembly 3. The copper plate can have a larger surface area than the surface of the assembly 3 facing the cooling plate 25. The through-hole can be stepped, adapted to the surfaces of the copper plate and the assembly 3.

[0057] The Fig. Figure 1 further shows that a capacitor 35 is provided in parallel with the primary winding 6 of the power transformer 7. A capacitor 36 is also provided in parallel with the secondary winding 4 of the power transformer 7.

[0058] The primary winding 6 of the power transformer 7 has a center tap 37, which serves to supply DC to the transistors S1, S2. A network 38, which may include an inductor and / or a capacitor, is connected to the center tap 37. In particular, a series circuit comprising a capacitor and an inductor may be provided. Alternatively, a capacitance to ground and a series inductor could be provided.

[0059] The drains and collectors of transistors S1, S2 are connected by a series circuit 40 comprising an inductor 41 and a capacitor 42. This series circuit 40 serves as a low-impedance termination of the third harmonic.

[0060] Optionally, a matching network 43 can also be provided, which has two capacitors 44, 45 whose junction point is connected to ground. This allows the primary winding 6 of the power transformer 7 to be tuned.

[0061] Fig. Figure 2 shows the power transformer 7. The primary winding 6 is arranged below the secondary winding 4. The primary winding 6 has one turn, while the secondary winding 4 has two turns. The primary winding 6 and the secondary winding 4 occupy approximately the same area. The extension in the x-direction and in the y-direction, i.e. in the longitudinal and transverse directions of the circuit board 2, is in each case less than λ / 30, where λ is the wavelength of the high-frequency signal to be generated. It can also be seen that the primary winding 6 has a center tap 37 (the center tap 37 is not connected to the secondary winding 4, which is evident from the Fig. 2 may not be so clear).

[0062] Both the primary winding 6 and the secondary winding 4 are arranged in different layers 61, 62 of the circuit board. Fig. 2, one can also see that the primary winding 6 and the secondary winding 4 are each formed from conductor tracks. Fig. 2 also shows the planar inductance 41, which is also arranged in a layer 63 of the circuit board 2, located under the layers 61, 62.

[0063] The Fig. 3 shows a sectional view through a printed circuit board 2. On the top side of the printed circuit board 2, connection pads 60 are provided for connecting discrete components. Corresponding connection pads could also be provided on layer 62. The heat spreader 50 is flat. It is connected over a large area to a cooling plate 25. The cooling plate 25 has a plurality of cooling channels 54 for conducting coolant. These can have different cross-sections, e.g., round, oval, semicircular, rectangular, or polygonal, as shown here. The primary winding 6 and the secondary winding 4 are arranged in layers 61, 62 of the printed circuit board. The distance b between the primary winding 6 and the secondary winding 4 is preferably less than half the width c of a conductor track of the primary winding 6 or the secondary winding 4.The distance d from the primary winding 6 to the heat spreader 50 and also the distance e from the secondary winding 4 to the heat spreader 50 are each greater than the distance b. Connecting lines and also the planar inductor 41 can be provided in layer 63.

[0064] In Fig. 3 further shows the thermally conductive compensating layer 52, which is firmly connected by its first surface to the first surface of the circuit board 2. Also shown is the connecting layer 53, which is firmly connected by its first surface to the second surface of the thermally conductive compensating layer 52 and by its second surface, which is located on the side facing away from the compensating layer 52, is firmly connected to the heat spreader 50.

[0065] In Fig. 3 also shows that the circuit board 2 has at least one expansion gap 55. In this embodiment, this expansion gap 55 also extends over the thermally conductive compensating layer 52, so that the latter also has an expansion gap 55, which here is preferably congruent with the expansion gap 55 in the circuit board 2 in plan view.

[0066] A shielding plate 56 is arranged on the circuit board 2. This can also be used to direct a cooling airflow.

[0067] The Fig.Figure 4 shows a voltage waveform 100 that is almost half-sinusoidal and a current waveform 101 that is essentially rectangular. The voltage and current waveforms 100 and 101 are established at transistors S1 and S2 when the high-frequency amplifier arrangement 1 is correctly tuned. It can be seen that the voltage waveform 100 and the current waveform 101 overlap only slightly, which results in only a small amount of heat being generated in the transistors S1 and S2. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] EP 3317966B1

[0003] FROM 102023104960.7

[0047]

Claims

[1] High-frequency amplifier arrangement (1) suitable for generating output powers ≥ 1 kW at frequencies ≥ 2 MHz for plasma excitation, comprising: a multilayer circuit board (2), b. two transistors (S1, S2), each having a first and a second power terminal and a control terminal, wherein both transistors (S1, S2) are each connected by their first power terminal, in particular source terminal, to a common connection point, in particular ground connection point (5), wherein the transistors (S1, S2) are of similar design and are arranged on the multilayer printed circuit board (2), c. a power transformer (7), the primary winding (6) of which is connected to the respective second power terminal, in particular the drain terminal, of the transistors (S1, S2), wherein the primary winding (6) and the secondary winding (4) of the power transformer (7) are each designed as planar conductor tracks which are arranged in different layers (61, 62) of the multilayer printed circuit board (2), d. a heat distributor (50), characterized by that the high-frequency amplifier arrangement (1) further comprises: e. a heat-conducting compensating layer (52) which is firmly connected with its first surface to the first surface of the circuit board, f. a connecting layer (53) which is firmly connected with its first surface to the second surface of the heat-conducting compensating layer (52) and is firmly connected with its second surface, which lies on the side facing away from the compensating layer (52), to the heat distributor (50). [2] High-frequency amplifier arrangement (1) according to claim 1, characterized by that the heat-conducting compensating layer (52) consists of a prepreg or unreinforced adhesive. [3] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized by that the connecting layer (53) comprises a resin-based adhesive. [4] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized by that the connecting layer (53) comprises adhesive films. [5] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized by that the circuit board (2) has at least one expansion gap (55). [6] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized by that the heat-conducting compensating layer (52) has an expansion gap (55). [7] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized bythat the high-frequency amplifier arrangement (1) has a cooling plate (25) with a cooling channel (54) for the passage of a cooling liquid. [8] High-frequency amplifier arrangement (1) according to claim 7, characterized by that the cooling plate (25) is connected to the heat distributor (50), in particular flatly. [9] High-frequency amplifier arrangement (1) according to one of the preceding claims, characterized by that the high-frequency amplifier arrangement (1) has a driver circuit for controlling the transistors, which is in particular also arranged on the printed circuit board (2).

Images