Flat leadless packaged low-pass filter

Abstract

The utility model relates to a flat leadless packaged low-pass filter, and belongs to the technical field of signal processing and filtering. The filter designed by the utility model is not provided with a lead and a pin, and can be directly welded and mounted on a PCB (Printed Circuit Board) of a product through a bonding pad, so that the lengths of input and output cables of the filter are greatly shortened, the coupling path of interference electromagnetic waves is effectively shortened, and the high-frequency filtering performance of the filter is improved; the internal components are all packaged together, the integration level is high, the size is small, and the weight is light. The device can be installed by using an STM automatic chip mounter, the production efficiency can be improved, and the labor cost can be reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of signal processing and filtering, and in particular relates to a low-pass filter in a flat leadless package. Background Art

[0002] Large electronic equipment or systems often face complex electromagnetic environments, involving various electronic equipment such as radio communications, radar, guidance, navigation, etc., and the radiation frequency range covers the entire electromagnetic spectrum space. In order to ensure the safe and stable operation of various electronic equipment, the GJB151B-2013 standard stipulates the electromagnetic emission and sensitivity requirements of related electronic equipment, among which the tests CE102 ground wire conduction sensitivity and RE102 electric field radiation are directly related to filters.

[0003] At present, lead-type and PCB pin-type filters are mainly used in low-pass filter applications. Since the input and output of lead-type filters are in the form of wires, the wires will be exposed to the complex electromagnetic environment inside the equipment and are easily interfered, resulting in poor overall electromagnetic compatibility of the equipment. The installation position of lead-type filters is also relatively particular and needs to be kept away from high-frequency signals. For engineers who do not have much experience in electromagnetic compatibility, it is difficult to use them; PCB pin-type filters solve the problem of wires to a certain extent, and are directly soldered on the PCB through pins. Due to the shell and internal potting materials, the filter is often not tightly attached to the PCB. Because the filter is large in size, the equipment is at risk of falling off in complex transportation and working environments, and the filter installation process also requires additional glue dispensing.

[0004] Therefore, in order to reduce the radiation path and installation firmness problems, a low-pass filter that meets the following requirements is very necessary:

[0005] 1. There are no input and output wires, which can greatly reduce the packaging structure that is radiated by electromagnetic radiation;

[0006] 2. Small size, easy installation, reliable installation and fixation;

[0007] 3. Meet the requirements of electromagnetic compatibility standards for large electronic equipment or systems (GJB151B-2013, GJB1389A-2005, GJB181A-2003, GJB181B-2012, RTCA / DO-160G), and have good power supply low-pass filtering performance. Utility Model Content

[0008] 1. Technical issues to be resolved

[0009] The technical problem to be solved by the utility model is to provide a low-pass filter without leads and pins and capable of being directly welded and installed on a PCB circuit board of a product.

[0010] (II) Technical solution

[0011] In order to solve the above technical problems, the utility model provides a low-pass filter in a flat leadless package, which has no leads and a flat appearance, and comprises a shell 101, a PCB 102 and a soldering pad 103; the shell 101 is sleeved on the PCB 102; the PCB 102 carries a low-pass filter circuit, and the components in the low-pass filter circuit carried by the PCB 102 include differential mode capacitors, common mode capacitors, differential mode inductors, common mode inductors and resistors; there are multiple soldering pads 103, which are located on the back side of the PCB 102, arranged at intervals, and connected to circuit nodes in the low-pass filter circuit carried by the PCB 102.

[0012] Preferably, the housing 101 is made of plastic, ceramic or metal.

[0013] Preferably, the pad can be soldered to a PCB of a superior product.

[0014] Preferably, the components of the low-pass filter circuit carried by the PCB 102 are installed on the front side of the PCB 102 , that is, inside the housing 101 .

[0015] Preferably, the pads 103 are arranged on two sides or all around.

[0016] Preferably, the low-pass filter is assembled automatically using SMT surface mounting technology.

[0017] Preferably, the low-pass filter controls the passing frequency of the signal through capacitor and inductor elements.

[0018] Preferably, the low-pass filter has certain power supply low-pass filtering performance.

[0019] Preferably, the low-pass filter has a rectangular parallelepiped shape.

[0020] Preferably, the low-pass filter meets the electromagnetic compatibility standard requirements of electronic equipment.

[0021] (III) Beneficial effects

[0022] The utility model designs a low-pass filter with a flat leadless package. The filter itself has no leads and pins and can be directly soldered on the product PCB circuit board through a pad, which greatly shortens the length of the filter input and output cables, effectively shortens the coupling path of the interfering electromagnetic wave, and improves the high-frequency filtering performance of the filter; the internal components are packaged together, with high integration, small size and light weight. The flat leadless package filter of the utility model can be installed using an STM automatic placement machine, which can improve production efficiency and reduce labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a typical type 1 circuit diagram of a low-pass filter;

[0024] Figure 2 This is a typical type 2 circuit diagram of a low-pass filter;

[0025] Figure 3 It is a schematic diagram of the structure of a low-pass filter of a flat leadless package of the utility model;

[0026] Figure 4 The present invention is a schematic diagram of two pins of a low-pass filter package in a flat leadless package. DETAILED DESCRIPTION

[0027] In order to make the purpose, content and advantages of the utility model clearer, the specific implementation methods of the utility model are further described in detail below in conjunction with the drawings and embodiments.

[0028] A typical circuit diagram of a low-pass filter is shown below: Figure 1 , Figure 2 , where L1 is the common mode inductor, L2 is the differential mode inductor, C1 is the differential mode capacitor, C2 is the common mode capacitor, and GND is the structural ground wire. The working principle of the low-pass filter is mainly to control the passing frequency of the signal through the capacitor and inductor components. The low-pass filter allows low-frequency signals to pass through and suppresses high-frequency signals. This means that it can smooth the signal, remove noise and unnecessary details, and retain the main low-frequency components. In the low-pass filter, the capacitor presents high impedance to high-frequency signals and low impedance to low-frequency signals, so the low-frequency signal can pass smoothly. On the contrary, the inductor presents low impedance to high-frequency signals and high impedance to low-frequency signals, thereby hindering the passage of high-frequency signals. Low-pass filters are widely used in signal processing, noise elimination, sound processing and other fields.

[0029] Radio frequency interference can be divided into differential mode interference and common mode interference according to its characteristics. Differential mode interference refers to the interference signal that appears on the two signal lines (usually positive and negative lines) in the circuit, and its peak value is equal to the difference between the signals on the two lines. Differential mode interference generally comes from external electromagnetic radiation, switching interference, ground return interference, etc. These interference signals will be received by different impedances of the circuit, resulting in signal differences at different potentials, which in turn causes differential mode interference. In contrast, common mode interference refers to the interference signal that appears simultaneously on the two signal lines in the circuit, and its peak value is equal to the sum of the signals on the two lines. Common mode interference generally comes from power lines, bus return, common ground interference, etc. These interference signals will enter the circuit in the form of shared paths or shared ground lines, causing interference on the two signal lines at the same time, thereby generating common mode interference. Therefore, four types of devices, common mode inductors, differential mode inductors, differential mode capacitors, and common mode capacitors, are required for filtering.

[0030] A three-dimensional schematic diagram of a low-pass filter in a flat leadless package provided by the utility model is shown in Figure 3 , including a housing 101, a PCB 102, and a pad 103.

[0031] The main function of the housing 101 is to isolate the external environment and protect the internal components. It is generally made of materials such as plastic, ceramic, and metal.

[0032] The main function of PCB102 is to carry Figure 1 , Figure 2 The low-pass filter circuit shown in the figure plays the role of establishing electrical connections and fixing components. The components in the circuit mainly include differential mode capacitors, common mode capacitors, differential mode inductors, common mode inductors, resistors and other components.

[0033] The pads 103 are located on the back of the PCB 102 and are interconnected with certain circuit nodes in the circuit. Through these pads, it can be soldered to the PCB of the upper-level product to establish electrical connection and fixation.

[0034] The PCB 102 is characterized in that only exposed pads are provided on the back of the PCB, and all electronic components are only installed on the front of the PCB 102 , that is, inside the housing 101 .

[0035] The pads 103 are mainly arranged in the following manner: Figure 4 This type of packaging method uses pads designed with intervals. According to the internal structural characteristics of the filter, the pads 103 on the PCB are arranged on both sides or all around, and are welded to the PCB of the upper-level product by welding. The filter designed by this method has no leads and the overall shape is flat, so it is called a low-pass filter with a flat leadless package, which can minimize electromagnetic interference and is firm and reliable after installation.

[0036] It can be seen that the utility model adopts a flat leadless packaging design, and the filter is small in size, light in weight and highly reliable; the leadless filter designed by the utility model greatly shortens the coupling path (wires, pad routing, etc.) that may be affected by electromagnetic interference, thereby improving the filter performance; the filter of the flat leadless package (also known as DFN packaging technology (Dual Flat No-lead Package)) designed by the utility model can use SMT surface mounting technology (SurfaceMount Technology) to achieve automated assembly and welding, which can greatly improve production efficiency; compared with the lead filter with the same parameters, the flat leadless package filter realized by the utility model is theoretically less susceptible to radiation interference and has improved performance.

[0037] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A low-pass filter in a flat leadless package, characterized in that: The low-pass filter has no leads and a flat appearance, and comprises a housing (101), a PCB (102) and a solder pad (103); the housing (101) is sleeved on the PCB (102); the PCB (102) carries a low-pass filter circuit, and the components in the low-pass filter circuit carried by the PCB (102) include differential mode capacitors, common mode capacitors, differential mode inductors, common mode inductors and resistors; and there are a plurality of solder pads (103), which are located on the back of the PCB (102), arranged at intervals, and connected to circuit nodes in the low-pass filter circuit carried by the PCB (102).

2. The low-pass filter according to claim 1, wherein The housing (101) is made of plastic, ceramic or metal.

3. The low-pass filter according to claim 1, wherein The pads can be soldered to a PCB of a parent product.

4. The low-pass filter according to claim 1, wherein The components of the low-pass filter circuit carried by the PCB (102) are installed on the front side of the PCB (102), that is, inside the housing (101).

5. The low-pass filter according to claim 1, wherein The pads (103) are arranged on two sides or all around.

6. The low-pass filter according to claim 1, wherein The low-pass filter is assembled automatically using SMT surface mounting technology.

7. The low-pass filter according to claim 1, wherein The low-pass filter controls the passing frequency of the signal through capacitor and inductor components.

8. The low-pass filter according to claim 1, wherein The low-pass filter has certain power supply low-pass filtering performance.

9. The low-pass filter according to claim 1, wherein: The low-pass filter has a rectangular parallelepiped shape.

10. The low-pass filter according to any one of claims 1 to 9, characterized in that The low-pass filter meets the electromagnetic compatibility standard requirements of electronic equipment.

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