1. According to the heating method, the soldering iron can be divided into two types: internal heat type and external heat type.
The characteristics of the internal heating type soldering iron: the advantage is high thermal efficiency (up to 85%-90%), the tip of the soldering iron is fast, the temperature is high, the volume is small, and the weight is light at the same power; the disadvantage is that the inner heating type iron core is concentrated during use. It is easy to cause the tip to be oxidized and burned, and it is easy to be damaged for a long time, so its life is short, and it is not suitable for a high-power soldering iron. Features of external thermal soldering iron: The advantages are durable, long service life, stable temperature during long working hours, and it is not easy to burn components during soldering. The disadvantage is that it is bulky and has low thermal efficiency.
2. Commonly used resistors have nominal values ​​of E48, E24, E12, and E6.
3. Commonly used marking methods for resistance are: straight label method, text symbol method, digital representation method and color label method.
4. Commonly used manual welding tools are: electric iron, electric air gun and iron frame, etc. Commonly used automatic welding equipment includes: wave soldering machine and reflow soldering machine equipment.
14. Common anti-interference measures are: shielding, decoupling, frequency selection, filtering, and grounding.
16. The process of assembly of electronic products is assembly preparation, assembly, commissioning, inspection, packaging, storage or delivery.
17. The safety inspection of electronic products is the two main aspects of insulation resistance and insulation strength.
18. The production of electronic products refers to the whole process of product development, development and launch.
19. The design documents generally include various drawings (such as circuit schematics, assembly drawings, wiring diagrams, etc.), function description drawings, and component lists.
20. The classification of design documents is: a. Divided into drawings, sketches, texts and tables according to the content of the expression. b. According to the formation process, it is divided into trial production documents and production documents. c. According to the drawing process and the use characteristics are divided into sketches, original drawings, base maps, and media containing programs.
21. The content of electronic product debugging includes the stage before power-on inspection, power-on debugging and machine debugging.
22. The general steps for debugging fault finding and processing are observation, test analysis and judgment of faults, troubleshooting, function and performance checks.
23. Common methods for commonly used debugging fault finding and processing are: observation method, measurement method, signal method, comparison method, replacement method, heating and cooling method.
24. From the microscopic point of view, the soldering process can be divided into three stages: the wet phase, the diffusion phase, and the solder joint formation phase.
25. Wave soldering features: high production efficiency, most suitable for large-scale welding of single-sided printed circuit boards, and soldering temperature, time, solder and solder usage, etc., can be more perfect control in wave soldering. However, wave soldering is likely to cause grounding of the solder joint bridge and requires repair repair.
26. Briefly describe the detection method of resistors, capacitors, inductors, diodes, switching devices, and speakers with a multimeter.
Resistance: Measure with the ohmmeter of the multimeter. Capacitance: The highest resistance file of the analog multimeter; Inductance: Usually measured by a 1 ohm 10 ohm multimeter; if the measured coil resistance is much larger than the nominal value or infinity, infinity. The measured resistance is less than the nominal value, and the coil is internally short-circuited; the diode: the multimeter measures the forward resistance of the diode to be small, and the reverse resistance is large. If the positive direction resistance differs by several hundred times or more, this indicates that the one-way conductivity is good. Generally choose 100 Euro or 1000 Euro; Switching device: The ohmic gear of the multimeter measures the insulation resistance and contact resistance of the switching coil. The mechanical switch insulation resistance is less than several hundred kilo ohms, leakage, contact switch is greater than 0.5 ohm, poor contact. The electromagnetic switch coil resistance is in the tens of ohms and several thousand ohms. The insulation resistance and contact resistance are the same as those of the mechanical switch. Electronic switch, detecting diode unidirectional conductivity and triode good or bad; speaker; multimeter 1 European gear measuring DC resistance, if less than nominal, normal, greater than internal disconnection. Good speaker test sounds, no sound, the voice coil is stuck.
Part drawing: First understand the name, material, scale, actual size, nominal tolerance and use of the part from the title bar, then understand the general shape of the part from the given view, and then use according to the given views. The shape analysis method and the line surface analysis method read out the shape and structure of the parts.
Block diagram: read from left to right, top-down or according to the direction of the signal flow, understand the name, symbol, function and relationship of each part while reading, so as to master the electronic The overall composition and function of the product.
Electrical schematic: first understand the role, characteristics, uses and related technical indicators of electronic products, combined with the electrical principle block diagram from top to bottom, from left to right, from the signal input end according to the signal flow, a unit of a unit circuit familiar, has been To the output of the signal, to understand the ins and outs of the circuit, to master the connection between the components and the circuit, to analyze the working principle of the electronic product.
Assembly drawing: First look at the title bar to understand the name and figure number of the figure; then look at the detail column to understand the serial number, name, material, performance and use of each part in the drawing, and find each part in the assembly according to the serial number. Position; then carefully analyze the mutual positional relationship and assembly connection relationship of each component on the assembly drawing; finally, on the basis of seeing and understanding the assembly drawing, according to the requirements of the process documentation, the assembly is assembled according to the assembly drawing.
Wiring diagram: first look at the title bar, the schedule, then refer to the electrical schematic, understand the wiring diagram, and finally connect the wire to the specified position according to the requirements of the process documentation.
Printed circuit board assembly drawing: It should be completed together with the electrical schematic diagram. (1) Read the corresponding electrical schematic diagram to find out the key components of the basic constituent circuit in the electrical schematic diagram. (2) Find the ground terminal on the printed circuit board. (3) According to the reading direction of the printed board, combined with the positional relationship of the key components of the circuit in the circuit and the relationship with the grounding terminal, the reading of the printed circuit board assembly drawing is gradually completed.
31. The technical requirements for component lead forming are:
1) After the lead is formed, the component body should not be cracked, the surface package should not be damaged, and the bent portion of the lead is not allowed to be stamped, indented and cracked.
2) After the lead is formed, the diameter reduction or deformation should not exceed 10%, and the surface plating peeling length should not exceed 1/10 of the lead diameter.
3) After the lead is formed, the marking of the component (including its model, parameters, specifications, etc.) should be upward (horizontal) or outward (vertical), and note that the reading direction of the marking should be consistent to facilitate inspection and future service.
4) If there is a fusion point on the lead, no excavation point is allowed between the fusion point and the component, and the distance between the fusion point and the bending electric power is kept at 2 mm.
32. What are the precautions for the detection, maintenance and use of the soldering iron?
(1) Detection of soldering iron: The detection of the quality of the soldering iron can be carried out by a combination of visual inspection and ohmic detection using a multimeter. The visual inspection is mainly to check whether the power cord is loose and the core of the soup is broken, whether the soldering iron is oxidized or loose, and whether the fixing screw is loose.
(2) Maintenance of electric soldering iron: Before the first use of ordinary new soldering iron, use the trowel to remove the oxide layer on the surface of the soldering iron tip, and immediately apply tin to the soldering iron tip to enhance the soldering performance and prevent oxidation.
(3) Precautions for use;
1. Before use, carefully check the power plug and power cord for damage, and whether the shoulder iron is loose.
2. During the soldering process, the soldering iron should not be everywhere. If it is not soldered, it should be placed on the soldering iron frame to avoid scalding other items. Note that the power cord should not be placed on the soldering iron tip, and one side will burn the insulation layer and cause an accident.
3. When the soldering iron is in use, it cannot be struck or shaken with force. The tapping is easy to deform and damage the tip, and the solder that flies out is easy to crise people. If there is too much solder on the tip, it can be wiped off with a cloth.
4. When the soldering iron is not used for a long time, turn off the power of the soldering iron. Long time at high temperature will accelerate the oxidation of the soldering iron tip, affecting the soldering performance, the resistance wire of the iron core is also easy to burn out, reducing the service life of the soldering iron.
5. Turn off the power and disconnect the power plug after use. After cooling, clean the tip and retract the soldering iron from the kit.
37. Briefly describe the advantages and disadvantages of lead-free soldering technology.
38. What are the basis and conditions for component selection in the production process of electronic products?
Selection basis: The specifications and models of the components indicated on the electrical schematic diagram of the components. The parameters are selected. When the marking parameters of some components are not complete, or the conditions used are inconsistent with the technical data, but when selecting and adjusting some parameters of the components, but try to be close to the original design requirements, maintain the performance indicators of the electronic products.
in principle;
1. Under the premise of satisfying product functions and technical indicators, the number and variety of components should be minimized. It is simple to facilitate the installation of the circuit.
2. In order to ensure the quality of the products, the selected components must be filtered after high temperature storage and power aging, and the qualified products can be used.
3. From the perspective of cost reduction and economic rationality, the selected components do not need to be selected too precisely under the conditions of meeting the technical requirements of the circuit, and may have a certain tolerance.
39. What are the technical requirements for component mounting during the assembly of printed boards?
1. The direction of the components should be in accordance with the requirements specified in the drawings. After installation, the signs on the components can be seen.
2. The polarity of the component must not be installed incorrectly. The corresponding casing should be placed before installation.
3, the installation height should meet the requirements of the requirements, the components of the uniform specifications should be installed at the same height.
4, the installation order is generally low and then high, first light and then heavy, first easy and then difficult, first general components and special components,
5. The distribution of components on the printed board should be as uniform as possible, and the arrangement should be neat and tidy.
6. The lead diameter of the component and the aperture of the printing plate should have a qualified gap of 0.2~0.4mm.
7, special components have their special treatment methods.
40. Briefly describe the production process and inspection methods of the printed version. (incomplete)
Production process: base film processing, graphics transfer, etched, mechanical processing and quality inspection of printed circuit boards.
Inspection method: visual inspection, connectivity test, insulation resistance test, weldability test
41. Design requirements for the structural form of electronic products.
Design requirements,
1. Realize various functional indicators of the product, work reliably and have stable performance.
2, small size, beautiful appearance, easy to operate, cost-effective
3, good insulation performance, high insulation strength, in line with national safety standards.
4. It is convenient to assemble, debug and maintain.
5, the product consistency is good, suitable for mass production or automated production.
42. What is the final assembly of electronic products, and what is the order and requirements of the final assembly?
The final assembly of electronic products is to form the parts of the whole machine, the inserts and the middle of the unit functions (such as electromechanical components, printed circuit boards, bases and panels, etc.), according to the design requirements, assembly, connection, and composition The function of the complete electronic whole product process, while the whole machine is adjusted and tested.
Order: first light and then heavy, first small and then large, first riveted and then loaded, first installed and then welded, first inside and outside, first flat and then high, the previous process must not affect the next process.
Claim;
1. The relevant parts or components that constitute the whole machine before final assembly must be debugged and inspected. Unqualified parts or components are not allowed to be put into the assembly line. The qualified parts must be kept clean.
2, the assembly process should be based on the structure of the machine, the application of a reasonable installation process, with economic, college, advanced assembly technology, is the product to achieve the desired results, to meet the product requirements in terms of functions, technical indicators, economic indicators.
3, strictly abide by the order of the final assembly, pay attention to the connection between the front and the back.
4. During the assembly process, the components and components are not damaged, and the surface coating of the casing, components and components is avoided. It does not damage the insulation of the whole machine, guarantees the orientation, position and polarity of the mounting parts, ensures the electrical performance of the product is stable, and has sufficient mechanical strength and stability.
5. The products that are mass-produced by small machines are always installed at the station arranged on the assembly line.
43. The assembly of electronic products can be divided into several assembly levels.
1. Component-level assembly (first-stage assembly): Refers to the assembly of circuit components and integrated circuits, which is the lowest level in assembly. Its characteristic is that the structure is inseparable.
2. Plug-in assembly (second-level assembly): refers to the assembly and interconnection of printed circuit boards or boards with components.
3. System-level assembly (3rd quarter assembly): It is a plug-in assembly that is assembled into a functional electronic device through connectors, wires and cables.
44. The quality inspection of electronic product assembly must mainly include visual inspection, correctness inspection of the assembly, safety inspection, and test the contents of the inspection.
1. Appearance inspection: no damage on the surface, no scratches on the coating, shedding, no cracking of the metal structure, de-soldering, no damage to the wires, firm installation of the components, and compliance with the provisions of the electronic product design documents, the active part of the machine Free movement, no extras in the machine.
2. Check the correctness of the assembly: Whether the fittings are installed correctly, whether they meet the electrical schematic diagram, and the wiring diagram requirements, whether the electrical conductivity is good.
3. Safety inspection: There are two main aspects to the safety inspection of electronic products, insulation resistance and insulation strength.
45. Try to compare the similarities and differences between process documents and design documents.
The process document and the design document are the same documents for guiding production. The design document is the original document and is the basis for production. The process document is based on the processing method proposed by the design document to realize the requirements on the design drawing and the process specification and the whole machine process. The document drawings know the production to ensure the smooth completion of the task.
46. ​​What are the principles and requirements for the preparation of process documents?
1. Compilation principles:
The corresponding process documents are compiled according to the batch size, performance index and complexity of the product.
The technical documents are woven according to the equipment conditions of the enterprise, the technical level of the workers and the organization of the production.
The process documents should be easy to read and easy to read based on the drawings. If necessary, you can live with simple text instructions.
The contents of the technical procedures that should be known to the dispatcher should not be included in the process documentation.
2. Requirements:
1 The preparation of electronic process documents is done according to the specific conditions of the products produced, in accordance with certain specifications and formats; in order to ensure the smooth progress of production, the completeness of the process documents should be ensured and compiled according to certain specifications and format requirements. book.
2 The name, symbol, number, figure number, material, component code, etc. used in the process documents shall comply with the national standard or the department standard. Writing should be standardized, neat, and the graphics should be drawn accurately and proportionally.
3 In the process documents, the general technical conditions, technical rules, or enterprise standard technical procedures shall be quoted as much as possible, and the tools, special tools and test equipment shall be effectively used.
4 When preparing the process procedures for key processes and important parts, the process requirements, precautions, models and methods of use of various instruments and equipment used in each process shall be written in detail.
47. What are the requirements for the development of the commissioning process documentation and the requirements for the commissioning process plan?
49. What are the working principles of the commissioning process?
Principle: 1 Debug the power supply first, and then debug other parts of the circuit. 2 Move first and then move. 3 Block debugging 4 First circuit debugging, after the mechanical part debugging.
What are the commonly used methods for 50 static tests? And make a brief introduction.
Divided into direct debugging method and indirect debugging method.
Direct debugging: It is a method of disconnecting the circuit under test and conducting current test in the current circuit of the current meter or multimeter.
Indirect debugging: A method that can be indirectly tested by measuring the voltage first and then converting it into a current.
51. Briefly introduce the general method of debugging fault finding and processing.
Observation method, measurement method, signal method, comparison method, replacement method, heating and cooling method, computer intelligent automatic detection,
52. What is the essentials of ferrochrome soldering?
1. Prepare for welding
2. Master the method of soldering iron solder joints and the method of supplying solder.
3. Choose the right electric iron car evacuation method
4. Master the proper welding time and temperature
5. After the welding, clean the welder around the solder joint and check for defects such as flaws, mis-welding and solder joints.
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