Parameters and principles of electronic components selection tutorial

"Great oaks from little acorns grow", laying a good foundation is the key to do a good job.??For a motherboard, from the design to the selection of each component is an important step to determine the product.??Sorted out some electronic components selection experience to share, hoping to provide help to you.??Qiyang intelligent ARM embedded development?

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Basic principles of component selection:?

A) Principle of universality: if the selected components have been widely used and verified, they should use less unpopular and biased chips to reduce development risks.?

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B) High cost performance principle: in the case of similar functions, performance and utilization rate, try to choose components with relatively good prices to reduce costs.?

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C) Principle of convenient procurement: try to choose components that are easy to buy and have a short supply cycle.?

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D) Principle of sustainable development: try to select components that will not be discontinued in the foreseeable time.?

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E) Principle of substitution: Try to select components with more brands of PIN-to-PIN compatible chips.?

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F) Upward compatibility principle: try to select components used in previous products.?

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G) Resource conservation principle: use all functions and pins of components as much as possible.?

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Comprehensive consideration?

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01, easy to produce application reliability problems of the device?

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A device that is sensitive to external stress?

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CMOS circuit: sensitive to static electricity, latch, surge?

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Small signal amplifier: sensitive to overvoltage, noise and interference?

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Plastic package device: sensitive to moisture, thermal shock, temperature cycle?

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A device whose operating stress approaches the maximum stress of the circuit?

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Power device: The power is close to the upper limit?

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High voltage devices: Voltage close to the upper limit?

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Power supply circuit: Voltage and current close to limit value (power supply)?

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High frequency devices: frequency near limit (RF and high speed digital)?

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Ultra large scale chip: power consumption close to the limit (especially high-power CPU, FPGA, DSP, etc.)?

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Devices with high frequency and power?

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Clock output circuit: the highest frequency in the entire circuit, and to drive almost all digital circuit modules?

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Bus control and driving circuit: driving ability, high frequency?

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Transmitters in wireless transceiver circuits: power and frequency near limits?

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02, the selection of components to consider the ten elements?

1, electrical characteristics: in addition to meeting the functional requirements of equipment, components should be able to withstand the maximum applied electrical stress.?

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2. Operating temperature range: the rated operating temperature range of the component shall be equal to or wider than the operating temperature range to be subjected to.?

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3. Process quality and manufacturability: the process of components is mature and stable and controllable, the yield should be higher than the specified value, and the packaging should be compatible with the equipment assembly process conditions.?

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4. Stability: In the case of temperature, humidity, frequency, aging and other changes, the parameters change within the allowed range.?

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5. Life: the working or storage life shall be no less than the expected life of the equipment in which they are used.?

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6. Environmental adaptability: It should be able to work well in various environments, especially in special environments such as hot flashes, salt spray, dust, acid rain, mold, radiation and high altitude.?

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7. Failure mode: The typical failure mode and failure mechanism of components should be fully understood.?

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8. Maintainability: The convenience of installation, disassembly and replacement should be considered, as well as the required tools and proficiency level.?

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9. Availability: there is more than one supplier, the supply cycle can meet the equipment manufacturing schedule, and timely replacement requirements can be guaranteed when components fail.?

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10. Cost: Consider using cost-effective components on the condition that they can simultaneously meet the required performance, life and environmental constraints.?

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03. Failure mode and its distribution?

Failure mode: the failure mode of the component, i.e. how it failed??

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Failure mechanism: the failure reason of the component, i.e. why it failed??

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Component users should understand failure modes, if not failure mechanisms.?

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Failure mode distribution: If a component has multiple failure modes, the probability of each failure mode is the premise of failure analysis.?

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04. Characteristics of highly reliable components?

Manufacturer certification: the manufacturer has passed the qualification certification of the authority?

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Production line certification: products can only be certified in the special production line production.?

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Reliability testing: The product has been subjected to and passed a series of performance and reliability tests, 100% screening and quality consistency testing.?

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Process control level: the production process of products has been strictly controlled, high yield.?

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Degree of standardization: the production and inspection of products conform to international, national or industrial general specifications and detailed specifications.?

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05. Preferential selection rules for varieties and models?

1. Give priority to standard, general and serialized components, carefully select new varieties and non-standard components, and minimize the variety and specifications of components and the number of manufacturing units.?

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2. The components should be listed in the preferred directory.?

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3. Priority should be given to products with mature device manufacturing technology, and fixed-point suppliers with long-term, continuous, stable, mass supply and high yield should be selected.?

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4. It is preferred to choose products from manufacturers that can provide perfect process control data, reliability application guidelines or use specifications.?

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5. On the premise of the same quality grade, the devices with high integration degree should be selected first, and discrete devices should be selected less.?

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06. Reliability information provided by the supplier?

Detailed specifications and standards: national military standard, national standard, line standard, enterprise standard?

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Certification: QPL, QML, PPL, IECQ, etc?

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Quality grade and reliability level: failure rate, life (MTTF), anti-static strength, anti-irradiation level, etc?

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Reliability test data: acceleration and field, environment and life, recent and past, test methods and data processing methods used?

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Yield data: medium test (naked), total test (after packaging), etc?

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Quality consistency data: batch to batch, wafer to wafer, chip to chip, mean, variance, distribution?

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Process stability data: statistical process control (SPC) data, batch production?

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Processes and materials used: it is best to provide the main parameters of key processes and materials?

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User manual and operation specification: typical application circuit, reliability protection method, etc?

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Process to consider?

Take integrated circuits as an example:?

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Minimum line: 0.35, 0.25, 0.18, 0.13μm?

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Substrate material: Si>SOI>SiGe>GaAs>SiC?

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Interconnect material: Cu>Al (foreign advanced process) Al>Cu (domestic existing process)?

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Passivation material: SiN>PSG> polyimide inorganic > organic?

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Bonding material: Au>Cu>Al(Si)?

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Circuit form: number/module separation > number/module integration RF/BB separation >RF/BB integration?

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The relationship between CMOS chip yield and reliability?

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Yield (sometimes referred to as quality) : The number of qualified devices found in batch devices during outgoing or aging screening.?

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Reliability: the number of failed devices after more than one year of on-board time.?

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Generally speaking, the higher the quality and yield of the device, the better the reliability;??However, the reliability of devices with the same quality and yield is not exactly the same.?

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SPC data: characterization of pass rate?

Statistical process control?

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Process accuracy and Process stability are important factors to determine product yield and reliability, which can be quantitatively characterized by SPC data.?

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Characterization parameters of pass rate?

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Yield: Percentage of qualified product in batch.?

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PPM (parts per million) : the number of unqualified products per million products, suitable for large batch, stable quality, high yield product characterization.?

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Characterization of process deviation and dispersion:?

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The production of nonconforming products mainly comes from the inevitable deviation and dispersion of component manufacturing process, and the distribution of process parameters usually meets the normal distribution.?

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Encapsulation consider?

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01. Typical values of parasitic parameters?

Pin components: Parasitic inductance 1nH/mm/ pin (shorter is better), parasitic capacitance 4pF/ pin?

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Pin less components: parasitic inductance 0.5nh/port, parasitic capacitance 0.3pF/ port?

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Comparison of parasitic effects of different packaging forms (parasitic parameters from small to large)?

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No pin mount > Surface mount > radial pin > axial parallel pin?

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CSP>BGA>QFP>SMD>DIP?

The parasitic inductance of the capacitor is also related to the packaging form of the capacitor.??The larger the pin aspect ratio is, the smaller the parasitic inductance is.?

02, conducive to reliability?

Extremely short leads: reduced distributed inductance and capacitance, improved anti-interference ability and circuit speed?

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High mechanical strength: improve the resistance of the circuit to vibration and impact?

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Good assembly consistency: high yield, small parameter dispersion?

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03. Bad for reliability?

Increased material mismatches: The thermal expansion coefficient of SMT elements on some ceramic substrates (such as some resistors, capacitors, leadless chip carrier LCC) does not match that of epoxy glass on PCB substrates, resulting in thermal stress failure?

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Easy contamination: it is not easy to clean between SMT components and PCB boards, and the contaminants that reside in flux easily need special treatment?

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Surface mount is far more beneficial than harmful to reliability, accounting for 90% of the current?

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04. Comparison of packaging materials?

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Plastic package?

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Advantages: low cost (about 55% of the ceramic package), light weight (about 1/2 of the ceramic package), more pins, weak high-frequency parasitic effect, easy to automatic production.?

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Disadvantages: poor air tightness, moisture absorption, not easy to heat, easy aging, sensitive to static electricity.?

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Applicability: most semiconductor discrete devices and integrated circuit conventional products.?

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Ceramic packaging?

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Advantages: good air tightness, heat dissipation ability (high thermal conductivity), high frequency insulation performance, withstand large power, high wiring density.?

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Cons: High cost.?

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Applicability: aviation, aerospace, military and other high-end markets.?

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Metal packaging?

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Advantages: good air tightness, heat dissipation ability, electromagnetic shielding ability, high reliability.?

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Disadvantages: high cost, limited number of pins.?

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Applicability: small scale highly reliable devices.?

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Usually called plastic sealing for non - gas - tight packaging, ceramic and metal for gas - tight packaging.?

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Moisture absorption problem?

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The epoxy resin material used in plastic packaging has moisture absorption and moisture is easily adsorbed on its surface.?

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Water vapor will cause the plastic material itself creep, such as intrusion into the chip, will lead to corrosion and surface contamination.?

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Air tightness problem?

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Lead frame, plastic shell and metal materials such as semiconductor chips of the thermal expansion coefficient difference is much larger (compared with ceramic and metal shell) and the temperature change will generate considerable mechanical stress in the material interface - interface feature - degradation in air tightness Water gathered in aperture place - temperature rises rapidly vaporized and expansion to further intensify the interface stress, there is??Can make the plastic shell burst (" popcorn "effect)?

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During PCB reflow welding, the temperature can rise to 205 ~ 250 ℃ within 5 ~ 40s with a gradient of 1 ~ 2 ℃/s, which is easy to produce the above effects.?

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Temperature adaptability problem?

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The glass conversion temperature of the plastic sealing material is 130 ~ 160 ℃, beyond which the plastic sealing material will soften, and has an adverse effect on the air tightness.?

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The temperature range of commercial plastic sealing devices is generally 0~ 70 ℃, -40~+85 ℃, -40~+ 125℃, and it is difficult to reach the military temperature range of -55~+125 ℃.?