Electronic component selection parameters and principles

For a motherboard, the design to the selection of each component is an important step in determining the product. This article compiles some of the electronic components selection experiences to share, and I hope to help you.

 

Component selection basic principles

(a) the principle of universality: the selected components are widely used and verified, as little as possible to use the cold, off-chip, reduce the risk of development.

(b) cost-effective principle: in the case of similar functions, performance, and utilization rate, try to choose the components with better prices to reduce costs.

(c) procurement convenience principle: try to choose components that are easy to buy and have a short delivery cycle.

 

(d) the principle of sustainable development: try to choose the components that will not be discontinued in the foreseeable time.

 

(e) the principle of substitutability: try to choose the pin-to-pin compatible chip brand components.

 

(f) the principle of upward compatibility: try to choose the components used in previous old products.

 

(g) the principle of resource conservation: try to use all the functions and pins of the components.

 

Careful consideration

 

01、Devices prone to application reliability problems

Devices sensitive to external stress

CMOS circuits: sensitive to static electricity, latch-up, and surges

 

Small signal amplifier: sensitive to overvoltage, noise, interference

 

Plastic package devices: sensitive to moisture, thermal shock, temperature cycling

 

Devices with operating stress close to the maximum stress of the circuit

 

Power devices: power close to the limit

 

High voltage devices: voltage close to the limit

 

Power circuits: voltage and current close to the limit value (power supply)

 

High-frequency devices: frequency close to the limit value (RF and high-speed digital)

 

Super-scale chips: power consumption close to the limit value (especially high-power CPUs, FPGAs, DSPs, etc.)

 

Devices with high frequency and power

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

 

Bus control and drive circuit: high drive capability and high frequency

 

The transmitter in wireless transceiver circuit: power and frequency close to the limit value

 

02、The selection of components to consider the ten elements

1, electrical characteristics: components should be able to withstand the maximum applied electrical stress and meet the equipment's functional requirements.

 

2. operating temperature range: the rated operating temperature range of the components should be equal to or wider than the operating temperature range to be withstood.

 

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

 

4. stability: in the case of changes in temperature, humidity, frequency, aging, etc., the parameters change within the allowed range.

 

5. life: working or storage life should not be shorter than the expected life of the equipment using them. 6.

 

6. environmental adaptability: should be able to work well in various use environments, especially such as hot and humid, salt spray, sand and dust, acid rain, mold, radiation, high altitude, and other special environments.

 

7. failure mode: The components' typical failure mode and failure mechanism should be fully understood.

 

8. maintainability: should consider the ease of installation, disassembly, replacement, and the required tools and skill level.

 

9. availability: more than one supplier, supply cycle to meet the equipment manufacturing schedule, to ensure the timely replacement of components failure requirements, etc. 10.

 

10. Cost: Consider the use of cost-effective components under the condition that the required performance, life, and environmental constraints can be met.

 

03、Failure mode and its distribution

Failure mode: the failure form of components, that is, how to fail?

 

Failure mechanism: the cause of failure of components, that is, why the failure?

 

Component users should understand the failure mode even if they cannot understand the failure mechanism.

 

Failure mode distribution: If the component has multiple failure modes, the probability of various failure modes is a prerequisite for failure analysis.

 

04、Characteristics of highly reliable components

Manufacturer certification: The manufacturer has passed the qualified certification by the authority

 

Production line certification: The product can only be produced on a certified and qualified dedicated production line.

 

Reliability inspection: The product is conducted and passes a series of performance and reliability tests, 100% screening, and quality consistency inspection.

 

Process control level: The product's production process is strictly controlled, and the finished product rate is high.

 

Standardization level: The production and inspection of the products meet the requirements of international, national, or industry general specifications and detailed specifications.

 

05、 Preferential selection rules of varieties and models

1. Priority is given to standard, common and serial components. New varieties and non-standard devices are carefully selected to maximize the compression of the number of varieties and specifications of components and the number of manufacturing units.

 

2. Priority is given to including the component's preferred directory.

 

3. Give priority to using devices with mature manufacturing technology, long-term, continuous, stable, high-volume supply, and a high rate of finished product point of delivery units.

 

4. Priority is given to manufacturers who can provide perfect process control data, reliability application guidelines, or use specifications.

 

5. On the premise of comparable quality level, prioritize the devices with high integration degrees and less discrete devices.

 

06. Reliability information to be provided by the supplier

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

 

The quality level and reliability level: failure rate, lifetime (MTTF), anti-static strength, irradiation resistance level, etc.

 

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

 

Yield data: mid-test (die), total test (after packaging), etc.

 

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

 

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

 

Processes and materials used: key parameters of key processes and materials are desirable.

 

Manuals and operating specifications: typical application circuits, reliability protection methods, etc.

 

Process considerations

Using integrated circuits as an example.

 

Minimum line: 0.35, 0.25, 0.18, 0.13μm

 

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

 

Interconnection material: Cu>Al>Cu

 

Passivation material: SiN>PSG>Polyenimine Inorganic>Organic

 

Bonding material: Au>Cu>Al(Si)

Circuit form: digital/analog separation>digital/analog integration RF/BB separation>RF/BB integration

Relationship between CMOS chip yield and reliability

Yield rate (sometimes called quality): the number of qualified devices found in a batch device during factory or aging screening.

Reliability: The number of failed devices after more than one year.

Generally speaking, the higher the quality and yield of the device, the better the reliability; however, the reliability is not the same for devices with the same quality and yield.

 

Statistical Process Control

Process accuracy and process stability are important factors in determining product yield and reliability and can be quantitatively characterized by statistical process control (SPC, StaTIsTIcal Process Control) data.

 

Characterization parameters of yield

Yield: The percentage of qualified products in a batch.

Ppm (parts per million): the number of non-conforming products per million, suitable for characterizing products with large batches, stable quality, and high yield.

 

Characterization of process deviations and dispersions.

Non-conforming products are mainly generated from the inevitable deviations and dispersions in the component manufacturing process, and the distribution of process parameters usually satisfies a normal distribution.

 

Packaging considerations

01. Typical values of parasitic parameters

Pinned components: parasitic inductance 1nH/mm/ pin (the shorter the better), parasitic capacitance 4pF/ pin

 

Pinless components: parasitic inductance 0.5nH/port, parasitic capacitance 0.3pF/port

 

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

 

Pinless mount > Surface mount > Radial pin > Axial parallel pin

 

CSP>BGA>QFP>SMD>DIP

The parasitic inductance of a capacitor is also related to the package form of the capacitor. The larger the pin width to length ratio, the smaller the parasitic inductance.

 

02、Beneficial to reliability

Extremely short lead wires reduce distributed inductance and capacitance and improve anti-interference capability and circuit speed.

 

High mechanical strength improves the circuit's ability to resist vibration and shock.

 

Good assembly consistency: high yield and small parameter dispersion

 

03. Detrimental to reliability

Increased material mismatch: certain ceramic substrate SMT components (such as certain resistors, capacitors, leadless chip carriers LCC) do not match the thermal expansion coefficient of the epoxy glass of the PCB substrate, triggering thermal stress failure

 

Easier to contaminate: SMT components and PCB boards between not easy to clean, easy to reside in the pollutants of solder, and need to use special processing methods

 

Surface mount on reliability is far more advantageous than disadvantageous, currently has accounted for 90% of the proportion.

 

04. Comparison of package material

Plastic package

Advantages: low cost (about 55% of the ceramic package), lightweight (about 1/2 of the ceramic package), the number of pins, the high-frequency parasitic effect is weak, and convenient for automated production.

 

Disadvantages: poor hermeticity, moisture absorption, not easy to dissipate heat, easy aging, sensitivity to static electricity.

 

Applicability: Most semiconductor discrete devices and integrated circuit conventional products.

 

Ceramic package

Advantages: good airtightness, good heat dissipation (high thermal conductivity), high-frequency insulation, high power, and high wiring density.

 

Disadvantages: high cost.

 

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

 

Metal package

Advantages: good airtightness, strong heat dissipation, electromagnetic shielding capability, and high reliability.

 

Disadvantages: high cost, a limited number of pins.

 

Applicability: Small-scale, highly reliable devices.

 

Usually called plastic package as non-hermetic package, ceramic and metal as a hermetic package.

 

Moisture absorption problem

The epoxy resin material used in the plastic package is inherently moisture-absorbing, and moisture is easily adsorbed on its surface.

 

Moisture can cause creep of the plastic package material itself, which can lead to corrosion and surface staining if it invades the chip.

 

Air tightness problem

Plastic shell and metal lead frame, semiconductor chips, and other materials, the difference in coefficient of thermal expansion is much larger (compared with ceramic and metal shell) → temperature changes in the material interface will generate considerable mechanical stress → interface gaps → resulting in airtightness degradation Water vapor gathered in the gap → rapid vaporization and expansion when the temperature rises → interface stress further increased → might make the plastic seal burst ( "popcorn" effect)

 

PCB reflow soldering temperature can rise to 205 ~ 250 ℃ in 5 ~ the 40s, rising gradient to 1 ~ 2 ℃ / s, easy to produce the above effect.

 

Temperature adaptability issues

The glass transition temperature of the plastic sealing material is 130-160 ℃, beyond which the plastic sealing material will soften and hurt the air tightness.

 

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