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The Difference Between Gold Plating And ENIG

Le 14 juin 2017, 18:33 dans enepig pcb 0

The surface of the circuit board has several processes: Bare PCB (surface without any treatment), Rosin board, OSP (organic solder preservative, slightly better than rosin), HASL (a tin, lead free tin), gold plating, ENIG(Electroless Nickel/Immersion Gold), which is more common. We briefly introduce the difference between gold plating and ENIG.

ENIG is a method of chemical deposition, and a layer of coating is formed by chemical oxidation-reduction reaction. The thickness of the deposit is thicker, which is one of the chemical nickel, gold and gold layer deposition methods, which can reach a thicker gold layer.

Gold plating uses the principle of electrolysis, also known as electroplating. Most other metal surface treatments are plated.

In the actual product applications, 90% of the gold boards are the ENIG, because the poor weldability of the gold-plating is his fatal flaw, but also a direct cause of many companies to abandon the gold-plating process.

ENIG of printed circuit surface is stable color, good brightness, good coating and good weldability. Basically can be divided into four stages: pretreatment (degreasing, micro corrosion, activation, after immersion), immerse nickel, immerse gold, end treatment (waste gold washing, DI washing, drying). The thickness of ENIG is between 0.025-0.1um.

Gold used in circuit board surface treatment, because the conductivity of gold is strong, good oxidation resistance, long life, general applications such as key board, finger board, etc. The fundamental difference between gold plating and ENIG is gold plating is hard gold (hard wearing), ENIG is soft gold (not hard wearing).
Difference between gold plating and ENIG:

    * As the circuit board processing requirements are higher and higher, the line width and spacing have reached below 0.1mm. Gold plating is easy to produce gold wire short circuit. The ENIG only has nickel gold on the pad, so it is not easy to produce a gold wire short circuit.
    * The crystal structure is more dense of ENIG compare gold plating, so it is difficult to produce oxidation.
    * The ENIG only has nickel gold on the pad compare gold plating. In the skin effect, the signal transmission is in the copper layer, which will not affect the signal.
    * ENIG and gold plating crystal structure is not the same, It required thicker gold for ENIG than gold plating,and the gold will be golden yellow than gold plating,which is recognition method of ENIG and gold plating,the gold is slightly pale of gold plating like nickel color.
    * ENIG and gold plating crystal structure is different,ENIG is easier to weld, will not cause welding bad. The     stress of the ENIG is easier to control, and it is more conducive to the processing of the bonding products. At the same time, it is because the gold deposit is more soft than the gold plating. Therefore, the gold finger of ENIG is not wearable (the disadvantages of the ENIG).
    * The ENIG only has nickel gold on the pad. Therefore, the solder mask on the line is more firmly integrated with the copper layer. It will not affect the spacing when it is compensated.
    * For higher requirements of flatness PCB, generally used ENIG, ENIG generally does not appear black pad phenomenon after assembly. The flatness and longevity life of ENIG is better than gold plating.

So most factories now use ENIG process to produce gold PCB. But the ENIG process is more expensive than the gold plating process (higher gold content), so there are still a large number of low-priced products using gold plating process (such as remote control board, toy board).

PCB Failure Analysis Method

Le 6 juin 2017, 18:51 dans pcb 0

PCB circuit board has become the most important part of electronic products as its carrier of various components and signal transmission,PCB quality and reliability determines the quality and reliability of the whole machine.

With the miniaturization of electronic products and environmental protection requirements of lead-free and halogen-free,PCB also develops towards high-density, high Tg and environmental protection.However, due to cost and technical reasons, a large number of failures have been occurred in the production and application of PCB, and many quality disputes have been triggered.In order to find out the cause of the failure and to find a solution to the problem and to distinguish responsiblility,failure analysis of failure case must be carried out.

Basic procedures for failure analysis

To obtain PCB circuit board failure or poor accuracy or mechanism, must abide by the basic principle and the analysis process, otherwise the failure may miss valuable information, analysis can not continue or might get the wrong conclusion caused. The basic process is generally must first be based on the failure phenomenon, through the collection of information, function test, electrical performance test and simple visual inspection, determine the failure position and failure mode, the failure location or fault location.

For simple PCB or PCBA, the failure of the site is easy to determine, but for the more complex BGA or MCM package devices or substrate defects through the microscope, the moment is not easy to determine, this time need to be determined by other means.

Then it is necessary to analyze the failure mechanism, namely the use of various physical and chemical means to analyze the mechanism leading to PCB failure or defects, such as solder, pollution, mechanical damage, moisture stress, corrosion and fatigue damage, CAF or ionic migration, stress overload etc..

Then analyze the reasons for the failure, the failure mechanism and process based on process analysis, find the cause of the failure mechanism of the test should be carried out as necessary, general test may, through the test can find the reason of failure induced by the accurate.

This provides a definite basis for the next step of improvement. Finally, according to the analysis process to obtain test data, facts and conclusions, the preparation of failure analysis report, the requirements of the report of the facts clear, logical reasoning, strict, coherent, and should not be imagined.

In the process of analysis, attention should be paid to the basic principles of analytical methods, from simple to complex, from outside to inside, from never destroying samples to using them. Only in this way can we avoid losing the key information and avoid introducing new artificial failure mechanism.

The failure analysis of PCB or PCBA is the same. If an electric iron is used to repair the missing solder joints or to shear the PCB strongly, then the analysis cannot be done. The failure site has been destroyed. Especially in the case of less failure samples, once the damage or damage to the site of the environment, the real failure reason can not be obtained.

Failure analysis technique

1.Optical microscope

The optical microscope is mainly used for the appearance inspection of PCB, looking for the failure parts and relevant material evidence, and preliminarily judging the failure mode of PCB. The appearance inspection mainly examines the PCB pollution, corrosion, bursting plate location, circuit wiring and failure regularity, such as batch or individual, whether it is always concentrated in a certain area and so on.

2.X ray

For certain parts that cannot be visually examined, as well as through and through the hole and other internal defects of the PCB, the X ray fluoroscopy system is used. X-ray system is the use of different materials, thickness or density of different materials to X light moisture absorption or transmittance of different principles to imaging. This technique is used to check the internal defects of PCBA solder joints, the defects in through holes and the defects of BGA or CSP devices in high-density packaging.

3.Slice analysis

Slice analysis is the process of obtaining PCB cross section structure by means of sampling, mosaic, slicing, grinding, etching and observation. Through slicing analysis, we can get abundant information about microstructure of PCB (through hole, plating, etc.), and provide a good basis for quality improvement in the next step. But the method is destructive, and once it is sliced, the sample is bound to suffer damage.

4.Scanning acoustic microscope

At present, for the analysis of electronic packaging or assembly is mainly ultrasound scanning acoustic microscope C mode, which is reflected in the material discontinuous interface using high frequency ultrasonic amplitude and phase and polarity changes to imaging, its scanning mode is along the Z axis scanning X Y plane information.

Therefore, scanning acoustic microscopy can be used to detect defects in components, materials, and PCB and PCBA, including cracks, delamination, inclusions, voids, and so on. If the frequency of the scanning acoustic is sufficient, the internal defects of the solder joint can also be detected directly.

The typical image scanning acoustic is the red warning color represents the existence of defects, due to the large number of plastic packaging components used in the SMT process, by a lead into a lead-free process in the process of a large number of wet reflux sensitive issues, namely the internal moisture of plastic devices or substrate delamination phenomenon in lead-free reflow higher process temperatures, common in high temperature lead-free process under the PCB will often appear in the phenomenon of explosion.

At this point, scanning acoustic microscopy has highlighted its special advantages in multi layer high-density PCB nondestructive testing. In general, the obvious burst plates can be detected only by visual inspection.

5.Micro infrared analysis

FTIR analysis is infrared spectroscopy and microscopy analysis together, using different materials (mainly organic) different absorption principle of the infrared spectrum analysis, compound material, combined with the microscope can make visible light and infrared light, as long as in the field, you can find the analysis the trace organic pollutants.

If there is no combination of microscopes, the infrared spectrum can usually be used to analyze samples with more samples. And in the electronic process, a lot of situations are micro pollution, which can lead to the poor weldability of the PCB welding pad or lead pin. It can be imagined that it is difficult to solve the process problem without the infrared spectrum provided by the microscope. The main purpose of micro infrared analysis is to analyze the organic contaminants in the welded surface or solder joint surface, and to analyze the cause of poor corrosion or weldability.

6.Scanning electron microscope analysis (SEM)

Scanning electron microscope (SEM) is one of the most useful failure analysis of large electron microscopic imaging system, the most commonly used morphology observation, scanning electron microscopy, the function is very powerful, any fine structure or surface characteristics can be enlarged to hundreds of thousands of times were observed and analyzed.

The failure analysis of PCB or SEM solder joints, mainly used for the analysis of the failure mechanism, specifically is used to observe the pad surface morphology, microstructure, solder joint measurement of intermetallic compound, solderable coating and analysis of tin whisker measurement and analysis etc..

Different with the optical microscope, scanning electron microscope and the electron is like, so only black and white, and the scanning electron microscope sample requirements for non conductive conductor and semiconductor part need to spray gold or carbon, or charge accumulation on the surface of the sample on the influence of sample observation. In addition, the depth of image of scanning electron microscope is much larger than that of optical microscope. It is an important analysis method for metallographic structure, micro fracture and tin paste.

7.Thermal analysis

Differential scanning calorimetry (DSC)

Differential Scanning Calorimetry is a method of measuring the relationship between the power difference between a substance and reference material and temperature (or time) under programmed temperature control. It is a method to study the relationship between heat and temperature. According to this change relation, the physical, chemical and thermodynamic properties of materials can be studied and analyzed.

DSC is widely used, but in the analysis of PCB is mainly used for curing degree, glass transition temperature conversion of various high polymer materials used to measure the PCB, the two parameter determines the reliability of the PCB in the follow-up process.

8.Thermal mechanical analyzer (TMA)

Thermal Mechanical (Analysis) is used to measure the deformation properties of solids, liquids, and gels under thermal or mechanical forces for program temperature control. It is a method to study the relationship between heat and mechanical properties. According to the relationship between deformation and temperature (or time), the physical, chemical and thermodynamic properties of materials can be studied and analyzed.

TMA is widely used in PCB analysis. It is mainly used for the two key parameters of PCB: measuring its linear expansion coefficient and glass transition temperature. The PCB of the base material with excessive expansion coefficient often results in fracture of the metallized hole after welding assembly.

9.Thermogravimetric analyzer (TGA)

Analysis (Thermogravimetry) is a method of measuring the relationship between the mass of a substance with temperature (or time) under programmed temperature control.

How To Quick Find PCB Defects?

Le 1 juin 2017, 15:55 dans pcb defects 0

PCB is printed circuit board,it mechanically supports and electrically connects electronic components using conductive tracks,pads and other features etched from copper sheets laminated onto a non-conductive substrate,achieve electronic components automated assembly,welding,inspection,guaranteed the quality of electronic devices,improved productivity and reduced the cost,it’s favorable for repair.

PCB from single layer to multilayer,flex,keep ourselves strong development.These years tend to high precision,high density,high reliably and small size to reduce cost and improve functions,PCB industry keep strong vitality in future electronic devices development.

Analysis of PCB board common defects

Various defects happened in usage follow PCB circuit complicate and components integrated.We summarized four common defects:

    The PCB layout is inappropriate,electromagnetic interference from around components.
    PCB circuit damage lead to system out of work.
    Components unsteadiness lead to device unstable.
    Incomplete welding lead to PCB board opening or short.

Works before PCB board inspection

    Know about the environment of device working,main the electric parameter impact from external environment.
    Inquiry the phenomenon led to PCB board failure and analysis the reasons caused.
    C. Check up carefully components of PCB board,find out the important components.
    D. Do the electrostatic prevention and electromagnet interference prevention measure.
    PCB board inspection process and rules.

The PCB board inspection flow chart.

The flow chart indicated common process,from graphic we know the first step is inspect PCB structure and appearance,then make test for the important discrete components and IC integrated circuit.Repair or replace failure components after found out defect parts,use instrument to re-test PCB.The discrete components,IC integrated circuit is the most important parts,we understand the flow chart into four items:from observe to measure,from outside to inside,from easy to complicated ,from static to dynamic.

1.From artificial observation to instrument measure

All components connected by surface circuit in PCB, So the fist thing we can observe appearance by magnifier or microscope when it happened errors.

    Whether all components connected completely? If power and ground position can work.
    Whether pins are correct welding of integrated chip,diode,BJT,resistance,capacitor,inductance etc.
    Whether components have incomplete weld,miss welding and other operation problems.

Most damages can find through above initial observation and differentiate. But some defects can’t be discover by naked eyes,then need use multimeter to check.The normal impedance is 70~80 ohm between ground and power layer, if the value is too small meant some components perhaps be punctured,then we must find out the parts be punctured.In general we touch the burning hot parts and find out damages when power cord works. If the parts works then we need check and debug each components compared input and output parameter .

2.From outside to inside

The ratio failure components lead to PCB defects is large from above analysis,so how to find out the failure components is very important.As PCB structure feature,the components at outside of edge are easy damage,the ratio reach 86%.Components at outside major used in driver,inverter,isolation,protecting and communication for easy connection with inner circuit.They always be impacted from current surging,vibrating and external power lead to noise and dust,thus failure happened to this outside components.Components placed inside are major used in generate,amplify,transmit signal.Check the inside components after eliminated components at outside.

3.From easy to complicated

There related some test technology in PCB inspection,we follow rules:from easy to complicated in checking process.

a.The works before PCB test

Circuit Simulation is an effective way to reduce design period and cost.But simulation is in perfection condition ,it ignored all interferences at actually works,so shield all interferences before test is necessary.In general way shielding interferences is short of crystal oscillator and dismantle CUP avoid testing hamper.

b.From easy to complicated in special test way

We use rule “from easy to complicated “way to check components,because easy components can easy find out problems. We use exclusive method to check it one by one and record it.Retest that error caution PCBs to guarantee accuracy. We consider it important suspect for the PCBs failed test.

c. Complementary test method between different method

Sometimes we can’t find out the problem if only use one test way.we need use all kinds of test method to check from easy to complementary, now PCB test way from MVI,ICT to BST, and now more new test technology apply in PCB test.

4.From static to dynamic

All the methods above mentioned multimeter and other methods are static inspection.But sometimes the reason is very complicated and we can’t diagnose in static status.We use multimeter to check when power is on if static inspection can’t work.Integrated IC always use this method to check.

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