Can you assess a PCB's similarity to its golden sample just

2019-12-02 16:32Writer: qyadminReading:
         Since components and leads get smaller over time. this specific becomes difficult and almost impossible when considering worldwide PCB fabrication. How provides visual inspection of PCBs evolved?
  Visual inspection of PCBs is definitely an essential part of the producing process. Technological advancements during the last several decades, but, make visual inspections more exact. and in some cases eliminated humans through the picture .
       Here's a high-level appearance at some examples of these advancements in action.
 
 

     What Is a Golden Sample?

 
  A "golden sample" is actually a manufactured sample regarded . as the best embodiment of the design as that intended. It is usually a "perfect" or "ideal" example of a tool or PCB that is a new bar against. which to measure all other fabricated samples. Using a golden sample. to ensure top quality for fabricated PCBs requires intensive attention to detail. coming from the skew of elements on the board for the integrity of leads on a QFN package.
  A gold sample can benchmark elements including those. that could measured by oscilloscopes. and other ensure that you way of measuring equipment. Visual inspection, but, is also important for pinpointing errors inside the fabrication process. Modern visual inspection usually contains the use of microscopes. Apps designed to job with these microscopes. intended to further aid in board assessment in improving in popularity. Also popular is AOI or automatic optical inspection. which utilizes a camera to do independent inspections of PCBs in post-production.
 
     All these kinds of methods involve a form of photogrammetry.  the term for computing objects based off of photographs taken of them. While this term can applied to dimensions of, say. buildings or natural formations based about aerial photography. it also applies to the way of measuring of PCB features on the scale of microns.

      Businesses and consumers alike. rely on electronic devices for every aspect of day-to-day life. Automobiles  packed full of printed circuit boards (PCBs) for everything from lighting. and entertainment to sensors that control the behavior of critical mechanical functions. Computers, tablets, smartphones. and even many toys enjoyed by children incorporate electronics. and PCBs for their sophisticated functionality.
 
      PCB designers today  challenged to create reliable boards that perform  complex functions. while controlling costs and shrinking in dimension. This is especially critical in applications such as smartphones, drones. and other applications where weight is a critical consideration in the PCB characteristics.
 
      Gold is an important element. in the design of printed circuit boards, and looking  at most PCBs will reveal. that the ‘fingers’ on the board include metal contacts fabricated from gold. These fingers are  multi-layered metals that may include materials. such as tin-lead, cobalt, or nickel, plated with a final layer of gold. These gold contacts are critical to the functionality of the resulting PCB. establishing the connection with the product containing the board.

PCB gold application

 
      Attributes of gold make it an excellent choice for use in PCB fabrication. Edge connectors plated with gold provide a consistent surface finish for applications. that subjected to high-wear such as board insertion edge points. Hardened gold presents a stable surface quite resistant to wear from. such repeated activity.
 
      By its very nature, gold suited for electronics applications:
 
      It formed and manipulated for connectors, wires, and relay contacts
Gold conducts electricity very (an obvious need for PCB applications)
 
      It can carry small amounts of current, essential for today’s electronic devices
Other metals can alloyed with gold such as nickel or cobalt
 
      It does not tarnish or corrode, making it a reliable connection medium
Melting and reclaiming gold for reuse is a simple process
 
       Only silver and copper provide higher conductivity properties. but each of them are prone to corrosion, generating current resistance
Even thin applications of gold can provide reliable. and stable contacts with low resistance
Gold connections can tolerate high temperatures
Variations in thickness can utilized to meet the requirements of specific applications
every electronic device contains some level of gold in its construction including televisions. smartphones. computers, GPS units, and even wearable technology. Computers are natural applications for PCBs containing gold. and other gold elements due to the need for reliable. high-speed transfer of digital signals more suited to gold than any other metal.
 
      Gold  unrivaled in its for use in applications. that include requirements for low voltage and low resistance.  making it ideal for PCB contacts and other electronic applications. Usage of gold in manufacturing for electronic devices. has now far surpassed the consumption of the precious metal in jewelry fabrication.
 
      Another contribution that gold has made for technology is in the aerospace industry. With the long life expectancy and reliability of gold connections. and PCBs integrated into spacecraft. and satellites, gold is the natural choice for critical components.
 

   Measurement Apps with High-Powered Microscopes

 
  Most PCB visual inspection requires the use of microscopes by the truth. that surface-mounted components usually crammed onto little spaces.
  Danish digital microscopic lense maker Tagarno has unveiled a new app. that will allows users to execute side-by-side. comparisons of fantastic sample images to live on PCBs. or sample images of which will help speed up the inspection process.
  Tagarno says their released side-by-side app. allows users to be able to better conduct quality control checks. following component position or reflow operations. plus help users catch dropped components. or other problems in a more successful manner.
  The maker has before offered a amount of other apps to be able to more analyze proportions. verification lines. and emphasis stacking, but company someone. Sabine Svane said right now there was tremendous. demand coming from global distributors and end customers for the more abilities provided. inside the new program: “before using the app. the procedure was going to place the boards nextto the other person. and perform a  visual assessment. and evaluation of a couple of boards, ” based on Svane. “In regard some other situations, there are [none] where you have the precision. alignment characteristics. and simplicity of use in the same way as an individual do with our application. ”
  Users connect a new mouse and keyboard straight to the microscope in buy to use the app. which works with the FHD Trend, FHD Prestige plus FHD Uno models. Customers can perform a selection of functions with the comparison app. including conserve templates, add text, arrow, and circular annotations, and adjust colors.
  The auto-alignment feature in the application. allows users to more match up the reference to the sample. by making the reference trial transparent. before launching the app. the company said the merchandise had test use along with distributors. and end consumers.
As with any software, one of many qualities Tagarno shows. may be the ability to up-date features and fix pests . The business issues quarterly updates on the firmware upon its applications. to help to make sure any errors or required enhancements tackled.
  Charles King, principal expert at Pund-IT. said mt4 like other computerized optical inspection solutions. used in the high quality control method in the PCB market. but it's not clear what the unique level of differentiation is of the Tagarno application. AOI options may range from simple web-cam based inspection technological innovation. used for limited creation use to more robust commercial grade. options for high-volume processes.
 
 

    Machine Vision inside AOI

 
  Assessing 3D plus 2D images for automated optical inspection can end up. performed by machine perspective algorithms. This example from Visteon. and the Polytechnic Institute of Setúbal offers. developed for assessing 3 DIMENSIONAL solder joint inspection.
A single method to ensure equal assessment of each PCB is usually the use of certain AOI cameras. to lessen the effects of how distance from the lens affects focus. Compared to traditional cameras. AOI cameras can reduce distortion by using a telecentric contact lens. creating an orthographic discharge of a complex 3D. construction by "flattening" it to be able to two dimensions. This allows machine vision algorithms to be able to more. make correct measurements of a table.
  Another method is to capture 3D images rather. allowing algorithms to test a three-dimensional rendering of a board. Last calendar month. MEK Marantz Electronics introduced their latest system for 3D inspection of PCBs. 

 What is PCB failure? 

 
      It is important for a printed circuit board. to perform its function and support the larger electronic device. So, PCB manufacturers must have a system in place that monitors. and tests each component to ensure that it meets various standards. and delivers maximum performance.
 
      When a component fails, analysts must use various processes, tools and techniques. With accuracy, they must determine why the device failed. and how to prevent future failures. The following processes present unique challenges for electronics failure analysis:
 
Increased density
Higher lead-free process temperature requirements
Hazardous material
Recycling requirements
The need to tune PCBs to precise values
Other associated changes in PCB manufacturing
Root Cause Analysis
The fabrication of a complete PCB assembly requires. an array of machines and materials, which include:
 
Screen printers
Conveyors
Pick-and-place systems
Reflow ovens
Automated optical inspection
Solder paste
Different components
Some machines have automated features that perform checks at various points. and operators perform visual inspections before, during. or immediately after the completion of a task.
 
      Nonetheless, many PCBs will fail the final test. When a problem does occur. it is important to perform an effective electronics failure analysis to get clear. and precise details about the source of the problem.  and to ensure that it does not happen again.
 
      The technician must conduct a root cause analysis to identify the cause of the failure . not the symptoms. and take corrective action to fix the issue. Failure analysis also provides invaluable feedback to design engineers on how to:
 
      Correct minor faults that might have gone unnoticed during the initial design

     Any company that produces electronic hardware strives to achieve zero-defect production. To realize this objective.  manufacturers must have the capability. to perform some level of printed circuit board failure analysis. Some companies rely on outside expertise for more complex problems.
 
      For many high reliability systems. such as oil rigs, space satellites, implantable medical devices. and other systems failures can be devastating. In the case of consumer products, a single failure mode. which can replicate thousands or millions of times, can have a huge impact on the bottom line.
 
      Electronic device failure analysis. provides a systematic process to help organizations investigate and understand. why an electronic part failed. Depending on the nature of the failure. an effective investigation can identify the failure mode. mechanism and elements, such as stresses inducing the failure and other issues.
 
      For example, solder joint defects make up a large percentage of PCB failures. Manufacturers can discover the root cause of the defective joints. such as a lack of solder paste, a gap between the PCB pad and component lead, or poor reflow profile. and then implement preventative measures. To eliminate future failures, possible solutions may be to avoid solder paste contamination. or ensure the correct aspect ratio. The methods used in the analysis depend on the severity of the failure and the type of issue. They can range from simple electrical measurements. to the evaluation of sample cross-sections under a microscope.
 
      An effective and efficient root cause analysis ensures. that manufacturers can start the necessary corrective action to prevent. reoccurrence of the problem. Failure analysis processes test the reliability of a component product. under operation and determine how to improve the product.

What causes PCB failure?

 
     On top of rapid innovation. shrinking components and sophisticated circuit geometries. the fabrication of a printed circuit board consists of many steps and moving parts. The nature of the manufacturing process provides many opportunities. to introduce a defect in the mix, .
So, failure analysts face a variety of challenges when finding manufacturing defects:
 
      High-speed Printed Circuit Boards (HSCBs)- HSCBs. which have grown more complex and use a variety of integrated components. continue to grow in popularity. But, the components need boards that  composed of two or three materials. that increase the possibility of failure in extreme high-speed applications. Failures also occur from pins and chip placed in an incorrect manner on the board.
 
      Lead-free Assembly Process. The lead-free assembly process requires a higher temperature and traditional tin-lead solder. which leads to higher temperatures for the reflow and wave soldering. This results in an adverse effect on the solder joint and electronic components. Check out NTS Tin Whisker Testing services.
 
      Plated Through Hole Barrel Cracking- Barrel fatigue. which is the circumferential cracking of the copper plating. that forms the plated through hole (PTH wall), is the most prevalent failure mode. It occurs as a result of differential expansion between the copper plating. and the out-of-plane coefficient of thermal expansion (CTE) of the printed board.
 
      Correct Surface Finish Selection. The most important decision for the electronic assembly may be the surface furnish. which affects the process yield, the amount of rework necessary. field failure rate, the ability to test, the scrap rate and the cost.
 
      Conductive Anodic Filament Conductive Anodic Filaments (CAF) . or metallic electro migration describes an electro chemical process that. involves the transport of a metal across a nonmetallic medium . under the influence of an applied electric field. The condition causes current leakage, intermittent electrical shorts.  and dielectric breakdown between conductors in PCBs.
 
      Nonetheless, PCB manufacturers must take the proper care to adhere to exact tolerances. and specifications to avoid failures. This requires an effective root cause analysis to investigate. and probe into components and systems. and make the necessary quality improvements.


Printed circuit boards failure checking method

 

Micro-sectioning 

 
      Micro-sectioning, sometimes called Cross-sectioning or Metallographic Preparation. refers to a PCB testing method used to investigate:
 
Thermo-mechanical failures
Component defects
Opens or shorts
Processing failures due to solder reflow
Raw material evaluations
 
      The failure analyst removes a two-dimensional slice out of a sample. which uncovers features within the board. Considered a destructive testing method. micro-sectioning analysis provides the technician with a precise technique.  that isolates the relevant electronic component. and removes the part from the PCB sample.
 
       The technician puts the component into an epoxy resin. or other potting medium and leaves it to cure and solidify. After the component cures. the technician uses an abrasion technique to recede and expose the component. and polishes the part until it is reflective and ready for testing. Micro-sectioning requires the analyst to compare the sample against another functioning component. One advantage of this testing method is the ability to position the sample on a flat surface. and invest each of its parts together.
 
       Electron and optical microscopy equipment can examine plate thickness, intermittent metallic layer thickness. or failures to solder joints. The analyst must highlight the damage and identify the cause of the destruction. PC-MS-810 and ASTM E3 quality standards govern micro-sectioning tests.
 

Solderability Testing

 
      According to IPC-T-50, “base solderability” describes the ease with which a metal. or metal alloy material surface can  wetted by molten solder. under smallest realistic conditions. Often, the PCB manufacturing process can be the source of assembly problems. especially issues related to oxidation and misapplications of the solder mask. To cut the probability of failure, many manufactures test component. and PCB pad solder ability to ensure the robustness of the surface. and increase the probability of forming a reliable solder joint.
 
      The solderability failure method evaluates the strength. and quality of wetting of a solder by reproducing the contact. between the solder and the material. The wetting balance process measures the wetting force. and the time from contact to wetting force generation. Solderability testing can verify that the components will meet specifications and quality standards.
 
      The technique also helps determine what effect. if any, storage has on solder components in PCBs. It also provides an accurate measure of why a fault may have occurred. Solderability testing works for a variety of applications, including:
 
PCB coating evaluation
Solder evaluation
Flux evaluation
Benchmarking
Quality control
The failure analyst must have the experience to differentiate the various surface conditions. and understand the acceptable requirements of the testing technique. The analyst must also have the necessary expertise to  apply the specific conditions. The IPC-J-STD-002 and 003 standards govern all solderability tests.
 

PCB Contamination Testing

 
      Contamination can cause a variety of issues, including corrosion. degradation, metallization and rapid deterioration of wire bond interconnects. Although printed circuit board processing and assembly take place in an  clean environment. designed to keep the air. and components free of contamination, infection does occur . and represents one the most common causes of part failure.
 
       Human byproducts, handling, flux residues and reaction products are often sources of contamination. Many manufacturers use aggressive chemistry processes during PCB fabrication, including the following:
 
Copper etching liquid
Hot air leveling fluxes
Electrolytic solutions
Water soluble soldering
 
       The use of chemicals  requires a cleaning process. The electronic industry introduced ionic contamination testing. which measures the cleaning efficiency and stability of the cleaning process. Contamination testing measures the amount of ionic contamination contained in a sample. The process of testing for contamination involves the. immersion of the PCB sample into a solution. The solution dissolves the ionic contamination, which causes a change. in the constitution of the solution. and has a significant influence on the values or readings.
 
      The technician measures the change in the resistance of the solution solvent. a change in resistance that a failure analyst can measure. Then, the analyst plots the contamination level on a contamination-testing curve. and compares the value with industry standards.
 
      When a reading exceeds an established level. it confirms that the manufacturer has a problem with the cleaning process. This can cause detrimental effects, including corrosion. and electrochemical migration, when parts remain in the component. This dissolving technique can detect even the smallest parts.
 
      One of the advantages of contamination analysis is its precision and accuracy. Contamination analysis must meet the standards of IPC-TM-650, method 2-3-25 for iconic cleanliness.
 

Optical Microscopy/SEM

 
      Optical microscopy may be one of the most popular. and preferred testing methods used for detecting faults, defects. and problems associated with soldering and assembly. Many customers choose optical microscopy because of its speed and accuracy. The process uses a high power microscope with visible light. The microscope, which can reach up to 1000X, has a small depth field and shows features in a single plane. Board integrity represents a major concern and frequent cause of failure in electronics. Microscopy testing can verify improper construction. which can lead to stresses that can expose flaws at certain cross sections.
 
      Sometimes PCB failure analysis requires more powerful magnification tools. Scanning electron microscopes. or SEMs offer a highly-effective testing technique for performing semiconductor die failure analysis. Even if a defect on an integrated circuit measures only a few nanometers wide. SEM provides the failure analyst detailed images at higher magnifications. up to 120,000X. It is typical to have magnifications of 50,000 to 100,000X, and feature resolutions down to 25 angstroms. The analyst produces a recording and record of the findings based on the images.
 
      With SEM technology, the depth of the field. provides failure analysts a three-dimensional view of the sample. SEM examinations can verify semiconductor die metallization, integrity and quality. SEM also provides evidence of heat treatment and identifies the metal or alloy used. Many analysts pair SEM with micro-sectioning testing.
 

 X-ray Inspection
 

      Many X-rays provide users a powerful tool for non-invasive failure analysis. With a choice of basic film X-ray, real time X-ray and 3-dimensional X-ray systems. users can use the tools to detect actual or potential defects. They can also inspect a component that has hidden joints or parts located underneath a chip. The analyst uses an X-ray inspection instead of visible light equipment to test  the PCB.
 
       Even with basic X-ray inspection capabilities. technicians can conduct the following types of internal component examinations:
 
Internal particles
Internal wire dress
Die attach quality
Voids in the sealing lid
Substrate /printing wiring board trace integrity
Insufficient excessive or poor solder
 
      The advantage of this testing method is the ability to detect surface . and internal flaws in a non-destructive manner. while keeping samples in pre-testing condition.

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