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Flex PCB Blog
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What is FPC
Special attention points for flexible circuit wiring
Multilayer PCB Stack-up Basics | PCB Knowledge
PCB Protection: Potting or Conformal Coating? | PCB Knowledge
FPCway: Specialized manufacturer of flexible printed circuit boards and rigid-flexible printed circuits
Future Trends of Flexible Circuit Boards
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Control Impedance Between Rigid PCB and Flex PCB
Flex PCB Reliability and Bendability
Normal Flex PCB Specifications
Flex PCB Polyimide Coverlay and Solder Mask
Flex PCB Boards and Connectors
About RA Copper and ED Copper
Introduction of Flexible PCB
5 Tips For Designing Flexible PCB
Advantages of FPC (Flexible PCB)
Evolution of the Flex Printed Circuit Board
Benefits of Using Flex Circuit Boards
Why Rigid-Flex PCBs are Economical?
Flexible PCB vs Rigid PCB
Development of Flexible printed circuit board (FPC) market
Traditional Manufacture Engineering of FPC Substrate
Development Trend of FPC Board
Flex PCB and the Manufacturing
About Flex PCB design
About Flex PCB and Assembly
How to Ensure Flex PCB Design Success
How to Select the Appropriate FPC Materials?
The Differences In Rigid PCB, Flex PCB and Rigid-Flex PCB
Flex-Rigid PCB Design Guidelines
Beneficials for Polyimide Flex PCB Boards
About Stiffener on Flex PCB FPC circuit Boards
PCB Surface Finish Comparison
Copper Thickness for FPC Boards
Interconnect Solutions for Flexible Printed Circuits and Etched Foil Heaters
Advantages and Disadvantages of Rigid-Flex PCB
About FPC Plating Process
About EMI shield design for Flex Printed Circuit Board
PCB Assembly Blog
How to solve the problem of PCB warping deformation after welding large copper bar?
About PCB Assembly
QFP and BGA and the Development Trend in PCB assembly
Why some components need be baked before reflow soldering
About Flex PCB Assembly
Manual Soldering in SMT Assembly Manufacturing Process
BGA Components and BGA Assembly
Quick Understanding for PCB Assembly Process
About SMT Assembly (Surface Mount Technology)
About THT Assembly (Through-Hole Technology)
About Reflow Soldering
PCB Assembly Inspections and Tests
Panel Requirements for PCB Assembly
About SMT (Surface Mount Technology)
FPC Research Blog
Preparation of FPC based on ultrasonic spraying method_4_Experimental Results
Preparation of FPC based on ultrasonic spraying method_3_Experimental Procedure
Preparation of FPC based on ultrasonic spraying method_2_Experimental Platform and Principle
Preparation of FPC based on ultrasonic spraying method_1_abstract
Research on Layout Design Method of Ultra-thin FPC_4_Analysis of Layout Design Methods
Research on Layout Design Method of Ultra-thin FPC_3_Analysis of Layout Design Methods
Research on Layout Design Method of Ultra-thin FPC_2_Analysis of Layout Design Methods
Research on Layout Design Method of Ultra-thin FPC_1_introduction
Research progress on polyimide FPC_2_the field of FPC
Research progress on polyimide FPC_1_Introduction
Analysis of Vibration Characteristics of FPCBs _4_Summary
Analysis of Vibration Characteristics of FPCBs _3_Finite Element Analysis
Analysis of Vibration Characteristics of FPCBs _2_Theory of Vibration Analysis
Analysis of Vibration Characteristics of FPCBs Under Random Vibration_1_Introduction
Design Methods for FPCBs_5_Practical Application
Design Methods for FPCBs_4_Electrical Circuit Design and Examples
Design Methods for FPCBs_3_Structure Design Method and Examples
Design Methods for FPCBs_2_Component Selection Methodology and Examples.
Research on Design Methods for FPCBs
Application of MPW technique for FPCBs _4_Summary
Application of MPW technique for FPCBs_3_Experimental results
Application of MPW technique for FPCBs_2_Experimental setup
Application of MPW technique for FPCBs_1_Principle of MPW
Application of FPCB in PC motherboards_4_ Results and discussion
Application of FPCB in PC motherboards_3_ Numerical analysis
Application of FPCB in PC_2_ Experimentation
Application of FPCB in PC motherboards
A Bus Planning Algorithm for FPC Design _4_Experimental result
A Bus Planning Algorithm for FPC Design _3_Proposed Algorithm
A Bus Planning Algorithm for FPC Design _2_Preliminaries
A Bus Planning Algorithm for FPC Design _1_Introduction

Responsible Printed Circuit Board (PCB) manufacturers all inspect boards on different positions in the process of assembly in order to eliminate appearance defects and find out numerous assembly errors prior to electric testing and collect data for statistical process. The inspection of PCBA boards always include: Visual inspection, AOI, X-Ray, FCT Test, ICT Test, etc. The crucial step for this goal lies in the implementation of rigorous quality administration system. Progress and wider application of SMT (Surface Mount Technology) brings about higher requirement for inspection because solder joints applying SMT have to withstand more stress than those applying via plating technology. Component leads with the application of SMT have to withstand more structural load, so SMT solder joints can't be firmly soldered on board unless a large amount of solder is applied. As a result, long-term electric reliability of PCBs loading with SMT components greatly depends on structural integrity of solder joints.

Inspection Technology


Up to now, apart from ordinary visual inspection, multiple procedure testing technologies are applied with different prices, performances and fault coverage. Automated testing technologies include optical inspection, laser triangle inspection, X-ray inspection and X-ray layering technology. In order to implement optimal procedure testing, PCB manufacturers should be aware of pros and cons of each type of testing technology and what each method is good at. All these technologies can be classified into two categories at the highest rank: visual inspection and automated procedure testing system.


Visual inspection


Visual inspection can be implemented after implementations of lots of steps in the process of PCBA. However, equipment selection applied in visual inspection lies in positions that need to be inspected. For example, after solder paste printing and component placement, inspectors can effectively inspect large defects just with their eyes. They are capable of inspecting contaminated solder paste and missing components in less than one minute and micrometer ocular and difference Z high-degree detector can be applied for sampling inspection to inspect quality of solder paste deposition. Focusing on edge of copper pad, Z high-degree detector is adjusted to zero and then focus is set to be at the top surface of solder paste deposition so that height of solder paste deposition can be measured. The most popular visual inspection is capable of accurately inspecting reflow solder joints through observing light ray of solder joint surface reflected by ordinary prism from different perspectives.


According to the size of solder joints, required amplification coefficient ranges from four-time center distance (≥1.25mm) to fifteen-time fine pitch (≤0.5mm). This inspection method is carried out based on established visual quality standard such as Mil-Std-2000A and ANSI/J-Std-001 to compare attributes of solder joints. Generally speaking, with this method applied, five solder joints can be inspected each second. Validity of visual inspection depends on inspectors' capability, consistency of standards followed and applicability of quality of visual inspection. Inspectors must master technological requirement of each type of solder joint because each type of solder joint possibly carries 8 kinds of different fault standards and each type of PCB features more than 6 kinds of solder joints according to different component assembly.


As a result, visual inspection is impractical for quantitative measurement to support effective procedure control. Moreover, this method doesn't work on hidden solder joints inspection such as J lead components with high-density package, extra-fine square flat pack, surface array flip chip and solder joints on BGA. Through common and clear rules establishment, visual inspection is capable of providing technology that is easily implemented and this type of technology works really well on procedure development evaluation and large surface defect inspection.


Automated Optical Inspection (AOI) system


Applying multiple light sources, programmable LED library and multiple cameras, AOI system picks up images of solder joints through its irradiation from different perspectives. Leads and solder joints are like reflecting mirror in reflecting light while PCB and SMT components reflect little light. Reflecting light from solder joints fails to provide practical height data. However, image and intensity of reflecting light provide information on curvature of solder joints whose analysis can be applied to determine whether solder joints are complete or not and solder sufficient or wetting disqualified. Furthermore, AOI system is also capable of effectively inspecting solder bridge and loss or skew of components before or after soldering.


Inspection rate of these systems is 30 to 50 joints per second and they feature a relatively low price that is 150 thousand to 250 thousand dollars per device. Nonetheless, AOI system fails to inspect parameters of some solder joints such as height of solder joint behind leads, solder amount within a joint, which makes capability of structure procedure control prohibited. Moreover, these systems fail to inspect hidden solder joints such as solder joints of BGA, PGA and J-type lead components that, however, are quite crucial to soldering reliability. AOI system does best in inspecting chips and gull wing shaped components whose pitch is more than 0.5mm.


X-ray perspective system


X-ray perspective system transmits a beam of radiation from a point light and vertically through PCB. With radiation passing through PCB, solder joints make radiation intensity weakened by a much higher extent than that caused by other materials on the board. These intensity changes on radiation energy are transformed into digital X-ray image at a 256 grey scale. An X-ray image at grey scale of a solder joint is as a matter of fact a density diagram indicating solder joint thickness, distribution and internal integrity. On single-sided PCB, X-ray perspective system is capable of accurately inspecting defects of solder joints such as those on J-type lead components, gull wing-shaped components, passive chips and transistors with a small scale. These systems also can inspect escaped components and inverted tantalum capacitor. When it comes to double-sided boards, X-ray perspective image of solder joints may be overlapped with that of solder joints at the bottom, which makes it difficult for accurate measurement.


FCT Test


FCT Test refers to functional testing. Typically, the functional test is performed during the last phase of the production line.[1] This is often referred to as a final quality control test, which is done to ensure that specifications are carried out by FCTs. The process of FCTs is entailed by the emulation or simulation of the environment in which a product is expected to operate. This is done so to check, and correct any issues with functionality. The environment involved with FCTs consists of any device that communicates with an DUT, the power supply of said DUT, and any loads needed to make the DUT function correctly. FCTs uses customer specific connectors, rather than a test point on the PCB. Functional tests are performed in an automatic fashion by production line operators using test software. In order for this to be completed, the software will communicate with any external programmable instruments such as I/O boards, digital multimeters, and communication ports. In conjunction with the test fixture, the software that interfaces with the DUT is what makes it possible for a FCT to be performed


ICT Test

ICT Test refers to In-Circuit Test. ICT is a powerful tool for printed circuit board test. Using a bed of nails in-circuit test equipment it is possible gain access to the circuit nodes on a board and measure the performance of the components regardless of the other components connected to them. Parameters such as resistance, capacitance and so forth are all measured along with the operation of analogue components such as operational amplifiers. Some functionality of digital circuits can also be measured, although their complexity usually makes a full check uneconomic. In this way, using ICT, In-Circuit Test, it is possible to undertake a very comprehensive form of printed circuit board test, ensuring that the circuit has been manufactured correctly and has a very high chance of performing to its specification.


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