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Because we make no compromises on our incoming quality assurance, we refuse to compromise on our outgoing quality. Our professional team maintain constant vigilance over our processes, we know that our products are created with the best possible processes, and that everything we do conforms to the ISO bodies to which we subscribe.We invite you to rely on our service. We value the faith and trust of our customers above everything, and do everything possible to ensure that your expectations are met or exceeded. We have a proven track record of quality that we intend to maintain.
Printed circuit boards (PCBs) are complex products that require extensive quality control throughout the fabrication process. Final quality control (FQC) conducted at the end of manufacturing is critical for verifying boards meet all specifications prior to shipment. This article provides an overview of FQC processes in PCB production, including:
- Importance of FQC inspection
- Typical FQC tests and criteria
- Automated optical inspection (AOI)
- Cleanliness testing
- Electrical testing
- Quality documentation
- Implementing effective FQC
Proper final quality control gives confidence that only conforming, reliable PCBs are released to customers.
The Importance of FQC Inspection
FQC provides the last opportunity for PCB manufacturers to thoroughly inspect boards coming off the production line. The goals of final quality control include:
- Validate quality – Verify all acceptance criteria and customer requirements are fully met.
- Detect defects – Identify any residual defects that escaped earlier processes.
- Ensure reliability – Confirm proper fabrication to deliver robust, reliable PCBs.
- Reduce field failures – Prevent defective boards from reaching customers where issues become more costly.
- Control risk – Avoid potential liabilities from out-of-spec boards reaching end-products.
Robust FQC programs are essential for protecting manufacturers’ reputations and customers’ interests by screening out defective boards before they leave the factory.
Typical FQC Inspection Criteria
While criteria vary by product type and customer, common quality checks in FQC inspection include:
Visual Attributes – Board dimensions, conductor spacing/widths, layer-to-layer registration, land/hole integrity, plating flaws, handling damage, etc.
Solder Mask Quality – Coverage, expansions, voids, scratches, discoloration, residue
Legend Print – Legibility, smearing, misregistration, spacing
Cleanliness – No residual contamination from processes
Plating Integrity – Proper plating of edge contacts, holes, vias
Electrical Tests – Continuity, isolation, netlist verification, functional test
Packaging – Proper quantity, marking, ESD protection
Combining thorough visual, mechanical, electrical, and cleanliness testing ensures boards are free of defects and meet all specifications.
Automated Optical Inspection (AOI)
Automated optical inspection (AOI) is a key technique used during final quality control to supplement manual inspection:
- High-speed 2D and 3D machine vision scanning of 100% of PCBs
- Detects micro-level defects difficult to see manually
- Inspects solder mask, legend, component pads, spacing, traces, holes, etc.
- Can perform automated optical measurement
- Creates pass/fail map of board with images of any defects found
- Reduces reliance on operator inspection skills
- Improves consistency and reduces human errors
AOI greatly enhances the inspection coverage, accuracy, repeatability, and efficiency of final PCB inspections.
Verifying boards meet cleanliness specifications is another key focus of FQC:
|Test Method||Contaminants Detected|
|Ion Chromatography||Ionic contamination like chlorides, sulfates|
|Atomic Absorption Spectroscopy||Metallic elements, residues|
|Combustion-Infrared||Total organic carbon levels|
|Visual Inspection||Visible particles, fibers, stains|
Ensuring PCBs meet stringent cleanliness standards prevents issues like electrochemical migration and allows safe, reliable electronics assembly.
Various electrical tests are deployed during final quality control:
- In-circuit Testing – Validates proper connections between components
- Flying Probe – Checks shorts, opens, and proper nets/nodes
- Boundary Scan – Tests interconnectivity of components with embedded logic
- Built-in Self Test – Executes functionality checks based on circuit design
This validates the board functions electrically according to its design. Catching hard defects improves test yields for customers.
Detailed quality records are maintained covering the FQC process:
- Inspection reports itemizing checks performed and results
- AOI defect images with board mapping
- Electrical test data logs
- Re-inspection records after rework
- Certificates of conformance
These quality documents prove the PCBs shipped conform fully to specifications and provide traceability.
Implementing Effective FQC
Maximizing the value of final quality control requires:
- Clear inspection criteria – Unambiguous, quantifiable acceptance standards
- Representative sampling – Statistically valid sample sizes
- Standard procedures – Consistent, documented processes
- Operator training – Ensuring competency in inspection methods
- Traceability – Linking results to individual PCBs and lots
- Corrective action – Addressing root causes of failures to prevent recurrence
- Continuous improvement – Using quality data to refine and enhance FQC over time
With rigorous quality control testing implemented at the end of manufacturing, PCB fabricators can confidently release only conforming boards to customers and prevent functional issues arising in the field.
Frequently Asked Questions
How is final quality control different than inspection during fabrication?
FQC provides end-of-line testing to catch any defects that escaped in-process inspection. It also validates 100% conformance to all specifications prior to shipment.
What are the main limitations of manual visual inspection?
Human inspectors can miss micro-level defects, have variable skill, get fatigued, and suffer from inattentional blindness over time. Automated inspection improves consistency.
How can I request specific FQC criteria for my PCB order?
Communicate upfront any special FQC needs or acceptance criteria above standard procedures. These can be listed on fabrication drawings or purchase orders for the PCB supplier to follow.
Should every board be functionally tested, or is sampling acceptable?
For medium-large batches, a statistical sample plan with acceptance quality levels can provide confidence without 100% functional testing. Work with your PCB supplier to determine an optimal approach.
What FQC documentation should I expect from my PCB manufacturer?
Typical documents are inspection reports, AOIs, electrical test reports, certificates of conformance, and failure analysis reports. Ensure you can trace results to individual board serial numbers.