Introduction
Ordering custom printed circuit boards (PCBs) involves procuring fabrication and assembly services spanning many details from the bare boards themselves to populated assemblies. With various sourcing options, specifications, and stages in the process, knowing how to effectively order PCBs helps streamline procurement and avoid missteps. This guide covers PCB ordering considerations including prototyping vs production, sourcing options, required files, specifications, procurement process, quality assurance, assembly, testing, and more to aid your PCB sourcing.
Prototyping vs Production
The first consideration is whether this is a prototype build or full production run.
Prototyping
- Lower volumes like 1-10 units
- Faster lead times
- More flexibility in specifications
- Verifying design before full production
- Chance to test manufacturability before committing
Production
- Bulk order of often hundreds or thousands of boards
- Longer lead times
- Tighter tolerances and requirements
- Optimization for mass manufacturing
- Lower per unit costs at volume
- Long term supply arrangements
PCB Fabrication Sources
There are several options when sourcing bare PCB fabrication:
Domestic Fabricators
- Located in the same country you operate (e.g. U.S.)
- Provides local engineering support
- Easier logistics and supply monitoring
- Required for defense/government projects
- Typically costlier for mid to high volume
Asian Fabricators
- Located in China, Taiwan, etc.
- Lower cost due to labor, overhead, automation
- Capable of very high volume production
- Language and time zone barriers
- Difficult to monitor and visit facilities
Online Sourcing Platforms
- Instant access to quotations
- Broad range of fabricator capabilities and locations
- Aid in comparing pricing
- Less direct engineering support
- Vetting and screening burden falls on you
Choose based on capabilities required, quality, volume needs, established relationships, compliance, logistics, support needs, and other factors.
Required Ordering Information
To generate PCB fabrication quotes and orders, suppliers will need:
CAD Data
- Gerber files
- Drill files
- BOM/assembly drawings
- Layer stackup diagram
- Mechanical specifications
- Any special instructions
Material Specifications
- Board thickness
- Layer count
- Material type (FR-4, Rogers, polyimide, etc.)
- Copper thickness (1 oz, 2 oz, etc.)
- Copper finishes (HASL, immersion silver, ENIG, etc.)
- Impedance requirements
- Details on any exotic materials
Board Specifications
- Quantity required
- Panel sizes
- Hole sizes and tolerances
- Line/space widths
- Soldermask color
- Silkscreen text
- Thickness tolerances
- Electromechanical testing needs
Providing complete design data along with a detailed specifications sheet ensures you receive an accurate quotation. Always provide procurement specifcations upfront to avoid misaligned expectations.
Key Considerations
Additional factors to specify when sourcing PCB fabrication:
Special Requirements
- Material certifications (UL, IPC)
- ITAR regulations
- Qualification testing needs
- Quality management system audit rights
- Custom acceptance criteria
- Special handling requirements
Design For Manufacturing (DFM)
- Request DFM analysis on designs
- Implement DFM recommendations
- Require proof of DFM checks by fabricator
Lead Times
- Confirm standard and expedited times
- Define cancellations policy
- Expect longer times for complex boards
Revisions
- Possibility of revisions during prototyping
- Process for design change orders
Logistics
- Freight terms and use of your carrier account
- Packaging requirements
- Customs coordination
flag redYellow – highlight important points to clarify upfront based on your internal needs.
Stages of PCB Procurement
Ordering PCBs involves several milestone stages:
Quotation – Fabricators provide quotation based on specifications
Engineering Review – Opportunity to clarify specifications before order
Order Confirmation – Official PO and order placed
Fabrication – Raw board manufacturing process
Testing – Quality assurance validation per acceptance test plan
Shipment – Transfer to shipping forwarder or directly to you
Payment – According to negotiated terms like 50% deposit, 50% prior to shipment
Ongoing communication and collaboration is needed between your team and the fabricator throughout the process.
Quality Assurance
Robust quality assurance is imperative when procuring PCBs:
- Require quality certifications (ISO 9001, AS9100, etc.)
- Conduct initial audits and periodic reviews of facilities
- Review full accreditations and capabilities
- Clearly define acceptance testing criteria and requirements
- Receive electrical, dimensional, functional test reports
- Review statistical process controls and continuous improvement
- Examine defect rates and mitigations
- Validate qualification of key equipment
- Check training procedures for operators and inspectors
- Get references from existing customers on quality history
This rigorous validation reduces the risk of receiving defective boards.
Ordering PCB Assemblies
In addition to bare boards, you may require fully assembled PCBs with soldered components. This involves additional specifications:
Assembly Drawings
- Bill of materials (BOM) lists components, quantities, part numbers
- Assembly drawings show placement locations
Components
- Detail all component models, packages, part numbers
- Provide components to assembler or request procurement
Soldering Requirements
- Specify solder paste, solder composition (SnAgCu, SnPb, etc.)
- Define reflow profile requirements
- Set standards for inspection criteria (IPC-A-610)
- Request solder samples for quality validation
- Specify any selective/wave soldering steps
Functional Testing
- Define test procedures to validate assembly
- Require test reports prior to shipment
Assessment and Qualification
Evaluate assembler capabilities thoroughly:
- Quality certifications – ISO, IPC, J-STD
- Facility security and ESD controls
- SMT equipment types for accuracy, speed, precision
- AOI inspection capabilities
- Qualifications and training of operators
- Handling and storage procedures
- Experience with similar assemblies
- Existing clients as references
- Statistical process controls
- Corrective action and continuous improvement mindset
As with fabricators, intensive qualification helps reduce assembly defects.
Ordering Supporting Services
Additional services that may assist PCB procurement:
CAD Support
- Engineer team for design reviews
- DFM analysis and optimization
- Generate fabrication and assembly drawings
Component Sourcing
- Find optimal component models
- Secure sufficient stock for volumes needed
- Qualify and manage multiple vendors
Logistics
- Shipping and freight forwarding
- Customs brokerage
- Handling, tracking, insurance
Look for providers offering the breadth of services surrounding fabrication/assembly to streamline the full procurement process.
Conclusion
Ordering PCBs spans conceptualization through delivery – involving planning, design data, specifications,Revision – suggestions procurement, fabrication, test, shipments, and quality assurance. Careful attention to details like qualification, acceptance criteria, DFM, and change control reduces delays and costly defects. Leveraging the expertise of fabricators, assemblers, and procurement specialists optimizes the process. Establishing mutual understanding and collaboration early allows projects to meet cost, schedule, and performance objectives. With the myriad details involved in procuring boards and assemblies, having a solid ordering process lays the groundwork for project success.
Frequently Asked Questions
Q: What are some typical lead times for PCB fabrication?
Typical lead times range from 2 days for expedited prototyping to 3 weeks for higher layer count standard delivery. However, maximum lead times can reach 10 weeks or more for highly complex PCBs requiring iterative engineering review.
Q: Should PCB designers talk directly with fabricators?
Direct engineering collaboration between designers and fabricators helps assess manufacturability upfront in the design stage and through prototyping. This prevents issues later on. Designers should partner closely with their fabricators.
Q: What data should be requested from PCB fabricators as deliverables?
Typical deliverables include electrical test reports, dimensional measurements, visual quality reports, material certs, impedance reports, coupon cross-section data, and any other contractually defined verification.
Q: How are PCB panels utilized differently for prototyping vs production?
In prototyping, panel sizes are maximized to reduce cost even if quantities are low. In full production, panel sizes are optimized to maximize manufacturing efficiency and yield.
Q: Why is component sourcing important when ordering assemblies?
Insufficient qualified component stock when assembling finished boards can cause major delays or shortages. Strategic component sourcing as part of assembly procurement reduces this risk.
