Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
IPC-4921: Substrate Classification, Testing & Specification Sheets for Printed Electronics
Selecting the right substrate for printed electronics is half the battle. You can have the best silver nanoparticle ink on the market, but if your PET film can’t handle the sintering temperature or your polyimide warps during processing, the entire project fails. IPC-4921 provides the standardized framework for specifying, qualifying, and procuring printed electronics substrates that actually work with your materials and processes.
After years of dealing with substrate-related failures in printed electronics production, I’ve come to appreciate how IPC-4921 eliminates the guesswork from material selection. This guide breaks down everything engineers need to know about the standard, from classification systems to specification sheets.
What is IPC-4921?
IPC-4921, officially titled “Requirements for Printed Electronics Base Materials (Substrates),” establishes the classification system, qualification requirements, and quality conformance specifications for substrate materials used in printed electronics applications. Developed jointly by IPC and the Japan Electronics Packaging and Circuits Association (JPCA), this standard provides comprehensive data for selecting compatible base dielectric materials.
Document Attribute
IPC-4921 Details
Full Title
Requirements for Printed Electronics Base Materials (Substrates)
Joint Development
IPC and JPCA
Current Revision
IPC-4921A (2017)
Original Release
2012
Specification Sheets
6 material types included
Developed By
Printed Electronics Base Material/Substrates Subcommittee (D-62)
The standard defines base material only and should not be used for substrates that have been post-processed and comprise defined features or structures such as conductive traces. Once you print on a substrate, it becomes a printed electronics assembly covered by other standards.
Why Substrate Selection Matters in Printed Electronics
Unlike traditional PCB fabrication where FR-4 dominates, printed electronics uses diverse substrate materials ranging from commodity PET films to specialty polyimides and even paper. Each substrate brings different thermal limitations, surface characteristics, and mechanical properties that directly impact print quality and product reliability.
Critical Substrate Considerations
Thermal Compatibility: Your substrate must survive the ink curing process. Silver nanoparticle inks typically require 120-300°C sintering temperatures. A PET substrate with a 150°C limit cannot be used with inks requiring 200°C curing.
Surface Energy: Ink wetting and adhesion depend heavily on substrate surface energy. Untreated polymer films often require corona or plasma treatment to achieve acceptable ink adhesion.
Dimensional Stability: Substrates that shrink, expand, or warp during processing cause registration errors in multi-layer printed electronics. This becomes critical for fine-pitch features.
Roll-to-Roll Compatibility: High-volume printed electronics manufacturing uses roll-to-roll processes. Substrates must maintain web handling characteristics throughout printing, curing, and converting operations.
IPC-4921 Classification System Explained
One of IPC-4921’s most valuable features is its systematic classification approach. The standard provides a structured method for designating substrate materials on master drawings and procurement documents.
For example, IPC-4921/2 refers to the specification sheet detailing Polyester Naphthalate (PEN) / Biaxially Oriented Polyethylene Naphthalate (BOPEN).
Classification by Base Material Type
Material Type Code
Material Description
Common Trade Names
PET
Polyethylene Terephthalate
Mylar, Melinex
PEN
Polyethylene Naphthalate
Teonex, Kaladex
PI
Polyimide
Kapton, Upilex
Paper
Cellulose-based substrates
Various
Glass
Thin flexible glass
Willow Glass
PC
Polycarbonate
Lexan, Makrolon
Classification by Base Structure
Structure Code
Description
Characteristics
BO
Biaxially Oriented
Balanced properties in both directions
UO
Uniaxially Oriented
Enhanced properties in one direction
Cast
Cast film
Isotropic properties
Coated
Surface-treated
Enhanced adhesion or barrier
Classification by Thickness
Designers can specify substrate thickness as part of the material designation. Common thicknesses range from 12 µm to 250 µm depending on application requirements.
Thickness Range
Typical Applications
12-25 µm
Ultra-thin flexible electronics
25-50 µm
Standard flex circuits, sensors
50-125 µm
Robust flexible electronics
125-250 µm
Semi-rigid applications
Substrate Materials Covered in IPC-4921
IPC-4921 includes specification sheets for the major substrate materials used in printed electronics. Understanding each material’s properties helps engineers make informed selections.
PET (Polyethylene Terephthalate) Substrates
PET is the workhorse of printed electronics substrates due to its low cost, good clarity, and adequate performance for many applications.
Property
Typical PET Value
Notes
Glass Transition (Tg)
78-80°C
Limits processing temperature
Max Processing Temp
120-150°C
Depends on stabilization
Tensile Strength
170-200 MPa
Good mechanical strength
Moisture Absorption
0.4-0.5%
Moderate
Dielectric Constant
3.0-3.2
At 1 MHz
Optical Clarity
Excellent
>90% transmission
Relative Cost
Low
Most economical option
Best Applications: Consumer electronics, RFID tags, touch sensors, smart packaging, disposable medical devices.
Limitations: Cannot withstand SMT reflow temperatures; limited to low-temperature curing inks; may deform under thermal stress.
PEN (Polyethylene Naphthalate) Substrates
PEN fills the performance gap between PET and polyimide, offering improved thermal and mechanical properties at moderate cost.
Property
Typical PEN Value
Comparison to PET
Glass Transition (Tg)
120-125°C
+40°C higher
Max Processing Temp
180-200°C
+50°C higher
Tensile Strength
250-280 MPa
40% stronger
Moisture Absorption
0.2-0.3%
50% lower
Dielectric Constant
2.9-3.1
Slightly lower
Dimensional Stability
Excellent
Better than PET
Relative Cost
Moderate
2-3x PET cost
Best Applications: Automotive electronics, industrial sensors, displays, applications requiring better thermal stability than PET.
Advantages Over PET: Higher processing temperature allows wider ink selection; better dimensional stability improves registration; lower moisture absorption enhances reliability.
Polyimide (PI) Substrates
Polyimide represents the gold standard for high-performance flexible electronics substrates, offering exceptional thermal and chemical resistance.
Property
Typical PI Value
Notes
Glass Transition (Tg)
360-410°C
Exceptionally high
Max Processing Temp
300-400°C
Enables all curing methods
Tensile Strength
230-350 MPa
Excellent
Moisture Absorption
2.0-3.0%
Higher than PET/PEN
Dielectric Constant
3.4-3.5
At 1 MHz
Chemical Resistance
Excellent
Withstands harsh solvents
Relative Cost
High
5-10x PET cost
Best Applications: Aerospace, medical implants, automotive under-hood, military electronics, any application requiring high-temperature processing or operation.
Trade-offs: Higher moisture absorption requires careful handling; significantly higher cost limits use in cost-sensitive applications; amber color eliminates transparent applications.
Paper Substrates
Paper substrates enable ultra-low-cost printed electronics for disposable and sustainable applications.
Property
Typical Paper Value
Notes
Max Processing Temp
150-200°C
Depends on treatment
Tensile Strength
20-80 MPa
Much lower than polymers
Moisture Sensitivity
High
Requires protection
Surface Roughness
1-10 µm Ra
Rougher than films
Biodegradability
Yes
Environmental benefit
Relative Cost
Very Low
Lowest cost option
Best Applications: Smart packaging, disposable sensors, environmental monitoring, educational kits, single-use medical diagnostics.
Thin flexible glass combines the superior surface quality of glass with enough flexibility for roll-to-roll processing.
Property
Typical Thin Glass Value
Notes
Max Processing Temp
600°C+
Highest of all substrates
Surface Roughness
<1 nm Ra
Atomically smooth
Moisture Barrier
Excellent
Near-hermetic
Dielectric Constant
5-7
Higher than polymers
Flexibility
Limited
Bend radius >20mm typical
Relative Cost
Very High
Premium material
Best Applications: High-performance displays, precision sensors, applications requiring hermetic barriers or high-temperature processing.
Key Substrate Properties in IPC-4921
IPC-4921 specification sheets document critical properties that designers need for material selection.
Thermal Properties
Property
Test Method
Why It Matters
Glass Transition (Tg)
DSC
Maximum safe processing temp
Melting Point (Tm)
DSC
Absolute temperature limit
Coefficient of Thermal Expansion
TMA
Dimensional stability
Thermal Conductivity
Laser flash
Heat dissipation
Heat Shrinkage
Oven test
Post-processing dimensions
Mechanical Properties
Property
Test Method
Why It Matters
Tensile Strength
ASTM D882
Handling and durability
Elongation at Break
ASTM D882
Flexibility
Tear Resistance
Elmendorf
Processing durability
Flex Endurance
IPC-TM-650
Dynamic flex life
Surface Roughness
Profilometry
Print quality
Electrical Properties
Property
Test Method
Why It Matters
Dielectric Constant (Dk)
IPC-TM-650
High-frequency performance
Dissipation Factor (Df)
IPC-TM-650
Signal loss
Volume Resistivity
ASTM D257
Insulation quality
Surface Resistivity
ASTM D257
ESD performance
Dielectric Strength
ASTM D149
Voltage withstand
Dimensional Properties
Property
Test Method
Why It Matters
Thickness Tolerance
Micrometer
Layer-to-layer consistency
Moisture Absorption
ASTM D570
Dimensional stability
Humidity Expansion
TMA
Environmental stability
Shrinkage (MD/TD)
IPC-TM-650
Registration accuracy
IPC-4921 Specification Sheets Explained
IPC-4921 includes six materials specification sheets that provide standardized property data for common substrate types. Each specification sheet follows a consistent format enabling direct material comparison.
Specification Sheet Structure
Each IPC-4921 specification sheet includes:
Material Identification: Official designation and common names
Scope: Intended applications and limitations
Classification: Material type, structure, and variants
Requirements: Minimum property values
Quality Assurance: Testing and certification requirements
Packaging: Handling and storage requirements
Using Specification Sheets for Procurement
When specifying substrates in procurement documents, reference the IPC-4921 specification sheet number:
Specification Sheet
Material
Example Designation
IPC-4921/1
PET
IPC-4921/1, 50µm
IPC-4921/2
PEN (BOPEN)
IPC-4921/2, 75µm
IPC-4921/3
Polyimide
IPC-4921/3, 25µm
IPC-4921/4
Paper
IPC-4921/4, coated
IPC-4921/5
Glass
IPC-4921/5, 100µm
IPC-4921/6
Specialty
Per application
This designation system ensures suppliers understand exactly what material is required, eliminating confusion from marketing names or generic descriptions.
What is the difference between IPC-4921 and IPC-4591?
IPC-4921 covers base materials (substrates) — the films or sheets you print electronics onto. IPC-4591 covers functional conductive materials (inks and pastes) — what you actually print. Think of IPC-4921 as specifying the paper in a printing operation, while IPC-4591 specifies the ink. Both standards use similar classification and qualification frameworks and are designed to work together for complete printed electronics material specification.
How do I designate a substrate material using IPC-4921?
Use the format: IPC-4921/[specification sheet number], followed by any additional details. For example, “IPC-4921/2, 75µm, heat-stabilized” designates a 75 µm thick, heat-stabilized PEN substrate per specification sheet 2. Include this designation on master drawings and procurement documents to ensure suppliers understand exactly what material you require.
Can I use IPC-4921 for traditional flex PCB substrates?
IPC-4921 is specifically designed for printed electronics substrates, not traditional copper-clad flex circuit materials. Traditional flex PCB base materials are covered by IPC-4202 (Flexible Base Dielectrics) and IPC-4203 (Adhesive Coated Dielectric Films). However, there is overlap in materials like polyimide, and the property requirements are similar.
What if my substrate isn’t covered by an existing IPC-4921 specification sheet?
If you’re using a material not covered by the six existing specification sheets, IPC-4921 section 1.2.2.2 provides guidance for specifying materials by type rather than specification sheet. You can also work with IPC to submit new specification sheets for inclusion in future standard revisions. Many emerging substrates like stretchable polymers and bio-based films are candidates for future specification sheets.
How does substrate selection affect printed electronics reliability?
Substrate selection directly impacts reliability in several ways. Thermal mismatch between substrate and printed conductors causes stress during temperature cycling, leading to cracking or delamination. Moisture absorption causes dimensional changes that stress printed features. Surface contamination or inadequate surface energy leads to adhesion failures. IPC-4921 specification sheets provide the property data needed to evaluate these reliability factors during material selection.
Implementing IPC-4921 in Your Organization
Successfully implementing IPC-4921 requires coordination across design, procurement, and manufacturing functions.
Design Engineering Implementation
Specify substrate materials using IPC-4921 designations on drawings
Reference specification sheet properties in design calculations
Verify ink-substrate compatibility before finalizing designs
Document substrate selection rationale in design files
Procurement Implementation
Include IPC-4921 compliance in substrate supplier qualifications
Request IPC-4921 specification sheet data from all suppliers
Establish incoming inspection procedures per IPC-4921 testing
Maintain approved substrate list with IPC-4921 classifications
Manufacturing Implementation
Verify substrate properties during incoming inspection
Monitor storage conditions per IPC-4921 requirements
Track lot traceability for substrate materials
Document any substrate-related process deviations
Conclusion
IPC-4921 provides the essential framework for specifying, qualifying, and procuring substrate materials for printed electronics. The standard’s classification system, specification sheets, and testing requirements transform substrate selection from an ad-hoc process into a systematic, documented approach that ensures material consistency and compatibility.
Whether you’re printing silver sensors on PET film, high-temperature circuits on polyimide, or disposable electronics on paper, IPC-4921 provides the common language and technical requirements that connect substrate suppliers with printed electronics manufacturers. Combined with IPC-4591 for conductive materials and IPC-2292 for design requirements, IPC-4921 forms a cornerstone of the printed electronics standards ecosystem.
For engineers working in printed electronics, understanding IPC-4921 is not optional — it’s fundamental to successful material selection and product reliability. The time invested in learning the standard pays dividends through reduced material qualification cycles, fewer production issues, and more reliable products.
Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
