Within Kingboard's extensive KB-6165 family, two variants address specialized requirements that the standard KB-6165 and KB-6165F cannot: KB-6165C provides halogen-free compliance for markets and OEMs requiring elimination of brominated flame retardants, while KB-6165LE delivers the absolute lowest Z-axis expansion available at the mid-Tg performance level. Neither is a general-purpose material. Both exist because specific customer requirements, regulatory mandates, or extreme reliability targets demand capabilities beyond the standard mid-Tg offering.
Understanding when these variants are necessary—and when the standard KB-6165 or KB-6165G alternatives are more appropriate—is the purpose of this guide.
In This Guide
- The KB-6165 Family: Seven Variants and How They Relate
- KB-6165C Specifications and Halogen-Free Compliance Details
- KB-6165LE Specifications and Ultra-Low Expansion Performance
- When Halogen-Free Compliance Is Actually Required
- When Ultra-Low Expansion Justifies the Premium
- KB-6165C vs KB-6165G vs KB-6165GC: Halogen-Free Comparison
- KB-6165LE vs KB-6168LE: Mid-Tg vs High-Tg Low Expansion
- Manufacturing Considerations for Specialty Variants
- Applications and Industry Segments
- Request a Quote from APTPCB
The KB-6165 Family: Seven Variants and How They Relate
KB-6165 spans the most extensive variant family in Kingboard's portfolio. Each variant modifies the base mid-Tg phenolic-cured platform for a specific property combination:
| Variant | Tg | Key Feature | Filled | Halogen-Free | Anti-CAF |
|---|---|---|---|---|---|
| KB-6165 ✓ | 153°C | Base unfilled mid-Tg | No | No | Yes |
| KB-6165F ✓ | 157°C | Filled for lower CTE | Yes | No | Yes |
| KB-6165C | ~150°C | Halogen-free (non-G series) | No | Yes | Yes |
| KB-6165LE | ~155°C | Ultra-low Z-axis expansion | Yes | No | Yes |
| KB-6165G ✓ | 155°C | Halogen-free (G series) | Yes | Yes | Yes |
| KB-6165GC | ~150°C | Halogen-free lead-free | Yes | Yes | Yes |
| KB-6165GMD | ~155°C | Halogen-free mid-loss | Yes | Yes | Yes |
✓ = Verified from official Kingboard datasheet
KB-6165C and KB-6165LE occupy niche positions. KB-6165C serves customers who need halogen-free compliance without the "G" (green) resin system—typically legacy approvals or specific OEM material lists. KB-6165LE targets applications where even KB-6165F's Z-CTE of 3.0% is insufficient and designers need the absolute minimum achievable expansion within the mid-Tg class.
KB-6165C Specifications and Halogen-Free Compliance Details
KB-6165C specifications are estimated based on the KB-6165 verified datasheet with halogen-free resin modifications. Halogen-free materials typically show slightly higher Td values due to the absence of brominated flame retardants, which decompose at lower temperatures.
| Property | KB-6165C (Estimated) | KB-6165 (Verified ✓) |
|---|---|---|
| Tg (DSC) | ~150°C | 153°C |
| Td (TGA 5%) | ~340°C | 335°C |
| T-260 | ~45 min | 50 min |
| T-288 | ~20 min | 23 min |
| Z-CTE 50–260°C | ~3.0% | 3.1% |
| Z-CTE Alpha 1 | ~50 ppm/°C | 55 ppm/°C |
| Dk @ 1 GHz | ~4.5 | 4.5 |
| Df @ 1 GHz | ~0.015 | 0.016 |
| Anti-CAF | Yes | Yes (≥1000h) |
| Bromine | <900 ppm | Standard brominated |
| Chlorine | <900 ppm | Standard |
| Antimony | Free | Present |
Halogen-free compliance standard: KB-6165C meets IEC 61249-2-21 requirements: bromine ≤900 ppm, chlorine ≤900 ppm, total halogens ≤1500 ppm. Antimony-free formulation ensures compliance with expanded substance restrictions required by certain automotive and medical OEMs.
KB-6165LE Specifications and Ultra-Low Expansion Performance
KB-6165LE ("LE" = Low Expansion) pushes the Z-axis CTE reduction to the limits of what mid-Tg epoxy chemistry can achieve. Through aggressive filler loading and resin optimization, KB-6165LE targets Z-CTE values below 2.5% (50–260°C), approaching the performance of high-Tg materials like KB-6167F (2.6% verified).
| Property | KB-6165LE (Estimated) | KB-6165F (Verified ✓) | KB-6167F (Verified ✓) |
|---|---|---|---|
| Tg (DSC) | ~155°C | 157°C | 175°C |
| Td (TGA 5%) | ~340°C | 346°C | 349°C |
| T-260 | >60 min | >60 min | >60 min |
| T-288 | >30 min | >30 min | >35 min |
| Z-CTE 50–260°C | ~2.3% | 3.0% | 2.6% |
| Z-CTE Alpha 1 | ~35 ppm/°C | 40 ppm/°C | 40 ppm/°C |
| Dk @ 1 GHz | ~4.7 | 4.6 | 4.6 |
| Df @ 1 GHz | ~0.016 | 0.016 | 0.016 |
| Cost Index | ~1.35× | 1.25× | 1.40× |
The tradeoff for KB-6165LE's ultra-low expansion is increased filler content, which raises the dielectric constant (estimated Dk ~4.7 at 1 GHz) and significantly increases drill bit wear compared to standard filled materials. The higher Dk impacts impedance calculations and may require trace width adjustments.
For applications where Z-CTE below 2.5% is mandatory at mid-Tg pricing, KB-6165LE is the only option in Kingboard's portfolio. If the design can accept high-Tg pricing, KB-6167F (Z-CTE 2.6%) or KB-6168LE (Z-CTE ~2.2%) may be preferable due to their broader availability and more extensive qualification history.
When Halogen-Free Compliance Is Actually Required
Not every market requires halogen-free materials. Understanding where the mandate applies helps avoid unnecessary cost:
Markets with mandatory or strongly preferred halogen-free requirements:
- European Union: While RoHS does not explicitly mandate halogen-free, the WEEE Directive and voluntary eco-labels (EU Ecolabel, Blue Angel) increasingly require it
- Japan: Most major Japanese OEMs (Sony, Panasonic, Toyota, Denso) have corporate halogen-free mandates across their supply chains
- Automotive (EU and Japan): IATF 16949 certified manufacturers increasingly require IEC 61249-2-21 compliance
- Medical devices (Class II/III): Some notified bodies and OEM purchasing specifications require halogen-free materials as part of biocompatibility documentation
Markets where halogen-free is typically not required:
- North American industrial and military: MIL-PRF-31032 and IPC-6012 do not mandate halogen-free
- Chinese domestic market: No current regulatory halogen-free mandate
- Cost-sensitive consumer electronics: Standard brominated FR-4 remains dominant for high-volume, low-margin products
If your design targets multiple markets and at least one requires halogen-free compliance, standardizing on halogen-free material across all regions can simplify supply chain management. The cost premium is typically 10–15%.
When Ultra-Low Expansion Justifies the Premium
KB-6165LE's Z-CTE of approximately 2.3% is necessary in a narrow range of applications:
High aspect ratio vias (>10:1): As aspect ratio increases, the total Z-axis expansion is distributed across a longer copper barrel with the same expansion force. At 10:1 aspect ratio on a 2.4 mm board, KB-6165LE generates approximately 55 µm of expansion versus 72 µm for KB-6165F—a 24% reduction that directly translates to longer via fatigue life.
Extreme thermal cycling requirements: Products specified for 2,000+ thermal cycles between -40°C and +125°C (common in automotive and aerospace) benefit from every incremental reduction in per-cycle Z-axis strain. KB-6165LE's lower Alpha 1 CTE (~35 ppm/°C) reduces the per-cycle via strain compared to KB-6165F (40 ppm/°C).
Large board thickness (>2.5 mm): On thick boards, even small percentage CTE differences translate to significant absolute expansion. A 3.2 mm board made with KB-6165LE expands approximately 74 µm at 260°C, while the same board in KB-6165F expands 96 µm.
For applications not meeting these criteria, KB-6165F (Z-CTE 3.0%) provides sufficient reliability at lower cost and with better availability.
KB-6165C vs KB-6165G vs KB-6165GC: Halogen-Free Comparison
Kingboard offers three halogen-free options at the mid-Tg level. Understanding the differences helps select the right one:
| Property | KB-6165C | KB-6165G ✓ | KB-6165GC |
|---|---|---|---|
| Resin System | Modified KB-6165 | Dedicated HF resin | Dedicated HF resin |
| Tg (DSC) | ~150°C | 155°C | ~150°C |
| Td (TGA) | ~340°C | 365°C | ~355°C |
| Z-CTE 50–260°C | ~3.0% | 2.8% | ~2.9% |
| Df @ 1 GHz | ~0.015 | 0.013 | ~0.014 |
| Anti-CAF | Yes | Yes | Yes |
| IPC Slash Sheet | — | 4101E/128 | — |
| Filled | No | Yes | Yes |
| Availability | Limited | Standard stock | Moderate |
| Cost Index | ~1.30× | 1.30× | ~1.30× |
✓ = Verified from official Kingboard datasheet
Our recommendation: For new halogen-free mid-Tg designs, KB-6165G is the preferred choice. It has a verified datasheet, superior Td (365°C), the lowest Df (0.013 at 1 GHz) of the three, excellent Z-CTE (2.8%), and standard availability. KB-6165C should only be specified when a customer's approved material list or legacy qualification specifically calls for it. KB-6165GC provides a middle ground with lead-free enhanced properties.
KB-6165LE vs KB-6168LE: Mid-Tg vs High-Tg Low Expansion
For designs requiring the absolute lowest Z-axis CTE, Kingboard offers low-expansion variants at both the mid-Tg and high-Tg levels:
| Property | KB-6165LE | KB-6168LE |
|---|---|---|
| Tg (DSC) | ~155°C | ~175°C |
| Td (TGA) | ~340°C | ~350°C |
| Z-CTE 50–260°C | ~2.3% | ~2.2% |
| T-260 | >60 min | >60 min |
| T-288 | >30 min | >30 min |
| Cost Index | ~1.35× | ~1.50× |
| Target Market | Mid-Tg price point | Premium reliability |
The Z-CTE difference between KB-6165LE (2.3%) and KB-6168LE (2.2%) is modest. The primary advantage of KB-6168LE is its higher Tg, which provides better performance under sustained elevated temperatures. For designs operating above 120°C ambient, KB-6168LE is the correct choice. For designs operating at moderate temperatures where cost matters more than Tg, KB-6165LE achieves nearly equivalent Z-CTE at a lower price point.
Manufacturing Considerations: Halogen-Free and Low-Expansion Processing Requirements
Both KB-6165C and KB-6165LE require additional attention during manufacturing:
KB-6165C (halogen-free): Halogen-free resins have different curing characteristics than standard brominated materials. The lamination profile typically requires higher cure temperatures (>190°C) and longer cure times (>60 min) to achieve full cross-linking. Desmear processing may require adjusted permanganate concentrations because halogen-free resins respond differently to chemical etching. Solder mask adhesion should be validated on first articles, as the surface chemistry of halogen-free substrates differs from standard FR-4.
KB-6165LE (high filler loading): The aggressive filler loading that enables ultra-low CTE significantly impacts drilling. Expect 20–25% faster drill bit wear compared to standard filled materials. Micro-via laser drilling may be affected by filler particle interference at the laser wavelength. Desmear processing needs extended etch times to clean heavily filled via walls. Registration accuracy benefits from the dimensionally stable substrate, but inner layer etching chemistry may need adjustment for the modified resin.
Lead time considerations: Both variants are specialty products with lower stocking levels than mainline materials like KB-6165F or KB-6165G. Typical lead times are 2–4 weeks for laminate availability versus 1–2 weeks for standard grades. Plan procurement accordingly.
Target Applications: EU Compliance, Automotive, and High-Reliability Industrial PCBs
KB-6165C target applications:
- Japanese automotive OEM supply chain (Toyota, Honda, Nissan tier-1 and tier-2 suppliers)
- European industrial automation (halogen-free mandates from Siemens, ABB, Schneider Electric)
- Medical device PCBs requiring halogen-free certification for biocompatibility documentation
- Consumer electronics marketed with environmental certifications (EPEAT, TCO Certified)
KB-6165LE target applications:
- High-count multilayer boards (16+ layers) with aspect ratios exceeding 10:1
- Automotive ECUs rated for 2,000+ thermal cycles at -40°C to +125°C
- Aerospace avionics boards with stringent via reliability requirements per IPC-6012 Class 3/A
- Server and storage backplanes with thick cross-sections (>3.0 mm)
For both variants, APTPCB provides full DFM review, material procurement, and quality documentation to support your qualification process.
How to Order KB-6165C and KB-6165LE PCBs from APTPCB
APTPCB can source both KB-6165C and KB-6165LE for prototype through production volumes. Because these are specialty variants, we recommend early engagement with our materials team to confirm current availability and lead times.
Upload your Gerber files and specify the required material grade. Our engineering team will verify material suitability, provide a stackup recommendation, and deliver a detailed quotation. For designs where the optimal material choice is unclear, we provide complimentary material selection guidance.