Learn why PP-2116 prepreg is the standard choice for PCB build-up layers. This engineer’s guide covers key specs, stack-up examples, resin grades (SR/MR/HR), storage rules, comparison tables vs. 1080 and 7628, and useful datasheets — everything you need to make the right material call.

If you’ve been doing multilayer PCB stack-up work long enough, you already know that material selection is rarely glamorous — but it matters enormously. One material that comes up in almost every build-up conversation is PP-2116 prepreg. Walk into any mid-to-high volume PCB fab and the odds are strong that 2116 is sitting in the lamination room as the default go-to. This guide breaks down exactly why that is, what the numbers mean, and when you should — or shouldn’t — reach for it.

What Is PP-2116 Prepreg?

Prepreg (short for “pre-impregnated”) is fiberglass cloth saturated with a partially cured epoxy resin system, held in what’s called a B-stage cure state. It stays pliable and slightly tacky until you hit it with heat and pressure in the lamination press — at which point the resin flows, fills the copper relief, and cures into a solid dielectric layer bonding everything together.

The number “2116” refers to the IPC glass fabric style — a mid-weight E-glass weave with a specific thread count and construction. Mid-weight styles like 2116 provide a balance between cost, mechanical properties, and electrical performance, making them workhorses for most standard multilayer PCBs.

Think of it as the 18-gauge wire of the PCB materials world — not the thinnest, not the thickest, but reliable enough to cover the majority of real-world applications without breaking the bank.

PP-2116 Prepreg Key Technical Specifications

PP 2116 has a thickness range of 90–110 μm, a dielectric constant (Er) of 3.6–3.8, and a resin content of approximately 50%. These values shift slightly depending on the supplier and resin grade, so always verify against the specific datasheet you’re designing to.

Parameter	PP-2116 (Typical)	PP-1080 (Typical)	PP-7628 (Typical)
Glass Fabric Style	2116	1080	7628
Cured Thickness (μm)	90–110	60–70	170–190
Resin Content (%)	~50	~60	~45
Dk (Er) @ 1 GHz	3.9–4.2	~3.5	4.1–4.6
Dissipation Factor (Df)	~0.020	~0.018	~0.022
Typical Application	Standard build-up layers	High-density / high-speed	Thick filler / cost-sensitive
Relative Cost	Medium	Medium-Low	Low

Resin grades are also available within the 2116 style:

Grade	Resin Content	Flow Behavior	Best Used For
SR (Standard Resin)	~50–52%	Low flow	Plane-to-plane bonding, stable geometry
MR (Medium Resin)	~52–56%	Moderate	General signal layer builds
HR (High Resin)	~56–60%	High flow	Heavy inner copper (2 oz+), filling etched areas

2116SR prepreg (≈50% resin) is ideal for plane-to-plane bonding applications, while the HR grade is better suited where you need aggressive resin fill around thick copper traces.

Why PP-2116 Prepreg Dominates Build-Up Layers

Balanced Dielectric Thickness for Impedance Control

One of the most practical reasons 2116 shows up in almost every standard stack-up is the dielectric thickness it produces after pressing. For lower routing densities and higher current requirements, 2116 and 7628 allow for traces 8 to 14 mils in width. That range sits comfortably in the sweet spot for most controlled impedance designs — 50Ω microstrip and stripline are both achievable without exotic trace widths.

In a typical 4-layer 1.6mm board, the stack-up using 1 oz Cu and two sheets of 2116 pre-preg on each side of the core would produce a spacing between the top layer and the signal core finishing at about 9.3 mils. That’s a well-characterized, repeatable geometry that makes impedance modeling reliable.

Industry-Standard Stack-Up Compatibility

In standard pool fabrication, prepreg types including PR2116 (120 μm) are among the standard prepregs used for predefined build-ups alongside PR1080 (70 μm) and PR7628 (180 μm). The fact that major PCB pool services carry 2116 as a standard material means your design is more likely to be manufactured without substitution flags or material surcharges — important when you’re doing quick-turns.

Mechanical Stability and Resin Flow

The 2116 weave is tight enough to give you good dimensional stability during pressing, while still providing enough resin to fill relief around inner-layer copper. This balance is why 2116SR is preferred for plane-to-plane bonding applications — the controlled flow reduces squeeze-out and keeps dielectric thickness consistent across the panel.

Compatibility with Doosan PCB Materials

Doosan PCB materials, including their popular DS-7409 series, are widely used with the 2116 glass style. Doosan’s epoxy systems are formulated to work predictably within standard 2116 press cycles, which makes them a common choice in fabrication shops already qualified on FR-4 processes. When specifying Doosan-based laminates, the 2116 prepreg format integrates directly into existing lay-up procedures without requiring changes to press recipes or oxide treatment lines.

PP-2116 vs. Other Prepreg Styles: When to Switch

Choosing the right prepreg isn’t just about picking the default — here’s how to think through alternatives:

Situation	Recommended Prepreg	Reason
Standard 4–8 layer FR-4 board	2116	Best all-round balance
High-speed signal layers (>5 GHz)	1080 or 3313	Lower Dk, smoother surface, reduced fiber weave effect
Heavy copper (2 oz+) inner layers	2116HR or 1080HR	Higher resin fill to cover copper relief
Very thick filler dielectric	7628	Thicker single-ply, lower cost
Cost-driven, low-layer-count board	7628	Lower material cost
Controlled impedance on thin builds	1080	Thinner pressed dielectric

Lightweight styles like 1080 are preferred for high-frequency applications where lower Dk improves signal propagation, so if you’re routing >5 GHz differential pairs, moving to a 1080-based dielectric on those critical layers makes sense — while keeping 2116 everywhere else.

PP-2116 Prepreg in Multilayer Stack-Up Design

4-Layer Board Stack-Up Example

A common 1.6mm 4-layer build using 2116:

Layer	Material	Thickness
L1 (Top)	1 oz Cu foil	35 μm
Dielectric	2× PP-2116	~200–220 μm
L2	Inner copper (etched)	17 μm
Core	FR-4 core	~900 μm
L3	Inner copper (etched)	17 μm
Dielectric	2× PP-2116	~200–220 μm
L4 (Bottom)	1 oz Cu foil	35 μm

6-Layer Board Stack-Up Example

For a 6-layer 1.6mm design, 2116 is typically used for the outer build-up dielectrics while thinner 1080 or the core itself handles the inner signal spacing:

Layer	Material	Notes
L1 / L6 outer dielectric	1–2× PP-2116	Controls outer microstrip impedance
Inner signal dielectrics	1080 or thin core	Tighter spacing for stripline control
L3/L4 separation	Core material	Provides rigid center

Engineer’s tip: Never stack more than 3 sheets of prepreg between layers. In practice, it is not recommended to stack more than 3 sheets of prepreg together — resin squeeze-out becomes uncontrollable and you’ll see thickness variation across the panel.

Storage and Handling: Don’t Wreck Your Material

Before using prepregs for PCB manufacturing, they should be stored in special conditions: beware of moisture, always keep wrapped in damp-proof material. Keeping in normal conditions, prepreg might absorb moisture and its bonding strength would be weakened. Avoid UV-rays and strong light.

Practically speaking, your PP-2116 rolls should live in a temperature-controlled, humidity-monitored storage room — ideally below 23°C and at 40–60% RH. If the prepreg is not consumed within 48 hours after opening the vacuum package, it is recommended that the bags be resealed. Expired prepreg that’s absorbed moisture will delaminate — often intermittently, which is the worst kind of failure to chase down.

Standard shelf life for most PP-2116 materials is 3–6 months from the manufacture date, depending on the supplier’s resin system. Always check the date stamp on the roll end label before pulling it for a production run.

Useful Resources for PP-2116 Prepreg

Here are some reference links engineers frequently use when working with 2116 prepreg stack-ups:

• IPC-4101 – Specification for Base Materials for Rigid and Multilayer Printed Boards. The foundational standard for prepreg classification: https://www.ipc.org/ipc-4101
• Isola Group Prepreg Datasheets (IS410, IS420, 370HR) — includes 2116 pressed thickness and Dk data: https://www.isola-group.com/products/all-printed-circuit-board-materials/
• Shengyi Technology Prepreg Database — widely used in Asian fabs, data available for S1000-2 and S1170 in 2116 style: https://www.sytech.com.cn
• Ventec VT-47 Process Guide — includes 2116 press thickness tables and lamination parameters: https://www.ventec-group.com/products/lead-free-assembly/vt-47/datasheet/
• PCBInternational Prepreg Thickness Chart — quick pressed-thickness reference in mils: https://www.pcbinternational.com/tech/prepegthicknesschart/
• Saturn PCB Toolkit — free stack-up calculator, supports 2116 and other standard styles: https://saturnpcb.com/saturn-pcb-toolkit/

Frequently Asked Questions About PP-2116 Prepreg

Q1: Can I substitute PP-2116 with PP-2125 in my existing stack-up?

Not directly. The thickness of 2116 differs from 2125 by approximately 20 μm — and in a standard 6-layer board that used 7 sheets of this type, the thickness difference resulted in an unexpected, often too-thick final board. Always recalculate your stack-up if switching between these styles.

Q2: What Dk value should I use for PP-2116 in impedance calculations?

Use post-lamination Dk values from your specific supplier’s datasheet — not the raw prepreg Dk. The dielectric constant Er for 1× Prepreg 2116 is approximately 4.20 as a typical starting point, but this changes based on copper coverage on adjacent layers. Always run calculations with both signal-adjacent (lower Dk) and ground-adjacent (higher Dk) values.

Q3: How many sheets of PP-2116 can I use between layers?

A maximum of 3 sheets is the practical limit. Beyond that, resin flow becomes difficult to control and you’ll see dielectric thickness inconsistency. Two sheets of 2116 is most common for outer build-up layers on standard 4- and 6-layer boards.

Q4: Is PP-2116 suitable for high-speed designs?

It’s usable up to around 5 GHz in most situations, but the fiber weave pattern can cause periodic Dk variations along a trace — known as fiber weave effect. For critical >5 GHz differential pairs, consider moving to 1080 or mechanically rotating/offsetting the weave at 45° to reduce this effect.

Q5: Does PP-2116 come in halogen-free versions?

Yes. Most major suppliers — including Isola, Shengyi, Panasonic (Megtron), and Doosan — offer halogen-free 2116 prepreg meeting IEC 61249-2-21. These use phosphorus-based flame retardants and typically carry slightly different Dk/Df values compared to standard FR-4, so update your impedance models accordingly.

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Learn why PP-2116 prepreg is the standard choice for PCB build-up layers. This engineer’s guide covers key specs, stack-up examples, resin grades (SR/MR/HR), storage rules, comparison tables vs. 1080 and 7628, and useful datasheets — everything you need to make the right material call.

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Shorter version (155 chars): PP-2116 prepreg is the go-to choice for multilayer PCB build-up layers. Explore specs, stack-up examples, resin grades, and expert selection tips in this guide.