PP-1080 Prepreg for Thin PCB Build-Up: Specs & Selection Guide

When you need to shave 40–50 µm off a dielectric layer without sacrificing resin fill performance, PP-1080 thin prepreg is the material that comes up in almost every stackup conversation. It sits between the ultra-light 106 style and the mid-weight 2116 style in the glass fabric family — thin enough to support fine-pitch BGA breakout and HDI build-up layers, yet substantial enough to carry meaningful resin volume for reliable inter-layer bonding. For any engineer designing boards that need controlled outer dielectric thickness, tight impedance on narrow traces, or sequential lamination build-ups in the 60–90 µm range, 1080 is the fabric to understand in detail.

This guide covers the glass construction, the resin content grades, the full electrical and mechanical property set, and the specific stackup situations where PP-1080 thin prepreg is the correct call. It also addresses the less-discussed limitations of 1080 — particularly its asymmetric weave and what that means for differential pair skew at higher data rates. Engineers working with Doosan PCB laminates will find that 1080 prepreg pairs directly with the DS-7409CAF and ILD-series laminate families for fine-pitch and high-reliability build-ups.

What Is PP-1080 Prepreg? Glass Construction and B-Stage Basics

PP-1080 prepreg is a B-stage composite built on IPC/NEMA 1080 woven E-glass fabric, pre-impregnated with a partially cured epoxy resin system. The “1080” designation identifies the glass fabric style — not a resin product line or a supplier designation. Isola, Panasonic, Shengyi, and Nan Ya all make 1080-style prepreg; the base fabric comes from E-glass yarn woven to IPC-4412B specifications, but the resin formulation, treater conditions, and resulting Dk/Df values differ between manufacturers.

The 1080 fabric is woven from ECE-type E-glass yarn at 60 ends per inch in the warp direction and 47 picks per inch in the fill direction. This 60×47 thread count is the detail that experienced engineers pay close attention to — the warp and fill directions are notably asymmetric, which has practical consequences for differential pair routing that the article addresses directly below. Base fabric weight is approximately 49 g/m² (1.44 oz/yd²), and raw fabric thickness is approximately 0.064 mm (2.5 mil) before resin impregnation.

PP-1080 Thin Prepreg in the Glass Style Family

Understanding where PP-1080 thin prepreg sits relative to the other common styles shapes every stackup decision correctly.

Glass Style	Thread Count (warp × fill, ends/in)	Fabric Weight (g/m²)	Bare Fabric Thickness	Typical Resin Content	Cured Thickness Range	Dk @ 1 GHz
106	56 × 56	~25	~0.038 mm	~70–76%	~50–60 µm	3.9–4.1
1080	60 × 47	~49	~0.064 mm	~60–70%	~60–90 µm	4.0–4.3
2116	60 × 58	~109	~0.089 mm	~50–57%	~100–132 µm	4.3–4.6
7628	44 × 31	~203	~0.173 mm	~42–52%	~170–200 µm	4.5–4.9

The 1080 style’s defining characteristics — light fabric weight with high resin content, thin but not ultra-thin per ply, and lower Dk than the mid-weight styles — make it the natural default for thin outer and inner build-up layers in standard and HDI multilayer designs.

PP-1080 Thin Prepreg Electrical and Mechanical Properties

Electrical Properties by Resin Grade

PP-1080 thin prepreg is available in three resin content grades: Standard Resin (SR), Medium Resin (MR), and High Resin (HR). The grade determines pressed thickness, resin flow during lamination, and — because the resin has lower Dk than the glass — the effective post-lamination Dk of the dielectric layer.

Property	SR (~60–62%)	MR (~63–65%)	HR (~64–66%)	Test Method
Resin Content	60–62%	63–65%	64–66%	IPC-TM-650 2.3.16
Cured Thickness / ply (1 oz Cu, ~80% coverage)	~60–68 µm	~68–78 µm	~75–90 µm	IPC-TM-650 2.4.39
Dk @ 1 GHz	~4.1–4.3	~4.0–4.2	~3.9–4.1	IPC-TM-650 2.5.5.5
Dk @ 5 GHz	~3.9–4.1	~3.8–4.0	~3.7–3.9	IPC-TM-650 2.5.5.5
Dk @ 10 GHz	~3.8–4.0	~3.7–3.9	~3.6–3.8	IPC-TM-650 2.5.5.5
Df @ 1 GHz	~0.015–0.018	~0.015–0.018	~0.015–0.018	IPC-TM-650 2.5.5.5
Resin Flow	Low	Medium	High	IPC-TM-650 2.3.17
UL 94 Flame Rating	V-0	V-0	V-0	UL 94

The higher resin content of 1080 compared to 2116 means that 1080 MR/HR typically shows a slightly lower post-lamination Dk than 2116 SR. This is worth noting when designing hybrid stackups where 1080 and 2116 coexist in different dielectric positions — the Dk difference must be accounted for independently in each dielectric section’s impedance model. A common mistake is using a single FR-4 Dk value for the whole stackup when glass styles are mixed.

Mechanical and Thermal Properties

Property	Typical Value	Test Method
Glass Transition Temperature (Tg, standard)	≥130–150°C	IPC-TM-650 2.4.25 (DSC)
Glass Transition Temperature (Tg, high-Tg grade)	≥170–180°C	IPC-TM-650 2.4.25
Decomposition Temperature (Td)	≥300–340°C	IPC-TM-650 2.4.24.6
T-260 (time to delamination at 260°C)	>5 min (standard); >30 min (high-Tg)	IPC-TM-650 2.4.24.1
Z-axis CTE (below Tg)	~50–60 ppm/°C	IPC-TM-650 2.4.41
Peel Strength (1 oz Cu)	≥1.0 N/mm	IPC-TM-650 2.4.8
Water Absorption	≤0.35%	IPC-TM-650 2.6.2
Shelf Life (≤23°C, <50% RH, in original packaging)	~3–6 months	Manufacturer guidance

The higher resin content of 1080 means the fabric contributes proportionally less to mechanical stiffness than in heavier styles — which is perfectly fine for thin dielectric applications but means that stacking more than three plies of 1080 between cores adds little mechanical benefit beyond what two plies provide. For any dielectric section requiring more than ~200 µm, the correct approach is to use a 2116 or introduce a core rather than stacking 1080 plies.

Why PP-1080 Thin Prepreg Is the Go-To for These Specific Design Situations

#### Thin Outer Dielectric Build-Up for Narrow-Trace Impedance

The most direct application for PP-1080 thin prepreg is as the outer dielectric where trace widths must be narrow — typically below 3.5 mil (0.089 mm) — to meet 50 Ω microstrip or 100 Ω differential microstrip targets. The relationship is straightforward: thinner dielectric requires narrower traces for the same characteristic impedance. On a standard 4-layer 1.6 mm board with 2 × 1080 MR outer dielectric (~140 µm combined), a 50 Ω microstrip requires approximately 3.0–3.5 mil trace width, whereas 2 × 2116 MR (~230 µm combined) requires approximately 4.5–5.5 mil. The 1080 option opens up an extra ~1.5 mil of trace width margin — useful on fine-pitch BGAs where that margin is the difference between a routable and an unroutable escape channel.

HDI Build-Up Layers in Sequential Lamination

In HDI boards with 1+N+1 or 2+N+2 build-up structures, the dielectric between the outermost copper layer and the first internal layer typically targets 50–100 µm — thin enough to support the aspect ratio of laser-drilled microvias while keeping the microvia diameter manufacturable. PP-1080 thin prepreg in HR grade at ~75–90 µm per ply is the standard material for these build-up positions. It provides sufficient resin volume to fill the micro-relief of the inner copper without flowing onto adjacent via pads, and the pressed thickness per ply remains predictable enough to hold ±10 µm tolerance across a production panel — critical for microvia aspect ratio and laser depth control.

Combining PP-1080 With 2116 to Fine-Tune Stackup Thickness

One of the most practical uses of PP-1080 thin prepreg is as the tuning element in a hybrid stackup. The arithmetic is simple: a 2116 MR ply gives ~120 µm, a 1080 MR ply gives ~73 µm. A 2116 MR + 1080 MR combination gives approximately 190–195 µm — a thickness not achievable with a single ply of either material. This combination is widely used on standard 6-layer 1.6 mm FR-4 designs where the inner signal-layer dielectric needs to hit a specific target for controlled impedance without the cost of moving to thinner core.

A typical 6-layer 1.6 mm FR-4 hybrid stackup example:

Layer	Material	Approximate Pressed Thickness
L1 copper	0.5 oz + plating	~35 µm
Dielectric L1–L2	1 × 2116 MR + 1 × 1080 MR	~193 µm
L2 copper (GND)	0.5 oz	~18 µm
Core (L2–L5)	FR-4 0.7 mm core	~700 µm
L5 copper (PWR)	0.5 oz	~18 µm
Dielectric L5–L6	1 × 2116 MR + 1 × 1080 MR	~193 µm
L6 copper	0.5 oz + plating	~35 µm
Total		~1.19 mm → target core adjusts to ~1.6 mm final

The 2116 + 1080 outer pair is the combination most volume fabricators stock and press reliably — it is a well-characterised material combination with good published press-out data from Isola, Panasonic, and Shengyi.

The 1080 Weave Asymmetry Problem: What It Means for Differential Pairs

This is the section of the 1080 story that gets skipped in introductory articles but matters significantly on designs running above 3–5 Gbps. The 1080 fabric has an asymmetric weave: 60 ends per inch in the warp direction versus 47 picks per inch in the fill direction. This unevenness means the “resin windows” — the areas between glass bundles where resin fills the fabric — are noticeably elongated in the fill direction. A differential pair routed in the warp direction will see a different periodic Dk variation pattern than a pair routed in the fill direction. At high data rates, this leads to measurable propagation skew between the P and N legs of a differential pair, degrading the differential signal eye opening.

Intel’s PCB stackup guidelines for FPGA designs specifically note that for high-speed signal layers, the 1080 style is a reasonable cost-performance compromise but recommend zig-zag routing at a small angle relative to the glass strands to average out the on-weave and off-weave sections. Alternatively, at data rates above 10 Gbps, consider substituting a more symmetric glass style — 2116 (60×58 threads) or 1086 — for the specific dielectric layers adjacent to the critical high-speed signal layers, and retain 1080 for the other less-critical layer positions.

The article “Why You Should Quit Using 1080 Glass” by Bill Hargin at Z-zero provides quantitative data on the resin window size and GWS implications of 1080 versus alternatives such as 1078 and 1086 — worth reviewing for designs above 5 Gbps where skew budget is tight.

PP-1080 Thin Prepreg vs. Other Thin Glass Styles: Direct Comparison

Property	PP-106	PP-1080	PP-2116
Cured thickness / ply	~50–60 µm	~60–90 µm	~100–132 µm
Resin content	~70–76%	~60–66%	~50–57%
Dk @ 1 GHz	~3.9–4.1	~4.0–4.3	~4.3–4.6
Weave symmetry	Near-square (56×56)	Asymmetric (60×47)	Near-square (60×58)
GWS risk at >5 Gbps	Moderate	Moderate–High	Low
Resin fill for 0.5 oz Cu	Excellent	Excellent	Good
Resin fill for 1 oz Cu	Adequate (HR recommended)	Excellent	Excellent
HDI build-up use	Yes (ultra-thin)	Yes (standard build-up)	Not typical
Standard availability	Good	Universal	Universal
Relative cost per ply	Low	Low–moderate	Moderate

Storage, Handling, and Shelf Life

PP-1080 thin prepreg has a slightly longer shelf life than 2116 under equivalent storage conditions — typically three to six months from manufacture when stored below 23°C and at relative humidity of 50% or lower, in original moisture-barrier packaging. The higher resin content of 1080 makes it somewhat more resilient to marginal storage conditions compared to SR-grade 2116, but that extra margin is not a reason to be careless. Moisture uptake in prepreg advances the cure state, reduces resin flow on the press, and introduces void risk at thinner pressed thicknesses where there is less resin volume to compensate for flow irregularities.

Before any production run using PP-1080 thin prepreg, a qualified fabricator will run incoming gel time and flow tests. If gel time has shortened significantly from the nominal value on the CoA, the material should not be used — pressing short-gel-time 1080 is one of the more reliable ways to introduce microlamination voids that only reveal themselves at cross-section.

Avoid exposing PP-1080 thin prepreg to UV light during handling — even indirect sunlight at a layup station for extended periods will advance the cure state and affect flow. Keep sheets covered until immediately before use.

Useful Resources for PP-1080 Thin Prepreg Specification

Resource	Description	URL
Isola IS410 / IS420 Prepreg Datasheet	Full Dk/Df frequency tables for 1080 and other glass styles across 100 MHz–10 GHz	isola-group.com
Panasonic R-1755W Datasheet	Construction data for 1080 + 2116 hybrid builds including pressed thickness tables	industrial.panasonic.com
IPC-4101F Base Materials for Rigid and Multilayer Printed Boards	Qualification and acceptance spec for FR-4 prepregs, including 1080 glass constructions	ipc.org
Z-zero Stackup Planner	Web-based stackup tool using supplier-specific Dk/Df per glass style and resin grade — correctly handles mixed 1080/2116 dielectric positions	z-zero.com
PCDandF “Why You Should Quit Using 1080 Glass” (Bill Hargin)	Quantitative analysis of 1080 glass weave asymmetry, resin windows, and GWS impact; includes 1078/1086 alternatives	pcdandf.com
Intel AN528 PCB Dielectric Material Selection and Fiber Weave Effect	Detailed fiber weave skew analysis including 1080 and 2116 glass styles at high data rates	intel.com
PCBSync Prepreg Selection Guide	Practical guide to glass styles, resin grades, and stackup decision-making	pcbsync.com
Altium Designer Stackup Manager	Integrated PCB layer stack tool with prepreg Dk/Df import from supplier libraries	altium.com

5 FAQs: PP-1080 Thin Prepreg in PCB Design and Fabrication

Q1: When should I use PP-1080 thin prepreg instead of 2116 in my outer build-up?

The trigger is trace width. If your 50 Ω microstrip trace width on the outer layer needs to be below approximately 4 mil (0.10 mm) to fit within the routing geometry — typically driven by fine-pitch BGA escape channels or high-density trace patterns — then an outer dielectric in the 60–90 µm range achievable with 1080 MR/HR gives you the spacing you need. With 2 × 2116 MR giving ~230 µm outer dielectric, a 50 Ω microstrip typically needs ~4.5–5.5 mil. With 2 × 1080 MR giving ~150 µm, that same 50 Ω target requires approximately 2.5–3.5 mil. The caveat is that narrower traces push toward the etch tolerance limits of your fab house, so always confirm minimum trace width capability before committing to the 1080-based outer build. A second driver for 1080 outer build is overall board thinning — boards targeting total thickness below 1.2 mm will typically require thinner outer dielectrics, and two plies of 1080 rather than 2116 is the first adjustment to make before touching the core.

Q2: What Dk value should I use for PP-1080 thin prepreg in my impedance calculations?

The same warning that applies to 2116 applies here with equal force: do not use the generic “FR-4 Dk = 4.2” in your impedance calculator. For PP-1080 MR, the post-lamination Dk at 1 GHz is typically 4.0–4.2. At 5 GHz it drops to approximately 3.8–4.0, and at 10 GHz to approximately 3.7–3.9. These values are meaningfully lower than equivalent 2116 values, which is why mixed-style stackups must use separate Dk entries for each dielectric layer — not a single blended value. The correct workflow is to pull the frequency-resolved Dk/Df table from your specific supplier’s datasheet for the exact 1080 product and resin grade, enter that into your impedance calculator, and then confirm the target trace width with your fabricator’s empirical press-out data. Many experienced fabricators maintain in-house pressed Dk calibration values that differ slightly from the raw material datasheet values — always ask for them.

Q3: Can I use PP-1080 thin prepreg for the dielectric layers adjacent to high-speed differential pairs above 5 Gbps?

You can, but you should be aware of the limitation. The 1080 glass style has an asymmetric thread count (60×47) which produces larger, elongated resin windows between glass bundles. At data rates above 3–5 Gbps, differential pairs routed with one conductor landing on a glass bundle and the other landing on a resin window can accumulate enough propagation skew to erode the eye opening — an effect called glass weave skew (GWS). The practical mitigation is to route differential pairs at a small angle (typically 5–15°) relative to the glass strands, which distributes both conductors across a mix of on-weave and off-weave sections and averages the Dk variation. For designs firmly above 10 Gbps where GWS budget is tight, consider using 2116 (60×58, near-square) or mechanically-spread glass (1086, 1078) specifically on the signal-adjacent dielectric layers, while retaining 1080 on non-critical positions to manage cost.

Q4: Is there a maximum number of PP-1080 thin prepreg plies I should stack in one dielectric section?

The practical maximum is three plies, and the common working maximum is two. Three plies of 1080 HR gives approximately 225–270 µm pressed thickness — at that point a single ply of 2116 or a thin FR-4 core provides equivalent or better dimensional stability at lower cost and void risk. Stacking three 1080 plies also concentrates a significant volume of B-stage resin in one location, increasing the risk of uneven resin flow during pressing, particularly across large panel formats (18×24 inches) where press temperature uniformity is harder to control. If your stackup genuinely requires 200+ µm of dielectric in a single position, the right call is to use a 2116 ply rather than three 1080 plies — it gives a more predictable pressed thickness and costs less per unit area in most supply chains.

Q5: Does high-Tg PP-1080 thin prepreg have different Dk and Df values compared to standard-Tg 1080?

Yes, and this matters for impedance-controlled designs. High-Tg 1080 prepreg uses a modified resin chemistry — typically a phenolic-cured or dicy-free epoxy system — that replaces the standard dicyandiamide-cured FR-4 resin to achieve Tg ≥ 170°C. The phenolic resin system typically shows Dk values approximately 0.1–0.2 units lower than standard mid-Tg 1080 at 1 GHz, and Df that is broadly similar or marginally higher. Halogen-free 1080 variants introduce phosphorus-based or inorganic flame retardant in place of brominated compounds, which also shifts Dk slightly depending on the specific flame retardant loading. The practical implication: if your impedance-controlled board is being built on high-Tg or halogen-free 1080 prepreg — as is common for lead-free assembly, automotive, or industrial applications — run a separate impedance calculation using the grade-specific Dk/Df table from your supplier. Carrying over the standard-Tg Dk value to a high-Tg or halogen-free build is a common source of first-article impedance failures, particularly at ±5% IPC-6012 Class 3 tolerance.