The press force is set, so why do some areas still under-laminate?
On FPC, rigid-flex and IC substrate lamination lines, engineers often face the same question: the press setting looks stable, yet local voids, poorly bonded coverlay or resin squeeze-out at panel edges keep coming back. The root cause is often not the press itself but the area the force actually lands on, and whether the cushion between the press plates and the stack can turn circuit height differences into more even contact. This article looks at lamination cushion pads from a pressure-resistance angle.
Product confirmation: FPC Lamination Silicone Buffer Pad
The product discussed here is the Lixing FPC Lamination Silicone Buffer Pad (FPC金色矽膠緩衝墊). According to the official product page, it is a multilayer composite of high-elastic PTFE fiber fabric, high-temperature heat-conductive fluororesin and high-tensile fiberglass cloth, finished with a Teflon nano-coating as the anti-stick layer. It is positioned as a reusable lamination consumable that replaces traditional kraft paper and silicone pads.
Engineering pain points and failure modes
Pressure-related problems usually appear in three ways. First, the loaded area is smaller than expected, so local stress exceeds the cushion’s design range and the material is over-compressed. Second, copper traces, coverlay openings or stiffeners create height differences; a rigid pad touches only the high points and leaves low areas without pressure. Third, heat and repeated pressing change the material over its service life, so lamination quality drifts with cycle count.
Mechanism 1: stress depends on force and the actual loaded area
The press shows total force, but the material responds to force per unit area. When a small panel sits on a large platen, or only part of the platen carries the stack, the same total force concentrates on a smaller area and local stress rises. Compare a cushion pad’s pressure rating with stress in the same unit, not with press tonnage.
Engineering formula
Formula: σ = F⊥ / A
- σ: compressive stress, in Pa (N/m²); lamination shops often use kgf/cm²
- F⊥: force acting perpendicular to the loaded surface, in N
- A: area that actually carries the force, in m²
According to OpenStax University Physics Volume 1, Section 12.3 (a Rice University physics textbook), stress is force per unit area, and compressive stress uses the same definition as tensile stress; in the linear low-stress limit, stress = elastic modulus × strain, with strain equal to ΔL / L0. Applicability: estimating the nominal stress when total press force is spread over the actual loaded area, for a same-unit comparison with the pad’s pressure rating. Limitations: it gives only an average and ignores topography, edge effects and local concentration; a multilayer, viscoelastic pad at high temperature may not follow linear elasticity. The formula is an engineering model, not a product specification or performance guarantee.
Mechanism 2: a compressible layer turns height differences into contact pressure
Following the strain concept above, a material under load changes thickness by ΔL. A cushion pad compresses more over the higher parts of the stack while still reaching the lower areas, so pressure extends between traces and to coverlay edges; a rigid material tends to press only the peaks. The official page pairs a hardness of 85–90 Shore A with a multilayer fiber-cloth structure to describe a balance of support and even load distribution.
Mechanism 3: temperature and cycle count affect pressure stability
Hot lamination applies heat and pressure together, so pressure resistance cannot be judged from a single number. The official page lists a 280°C working temperature and a service life of approximately 600 cycles, depending on process, which means real life depends on the temperature profile, pressure and cycle time. A practical approach is to log cycle counts and periodically check thickness and the anti-stick surface rather than assume every press cycle is identical.
Core technical points
- Pressurization: officially listed as > 45 Kg/cm², a reference point for nominal stress comparison.
- Hardness: 85–90 Shore A, balancing support and conformity to stack topography.
- Working temperature: officially listed as 280°C for hot-press process evaluation.
- Structure: multilayer PTFE fiber fabric, heat-conductive fluororesin and high-tensile fiberglass cloth.
- Surface: Teflon nano-coating anti-stick layer, reusable for approximately 600 cycles depending on process.
Industrial applications
According to the official data, the pad is intended for lamination of PCBs, FPCBs, rigid-flex boards, IC substrates, HDI and high-frequency/high-speed boards. Lixing also recommends pairing it with silicone iron pads for structural support and even heat distribution, FPC green cushioning pads for local pressure compensation, and PTFE film tapes and polyimide tapes for edge protection and insulation.
Selection and design reminders
- Calculate σ with the area A that actually carries the stack, not the platen area.
- Keep a margin when comparing nominal stress with the official rating, and allow for local concentration.
- Confirm the temperature profile stays within the official working temperature and keep cycle-count and thickness records.
- Confirm size, thickness and pairing with Lixing for the actual model and process.
Conclusion
Good lamination depends on putting force on the right area and letting the cushion layer turn height differences into more even contact. Estimate nominal stress with σ = F⊥ / A, then check it against the official pressure, temperature and service-life data to turn under-lamination from guesswork into a checkable selection process. To review your stack-up, see the FPC Lamination Silicone Buffer Pad product page and discuss actual conditions with the Lixing technical team.
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