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What is a micro-via?

It’s a metalized hole buried (inner layer) or blind (outer layer) between two adjacent copper foils done by laser.

What does stack via or ELIC mean?

ELIC is the acronym for Every Layer Interconnect. Stacked via micro-vias filled with copper. They are located at the same position layer to layer to create metalized blind or buried holes with a smaller diameter than via done by the mechanical drill bit.

What is the aspect ratio for micro-via?

The aspect ratio for laser micro via is from 0.8:1 to 1.25:1. Common value is 8:1.

What is the minimum and maximum micro-via size?

The diameter range is from 0.15 mm to 0.075mm. The common diameter is 0.1mm. 0.06mm can be done as samples.

What does HDI stand for?

HDI is the acronym for High-Density Interconnect. A PCB with multiple levels of micro-vias, thin trace & space provides higher signal density to achieve better signal integrity than standard multi-layers PCB. HDI PCBs provide interconnection of low-pitch packages and much higher component population density.

Flex & Rigid-Flex

Why choose Flex or Rigid Flex assembly?

Rigid-Flex PCB offers a rigid zone that is suitable for component assembly (SMT or THT).

Is HDI suitable for Rigid-flex PCBs?

HDI build is suitable on the FR4 areas of a rigid-Flex PCB.

What is a semi-flexible PCB?

Semi-Flex PCBs are made from FR4 material, in which some areas are thinner enough to support a bending. It can be used only for static applications and for a limited number of bending.

What is a non-adhesive Polyimide raw material?

Usually, flexible PCBs are done by FCCL (Flexible Copper Clad laminate). FCCL is copper foils stacked to PI by adhesive. The adhesive is done by modified epoxy or acrylic resins whose electrical and thermal properties are not so good that their availability to support bends. Adhesive less FCCL is a copper bonded directly to the polyimide which alloys a better electrical and thermal performance, but the counterpart is that it’s less suitable for bending.

What are ED and RA copper?

ED is the acronym for Electro Deposed, and RA is for Rolled Applied. ED copper has better electrical properties and is suitable for static applications. RA copper has not so good electrical properties as ED but is more flexible than RA copper which is preferable for dynamic applications.

What are the main raw materials used for flexible PCBs?

Polyimide (PI) is the main material for Flexible and Rigid-flex PCBs. It could be with adhesive or adhesive less and with a thickness range from 12.5µ to 50µm. The cover sheet is done by solid coverlay (PI with an adhesive) or by photo-imageable flexible solder mask. Stiffeners (PI or FR4) are also available. PI has enough strength to support the PTH process and assembly process (SMT or THT). PET raw material (Polyester) is a cost-effective material used for single-side PCBs without SMT or THT assembly process.

What are the main stack-up options for flexible and rigid-flexible PCBs?

Flexible PCB is from 1 to 6 layers (1 to 3 flexible cores). Rigid-flex is from 1 to 6 flexible layers (1 to 3 flexible cores) and up to 26 layers in the rigid zone. Air-gap option is available to help to bend at flexible zones.

Surface finishes

What are the different types of gold finishes? ENIG, ENEPIG, EPIG, DIG, ISIG, Soft-Gold, Hard-Gold?

- ENIG: Electroless Nickel, Immersion Gold
- ENEPIG: Electroless Nickel, Electroless Palladium, Immersion Gold
- EPIG: Electroless Palladium, Immersion Gold
- DIG: Direct Immersion Gold
- ISIG: Immersion Silver, Immersion Gold
- Soft-Gold: Electrolytic Nickel, Electrolytic Gold
- Hard-Gold: Electrolytic Nickel, Electrolytic Gold / Cobalt

What are the different finishes?

The most common material used for PCBs finishes is a water-based chemical compound (OSP; Organic Solderability Preservative), Tin with HASL-LF, HASL, Immersion Tin, Gold with underlayer Nickel (ENIG, ENEPIG, EPIG, DIG, Soft-Gold, Hard-Gold), and Immersion Silver.

PCB Design rules

What does IPC mean?

IPC is the acronym of the Institute of Printed Circuits. IPC is a company that aims to standardize the production requirement of the electronic assembly industry. It’s the major reference in the PCB industry.

What is IC?

IC is the acronym for ionic contamination. When the ionic residues are too much, it may cause issues with reliability (corrosion and electrochemical migration like CAF or Dendrite). IPC-6012 defines the maximum level of IC as an equivalent of 1.56 µg/cm² NaCl. The common value is 0.8µg.

What is the minimum distance between the copper and the outline?

The minimal distance is 0.5mm for the inner layer and 0.35mm for the outer layer.

What is the influence of Gold Finger on the design of the PCB?

Gold-Finger is a Hard-Gold finish which is an electrolytic process that needs an electrical connexion to be performed.

What is the minimum thickness of the solder mask?

The minimum LPI (Liquid Photo Imageable) Solder Mask is 25µm which is equivalent to a minimum dielectric of 500 VDC.

What is the minimum diameter of the PTH without a solder mask?

The minimum PTH free of solder mask is 0.45mm.

Are Press-Fit holes suitable for PCBs?

Yes, the Automotive industry uses any press-fit technology. Common PTH tolerance is +/-50µm with copper tub thickness range from 25 to 35µm.

What is the minimum pad size for HDI?

The minimum pad is 150µm for the outer layer and 300µm for the inner layer.

What is the minimum track and space for the inner and outer layers?

The minimum track / Space is 75/75µm. Advanced capability is 60/60µm for the inner layer.

What is the copper thickness used in the PCB industry?

Base raw material common thicknesses are 1/3, 1/2, 1, 1.5, 2, and 3 Oz (1 Oz is 35µm copper thickness)


What is CAF?

CAF is the acronym for Conductive Anodic Filament. CAF is the electrochemical copper migration along the glass fiber which may result in a loss of dielectric or an internal short circuit in the material.

What does Oz stand for?

Oz (Once) is a unit of mass. 1 oz / Ft² = 305 gr / m² equivalent to 35 µm Copper thickness. This unit is used in the PCB industry. Common values are 1/3, 1/2, 1, 2, and 3 Oz.

What is Polyimide?

Polyimide is a base raw material used to manufacture Flex-PCBs. These properties allow built-in PTH and Hi-temperature for the reflow assembly process.

What is PTFE?

PTFE: Polytetrafluoroethylene is used as the base raw material for Teflon PCBs

What do UL and CUL stand for?

UL: Underwriters Laboratories is a certifying company that helps companies to demonstrate safety and sustainability and achieve regulatory compliance according to the USA market. CUL is for Canadian Underwriters Laboratories.

What are the different processes and colors of solder masks?

There are 2 main solder-mask processes. Silk-screen and spray. Both use the same photo-imageable process (films or direct imaging). The difference is how the solder mask is applied on the PCB surface. A large variety of colors are available: green, blue, red, white, and black, with different aspects: shiny, semi-gloss, or matte.

What is the maximum operating temperature?

Standard FR4 materials should be suitable for a maximum operating temperature of approximately 110°C. Special FR4 should be suitable up to 130°C.

What is a flame retardant?

Flame retardant is a chemical applied to raw material to slow the growth of a fire.

What is CTI?

CTI is the acronym for Comparative Tracking Index. It is used to measure the electrical breakdown properties of the insulating material. It is primarily used to assess electrical safety, especially for human users of electrical devices. Material manufacturers will provide these details in their material specifications sheet. Most of the FR4 CTI values are 150V. 250, 300, 600, and 900V are available.

What is low and ultra-low-loss material?

The lower the Dk (Dielectric Constant) of the dielectric raw material, the higher the availability to bring high-frequency signals to travel fast through the PCB with controlled impedance.

Via Holes

What is a countersink?

A countersink is a conical hole added to a drilled hole to allow the head of a countersunk screw to sit flush with the surface of the PCB.

What is an aspect ratio?

It is the ratio of the PCB thickness (base material + copper base) compared to the smallest hole diameter. A common value for Via and PTH is 12:1. Regarding micro-via (HDI laser via) common value is 1:1.

What is Back-Drilling?

Back-drill is a CNC drilling process that removes the non-functional part of the copper tub of a PTH. It helps to reduce signal attenuation and distortion for better signal integrity.

What is POVF?

POVF: Platted Over Via Filled. It’s a plugged via covered by copper. It’s referring to IPC as type VII via.

What is a plugged-via?

According to IPC standards, it’s a via filled with epoxy resin. It is defined by IPC from type III to type VII.

What is a via-hole?

A via hole is a PTH that is not used for THT (through-hole technology) assembly. The common diameter range is from 0.15mm to 0.45mm.

What is a "buried-via"?

Buried Vias are used in multi-layer boards where the inner layers need a connection, but the drilled hole is on the inner layers only and does not extend to the outer layers. To enhance reliability, we recommend plugging the buried holes with resin.

What is a blind-via?

Blind Vias are used in multi-layer boards where a drilled hole needs a connection from an outer layer to an inner layer where the hole must stop before the next layer. It is a non-through hole.

What is the minimum diameter of a mechanical drill?

Commonly minimal drill bit diameter is 0.15mm. Advanced capability is 0.125mm.

What is PTH?

PTH: Platted through Holes. The drilled hole on a PCB panel has completed a plating process to allow a copper connection with pads connected to the hole.


What is a Mixt raw material stack-up?

It’s a stack-up done with different raw materials. It’s mainly used for radiofrequency applications. Signal layers are done by FR4, and radiofrequency is done by a specific material. It helps to reduce the price of the PCB.

What is a controlled impedance and what type of impedance is it?

Electrical impedance is the measure of the opposition (resistance) that a circuit presents to the passage of a current when a voltage is applied in an alternating current circuit.

What is MassLam?

It’s the acronym for Mass Lamination. It defines that the inner layer is done by a least a double-side core bound to the external copper layer or core by PP.

What does PP stand for?

PP is the acronym for Prepreg. It’s a B-Stage material that is done of fiberglass saturated by epoxy resin (FR4). It’s used to bind the adjacent cores of a multi-layer PCB in a C-stage.

What is the maximum number of layers?

Commonly, the maximum number of layers is 36. However, some stack-up with 100 layers can be manufactured as samples. The minimum number of copper layers is 3.

What is a stack-up?

The stack-up defines the copper and dielectric layers of a PCB.

Any questions?

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