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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

- 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

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.

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

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.

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

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

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.

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.

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.

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

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

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

The minimum PTH free of solder mask is 0.45mm.

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

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

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

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

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.

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.

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.

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

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

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.

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.

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.

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

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.

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.

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.

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.

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

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.

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.

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

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

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.

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.