Our company produces printed circuit boards from high-quality imported materials, ranging from standard FR4 to microwave materials and polyimide. In this section we define the basic terms and concepts used in the field of design and manufacturing printed circuit boards. The section tells about completely simple things, familiar to every design engineer. However, there are a number of nuances here that many developers do not always take into account.

*** Additional information available,

Multilayer PCB Design
Let's consider a typical design of a multilayer board (Fig. 1). In the first, most common, option, the internal layers of the board are formed from double-sided copper-laminated fiberglass, which is called the “core”. The outer layers are made of copper foil, pressed with the inner layers using a binder - a resinous material called "prepreg". After pressing at high temperatures, a “pie” of a multilayer printed circuit board is formed, in which holes are then drilled and metallized. The second option is less common, when the outer layers are formed from “cores” held together with prepreg. This is a simplified description; there are many other designs based on these options. However, the basic principle is that prepreg acts as the bonding material between the layers. Obviously, there cannot be a situation where two double-sided "cores" are adjacent without a prepreg spacer, but a foil-prepreg-foil-prepreg...etc structure is possible, and is often used in boards with complex combinations of blind and hidden holes.

Blind and hidden holes
The term "blind holes" refers to vias that connect the outer layer to the nearest inner layers and do not have access to a second outer layer. It comes from English word blind, and is similar to the term "blind holes". Hidden, or buried (from English buried), holes are made in the inner layers and have no exit to the outside. The simplest options for blind and hidden holes are shown in Fig. 2. Their use is justified in the case of very dense wiring or for boards very saturated with planar components on both sides. The presence of these holes leads to an increase in the cost of the board from one and a half to several times, but in many cases, especially when routing microcircuits in BGA package with small steps, you can’t do without them. Eat various ways formation of such vias, they are discussed in more detail in the section, but for now we will consider in more detail the materials from which the multilayer board is constructed.

Tg—glass transition temperature (structure destruction)
Dk - dielectric constant

Basic dielectrics for printed circuit boards
The main types and parameters of materials used for the manufacture of MPPs are given in Table 1. Typical designs of printed circuit boards are based on the use of standard fiberglass laminate type FR4, with an operating temperature, usually from -50 to +110 °C, glass transition (destruction) temperature Tg about 135 °C. Its dielectric constant Dk can be from 3.8 to 4.5, depending on the supplier and type of material. For increased requirements for heat resistance or when mounting boards in an oven using lead-free technology (t up to 260 °C), high-temperature FR4 High Tg or FR5 is used. When required to work permanently high temperatures or when sharp changes temperatures polyimide is used. In addition, polyimide is used for the manufacture of high-reliability circuit boards, for military applications, and also in cases where increased electrical strength is required. For boards with microwave circuits (more than 2 GHz), separate layers of microwave material are used, or the entire board is made of microwave material (Fig. 3). Most famous suppliers special materials- Rogers, Arlon, Taconic, Dupont companies. The cost of these materials is higher than FR4 and is roughly shown in the last column of Table 1 relative to the cost of FR4. Examples of boards with different types dielectrics are shown in Fig. 4, 5.

Material thickness
Knowing the available material thicknesses is important for an engineer not only for determining the overall thickness of the board. When designing MPP, developers are faced with the following tasks:
- calculation of the wave resistance of conductors on the board;
- calculation of the value of interlayer high-voltage insulation;
- selection of the structure of blind and hidden holes.
Available options and thicknesses various materials are given in tables 2-6. It should be taken into account that the tolerance on the thickness of the material is usually up to ±10%, therefore the tolerance on the thickness of the finished multilayer board cannot be less than ±10%.

Table 2. Double-sided FR4 “cores” for the internal layers of the printed circuit board

Typically in stock;
h - On request (not always available)
m - Can be manufactured;
Note: to ensure the reliability of the finished boards, it is important to know that for foreign internal layers we prefer to use cores with 35 micron foil rather than 18 micron (even with a conductor and gap width of 0.1 mm). This increases the reliability of printed circuit boards.
The dielectric constant FR4 cores can range from 3.8 to 4.4 depending on the brand.

Table 3. Prepreg (“bonding” layer) for multilayer printed circuit boards

The dielectric constant of FR4 prepreg can range from 3.8 to 4.4 depending on the brand.
Please check this parameter for a specific material with our engineers by email

Table 4. Rogers microwave materials for printed circuit boards

* Dk - dielectric constant

Table 5. Arlon microwave materials for MPP

Note: Microwave materials are not always in stock, and their delivery time can take up to 1 month. When choosing a board design, you need to check the stock status of the MPP manufacturer.

Dk — Dielectric constant
Tg—glass transition temperature

I would like to note the importance of the following points:
1. In principle, all FR4 core values ​​from 0.1 to 1.0mm are available in 0.1mm increments. However, when designing urgent orders, you should check in advance the availability of materials in the warehouse of the PCB manufacturer.
2. When it comes to the thickness of the material - the materials intended for manufacturing double-sided boards, material thickness is indicated including copper. The “core” thicknesses for the internal layers of the MPP are specified in the documentation without the copper thickness.
Example 1: material FR4, 1.6/35/35 has a dielectric thickness: 1.6-(2x35 µm)=1.53 mm (with a tolerance of ±10%).
Example 2: FR4 core, 0.2/35/35 has dielectric thickness: 200 µm (with tolerance ±10%) and total thickness: 200 µm+(2x35 µm)=270 µm.
3. Ensuring reliability. The permissible number of adjacent layers of prepreg in MPP is no less than 2 and no more than 4. The possibility of using a single layer of prepreg between the “cores” depends on the nature of the pattern and the thickness of the adjacent copper layers. The thicker the copper and the richer the pattern of the conductors, the more difficult it is to fill the space between the conductors with resin. And the reliability of the board depends on the quality of the filling.
Example: copper 17 microns - you can use 1 layer 1080, 2116 or 106; copper 35 microns - you can use 1 layer only for 2116.

PCB pad coatings
Let's look at what types of coatings there are for copper pads. Most often, sites are coated with a tin-lead alloy, or PIC. The method of applying and leveling the surface of solder is called HAL or HASL (from English Hot Air Solder Leveling - leveling solder with hot air). This coating provides the best solderability of the pads. However, it is being replaced by more modern coatings, as a rule, compatible with the requirements of the international RoHS directive. This directive requires the prohibition of the presence harmful substances, including lead, in products. So far, RoHS does not apply to the territory of our country, but it is useful to remember its existence. The problems associated with RoHS will be described in one of the subsequent sections, but for now let's take a look at possible options coverage of MPP sites in Table 7. HASL is applied everywhere, unless there are other requirements. Immersion (chemical) gold plating is used to provide a smoother board surface (this is especially important for BGA pads), but has slightly lower solderability. Soldering in a furnace is performed using approximately the same technology as HASL, but hand soldering requires the use of special fluxes. Organic coating, or OSP, protects the copper surface from oxidation. Its disadvantage is the short shelf life of solderability (less than 6 months). Immersion tin provides flat surface and good solderability, although it also has a limited shelf life for soldering. Lead-free HAL has the same properties as lead-containing HAL, but the composition of the solder is approximately 99.8% tin and 0.2% additives. The contacts of the blade connectors, which are subject to friction during operation of the board, are electroplated with a thicker and more rigid layer of gold. For both types of gilding, a nickel underlayer is used to prevent diffusion of gold.

Table 7. PCB pad coatings

Note: All coatings except HASL are RoHS compliant and suitable for lead-free soldering.

Protective and other types of printed circuit board coatings
To complete the picture, consider functional purpose and PCB coating materials.
- Solder mask - applied to the surface of the board to protect conductors from accidental short circuits and dirt, as well as to protect fiberglass laminate from thermal shock during soldering. The mask does not carry any other functional load and cannot serve as protection against moisture, mold, breakdown, etc. (except when used special types masks).
- Marking - applied to the board with paint over the mask to simplify identification of the board itself and the components located on it.
- Peelable mask - applied to specified areas of the board that need to be temporarily protected, for example, from soldering. It is easy to remove in the future, since it is a rubber-like compound and simply peels off.
- Carbon contact coating - applied to certain areas of the board as contact fields for keyboards. The coating has good conductivity, does not oxidize and is wear-resistant.
- Graphite resistive elements - can be applied to the surface of the board to perform the function of resistors. Unfortunately, the accuracy of the denominations is low - no more accurate than ±20% (with laser adjustment - up to 5%).
- Silver contact jumpers - can be applied as additional conductors, creating another conductive layer when there is not enough space for routing. Mainly used for single-layer and double-sided printed circuit boards.

Table 8. PCB Surface Coatings

Conclusion
The choice of materials is great, but, unfortunately, often when producing small and medium-sized series of printed circuit boards, the stumbling block becomes the availability necessary materials in the warehouse of the plant - manufacturer of MPP. Therefore, before designing an MPP, especially if we are talking about creating a non-standard design and using non-standard materials, it is necessary to agree with the manufacturer on the materials and layer thicknesses used in the MPP, and perhaps order these materials in advance.

Our company produces printed circuit boards from high-quality domestic and imported materials, ranging from standard FR4 to FAF microwave materials.

Typical designs printed circuit boards are based on the use of standard fiberglass laminate type FR4, with an operating temperature from -50 to +110 °C, and a glass transition temperature Tg (softening) of about 135 °C.

For increased requirements for heat resistance or when mounting boards in an oven using lead-free technology (t up to 260 °C), high-temperature FR4 High Tg or FR5 is used.

Basic materials for printed circuit boards:

"+" - Typically in stock

"+/-" - On request (not always available)

Prepreg ("tie" layer) for multilayer printed circuit boards

FR-4

Foil-coated fiberglass with nominal thickness 1.6 mm, lined with copper foil 35 microns thick on one or both sides. Standard FR-4 is 1.6 mm thick and consists of eight layers (“prepregs”) of fiberglass. The central layer usually contains the manufacturer's logo; its color reflects the flammability class of this material (red - UL94-VO, blue - UL94-HB). Typically, FR-4 is transparent, the standard green color is determined by the color solder mask, applied to the finished printed circuit board

• volumetric electrical resistance after conditioning and restoration (Ohm x m): 9.2 x 1013;
• surface electrical resistance (Ohm): 1.4 x1012;
• peeling strength of foil after exposure to galvanic solution (N/mm): 2.2;
• flammability (vertical test method): class Vо.

MI 1222

is a layered pressed material based on fiberglass impregnated with an epoxy binder, lined on one or both sides with copper electrolytic foil.

• surface electrical resistance (Ohm): 7 x 1011;
• specific volumetric electrical resistance (Ohm): 1 x 1012;
• dielectric constant (Ohm x m): 4.8;
• foil peel strength (N/mm): 1.8.

FAF-4D

They are glass fiber reinforced fluoroplastic, lined on both sides with copper foil. Application: - as bases printed circuit boards operating in the microwave range; - electrical insulation for printed elements of receiving and transmitting equipment; - capable of long-term operation in the temperature range from +60 to +250° C.

• Adhesion strength of foil to base per 10 mm strip, N (kgf), not less than 17.6(1.8)
• Tangent of the angle dielectric losses at a frequency of 106 Hz, no more than 7 x 10-4
• Dielectric constant at frequency 1 MHz 2.5 ± 0.1
• Available sheet sizes, mm ( maximum deviation along the width and length of the sheet 10 mm.) 500x500

T111

material made from a thermally conductive polymer based on ceramics with an aluminum base, are used in cases where it is intended to use components that emit significant thermal power(for example, ultra-bright LEDs, laser emitters, etc.). The main properties of the material are excellent heat dissipation and increased dielectric strength when exposed to high voltages:

• Aluminum base thickness - 1.5 mm
• Dielectric thickness - 100 microns
• Copper foil thickness - 35 microns
• Thermal conductivity of the dielectric - 2.2 W/mK
• Dielectric thermal resistance - 0.7°C/W
• Thermal conductivity of aluminum substrate (5052 - analogue of AMg2.5) - 138 W/mK
• Breakdown voltage - 3 KV
• Glass transition temperature (Tg) - 130
• Volume resistance - 108 MΩ×cm
• Surface resistance - 106 MΩ
• Highest operating voltage (CTI) - 600V

Protective solder masks used in the production of printed circuit boards

Solder mask (also known as brilliant green) - layer durable material, designed to protect conductors from ingress of solder and flux during soldering, as well as from overheating. The mask covers the conductors and leaves the pads and blade connectors exposed. The method of applying a solder mask is similar to applying photoresist - using a photomask with a pattern of pads, the mask material applied to the PCB is illuminated and polymerized, the areas with soldering pads are unexposed and the mask is washed off from them after development. Most often, the solder mask is applied to the copper layer. Therefore, before its formation protective layer the tin is removed - otherwise the tin under the mask will swell from the heating of the board during soldering.

PSR-4000 H85

Green color, liquid photosensitive heat-hardening, 15-30 microns thick, TAIYO INK (Japan).

Has approval for use by the following organizations and end product manufacturers: NASA, IBM, Compaq, Lucent, Apple, AT&T, General Electric, Honeywell, General Motors, Ford, Daimler-Chrysler, Motorola, Intel, Micron, Ericsson, Thomson, Visteon, Alcatel , Sony, ABB, Nokia, Bosch, Epson, Airbus, Philips, Siemens, HP, Samsung, LG, NEC, Matsushita(Panasonic), Toshiba, Fujitsu, Mitsubishi, Hitachi, Toyota, Honda, Nissan and many, many others;

IMAGECURE XV-501

Colored (red, black, blue, white), liquid two-component solder mask, Coates Electrografics Ltd (England), thickness 15-30 microns;

DUNAMASK KM

Dry film mask from DUNACHEM (Germany), thickness 75 microns, provides tenting of vias and has high adhesion.

To make the base of a printed circuit board, foil and non-foil dielectrics are used - getinax, fiberglass, fluoroplastic, polystyrene, ceramic and metal (with a surface insulating layer) materials.

Foil materials- These are multilayer pressed plastics made of electrically insulating paper or fiberglass impregnated with artificial resin. They are covered on one or both sides with electrolytic foil with a thickness of 18; 35 and 50 microns.

Foil-coated fiberglass laminate of the SF grade is produced in sheets with dimensions of 400×600 mm and a sheet thickness of up to 1 mm and 600×700 mm with a larger sheet thickness; it is recommended for boards that are operated at temperatures up to 120°C.

Higher physical and mechanical properties and heat resistance are provided by fiberglass laminates of SFPN grades.

The dielectric slofodite has a copper foil 5 microns thick, which is obtained by evaporating copper in a vacuum.

For multilayer and flexible boards use heat-resistant fiberglass laminates of the STF and FTS brands; they are operated in the temperature range from minus 60 to plus 150°C.

Non-foil STEF dielectric is metallized with a layer of copper during the manufacturing process of a printed circuit board.

The foil is made from high-purity copper, the impurity content does not exceed 0.05%. Copper has high electrical conductivity and is relatively resistant to corrosion, although it requires protective coating.

For printed circuit assembly the permissible current value is selected: for foil 100–250 A/mm2, for galvanic copper 60–100 A/mm2.

For the production of printed cables, reinforced fluoroplastic foil films are used.

Ceramic boards can operate in the temperature range of 20...700ºС. They are made from mineral raw materials (for example, quartz sand) by pressing, injection molding or film casting.

Metal boards used in products with high current load.

Aluminum or alloys of iron and nickel are used as a base. An insulating layer on the surface of aluminum is obtained by anodic oxidation with a thickness of tens to hundreds of micrometers and an insulation resistance of 109–1010 Ohms.

The thickness of the conductor is 18; 35 and 50 microns. Based on the density of the conductive pattern, printed circuit boards are divided into five classes:

– the first class is characterized by the lowest density of the conductive pattern and the width of the conductor and spaces more than 0.75 mm;

- fifth grade has highest density pattern and the width of the conductor and spaces within 0.1 mm.

Since the printed conductor has a low mass, the force of its adhesion to the base is sufficient to withstand alternating mechanical overloads acting on the conductor up to 40 q in the frequency range 4–200Hz.

Standards for printed circuit board materials are presented below in the corresponding section “Standardization of Printed Circuit Board Manufacturing”.

The quality of supplied materials complies with the IPC4101B standard, and the manufacturers' quality management system is confirmed by international certificates ISO 9001:2000.

FR4 – fiberglass laminate with fire resistance class 94V-0 is the most common material for the production of printed circuit boards. Our company supplies the following types materials for the production of single- and double-sided printed circuit boards:

• Fiberglass laminate FR4 with a glass transition temperature of 135ºС, 140ºС and 170ºС for the production of single-sided and double-sided printed circuit boards. Thickness 0.5 - 3.0 mm with foil 12, 18, 35, 70, 105 microns.
• Basic FR4 for internal layers of MPP with glass transition temperatures of 135ºС, 140ºС and 170ºС
• FR4 prepregs with glass transition temperatures of 135ºС, 140ºС and 170ºС for pressing MPP
• Materials XPC, FR1, FR2, CEM-1, CEM-3, HA-50
• Materials for boards with controlled heat dissipation:
  • (aluminum, copper, stainless steel) with a dielectric with thermal conductivity from 1 W/m*K to 3 W/m*K produced by Totking and Zhejiang Huazheng New Material Co.
  • Material HA-30 CEM-3 with thermal conductivity 1 W/m*K for the production of single- and double-sided printed circuit boards.

For some purposes, a high-quality non-foil dielectric is required that has all the advantages of FR4 (good dielectric properties, stability of characteristics and dimensions, high resistance to adverse influences). climatic conditions). For these applications we can offer non-foil FR4 fiberglass laminate.

In many cases where fairly simple printed circuit boards are required (in the production of household equipment, various sensors, some components for automobiles, etc.), the excellent properties of fiberglass are redundant, and indicators of manufacturability and cost come to the fore. Here we can offer the following materials:

• XPC, FR1, FR2 - foil getinaks (base made of cellulose paper impregnated with phenolic resin), widely used in the manufacture of printed circuit boards for consumer electronics, audio and video equipment, in the automotive industry (arranged in ascending order of properties, and, accordingly, price ). Excellent stamping.
• CEM-1 is a laminate based on a composition of cellulose paper and fiberglass with epoxy resin. Stamps beautifully.

Our assortment also includes electrodeposited copper foil for pressing MPP produced by Kingboard. Foil is supplied in rolls of various widths, foil thicknesses are 12, 18, 35, 70, 105 microns, foil thicknesses of 18 and 35 microns are almost always available from our warehouse in Russia.

All materials are produced in accordance with the RoHS directive, the content of harmful substances is confirmed by relevant certificates and RoHS test reports. Also, all materials, many items have certificates, etc.

Laminate FR4

You can find a detailed description of the laminate.

Laminates in TePro warehouse

Microwave material ROGERS

NOTE: To use ROGERS material in the production of circuit boards, please indicate this in the order form

Since Rogers material is significantly more expensive than standard FR4, we are forced to introduce an additional markup for boards manufactured using Rogers material. Working fields of used workpieces: 170 × 130; 270 × 180; 370 × 280; 570 × 380.

Metal based laminates

Visual representation of the material

Aluminum laminate ACCL 1060-1 with dielectric thermal conductivity 1 W/(m K)

Description

Aluminum laminate CS-AL88-AD2(AD5) with dielectric thermal conductivity 2(5) W/(m K)

Description

Prepreg

In production we use prepregs 2116, 7628 and 1080 grade A (highest) from ILM.

You can find a detailed description of prepregs.

Solder mask

Properties

You can find a detailed description of the solder mask.

Frequently asked questions and answers on laminates and prepregs

What is XPC?

What's the difference between FR1 and FR2?

What is FR2?

What is FR3?

What is FR4?

What is FR5?

What is CEM-1?

What is CEM-3?

What is G10?

How can laminates be replaced?

What are "prepregs"?

What does FR or CEM stand for?

Is FR4 really green?

Does the color of the logo mean anything?

Does logo orientation mean anything?

What is UV blocking laminate?

What laminates are suitable for plating through holes?

Is there an alternative for plating through holes?

What is "material thickness"?

What is: PF-CP-Cu? IEC-249? GFN?

What is CTI?

What does #7628 mean? What other numbers are there?

What is 94V-0, 94V-1, 94-HB?