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Multilayer PCB Stackup Planning

In order to properly design the multi-layer printed circuit board, one should carefully consider the design of the layer stack-up. The need for planning the layer stack-up lies, on the one hand, on the technological capabilities of the production, and on another – on the requirements to the electrical properties of the printed circuit board. The latter include the impedance control, signals integrity, noise immunity and electromagnetic compatibility. Another important thing is the optimization of the layers stack-up and interconnections from the point of view of costs. Depending on the choice of the printed circuit board structure the production costs can vary significantly.

One need to remember that the multilayer PCB consists of a combination of cores, prepregs and copper foils. For your choice we have in stock a supply of materials. For their proper selection we recommend to use the table:

Standard copper thickness 9 μm
18 μm
35 μm
50 μm
70 μm

Types and thickness of prepregs 0,075 mm (1080)
0,105 mm (2116)
0,185 mm (7628)
0,216 mm (7628)

Standard core thickness 0,1 mm
0,13 mm
0,21 mm
0,25 mm
0,36 mm
0,51 mm
0,71 mm
1,0 mm
1,2 mm
1,6 mm
2,0 mm
2,4 (2,5) mm
3,2 mm


Below we put the most common designs of layers stack-up’s of printed circuit boards. The optimal ones (cheapest) we marked with the icon "Recommended".



4 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



6 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



8 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



10 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



PCB stackup



PCB stackup



12 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



PCB stackup



14 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



16 layer printed circuit board

PCB stackup



PCB stackup



PCB stackup



Universal PCB for prototyping

Prototype PCB

We have created a universal prototype printed circuit board for our clients to give them the possibility to check their ideas at the stage of designing new devices. This PCB contains universal solder pads and the most common types of connectors and commutation elements. The board is also equipped with four built-in power supplies - 1.8V, 3.3V, 5V and an adjustable voltage stabilizer. It is possible to mount a battery compartment that can contain two lithium-ion or alkaline-manganese elements) onto this board.

Our prototype board is also compatible with Raspberry PI 3 and Raspberry PI Zero computers. It also includes the necessary components and connections to mount the Arduino Nano module. It gives the possibility to design and check various types of electronic devices, including those connected to IoT.

Both types of assembling – SMD and THT can be used for this PCB. One- or double-sided assembly is also possible on this board.

Below you can see the specification of our prototype board, including link to the detailed technical information, including a scheme, description of the functionalities and other necessary practical information:

Specification:

  • 232 solder pads, including 88 dedicated for power/grounding
  • 4 types of stabilized voltage sources (with LED indication) on 1.8V, 3.3V, 5V and with regulated output voltage
  • compartment for two batteries
  • 3 USB connectors (type A, type B mini and micro)
  • connector for programming target systems in the ISP standard
  • a Raspberry PI connector
  • an Arduino Nano core
  • 2 tact buttons
  • 1 DIP switch with 8 positions
  • 6 LED’s for SMD mounting
  • 2 connectors (block terminal and DC jack) + switch for external power supply
  • 8 mounting holes (including 2 that can be used for attaching the battery compartment)

You can download User Manual here:

User Manual for Prototype PCB

Download User Manual in pdf

PCB surface finishing

To preserve the solderability of printed circuit boards for a considerable period of time, it is important to protect the copper surface of the soldering pads with a suitable coating or in other words, to provide a so-called surface finishing.

Surface finishing is made on soldering pads and other copper elements opened from solder mask. In modern productions, as a rule the several types of surface finishes with different properties are used.

For the appropriate selection of surface finishes and for their parameters specification there are a number of regulations, of which the most common are the following IPC standards:

  • J-STD-003 Solderability Tests for Printed Boards - defines the solderability test methods;

  • IPC 2221 Generic Standard on Printed Board Design - defines the basic requirements for the design of printed circuit boards;

  • IPC-7095A Design and Assembly Process Implementation for BGAs - focuses on the BGA components;

We offer a wide range of surface finishes to make an appropriate selection regarding the PCB project requirements.

  • HAL or HASL (Hot Air Leveling or Hot Air Solder Leveling) uses the tin-lead (Sn-Pb) alloys and the alignment by the hot air knife. This finishing is currently most commonly used due to its properties. It provides excellent solderability with substantial shelf life. HAL finishing is easy to manufacture and inexpensive. It is compatible with all methods of soldering or assembling - the manual soldering, wave soldering, reflow etc. The negative feature of this type of finishing is the presence of the lead - one of the most toxic metals that are prohibited for use on the territory of the European Union by the RoHS directive (Restriction of Hazardous Substances). Another limitation - it is surface non-uniformity that is not acceptable in case of fine pitch components. Besides it is not compatible with the COB technology (Chip on Board).


  • Lead free HASL finishing is similar to the normal HASL, except that it could comprise of different alloys like Sn100, Sn96,5/Ag3,5, SnCuNi, SnAgNi and does not contain lead. The finishing is fully RoHS compliant and meets  all the requirements of safety and solderability. However, due to the fact that finishing is applied at the considerably higher temperatures, more rigorous requirements are imposed on PCB base materials. Lead free HASL is compatible with all methods of soldering or assembling both in lead and lead free technologies, but it requires the appropriate temperature profiles during the soldering. As compared to SnPb HAL, it is more expensive due to the higher prices of alloys as well as higher energy consumption.


  • Immersion Gold or ENIG (Electroless Nickel/ Immersion Gold ) - the finishing from a Ni/Au family. The thickness of the finishing: Ni 3 – 5.0 µm, Au 0,06 – 0,1 µm. The finishing is made by chemical method. The main function of thin gold layer is to protect the nickel layer from oxidation, and the nickel layer prevents a mutual diffusion of gold and copper. The excellent flatness of the finishing makes it suitable to use in case of fine pitch components. The finishing is fully RoHS compliant. Compatible with all methods of soldering. The main limitation is a higher price. Besides there could be a risk of immersion gold defect due to the oxidation, so-called "black pad" that is critical for BGA assembly.


  • Gold Fingers - the finishing from a Ni/Au family. Plating thickness: Ni 5-9 µm, Au 0,2 - 1,0 µm. It is applied by electrochemical deposition (i.e. electroplating). Most often the finishing is used for PCB edge connectors. It has high mechanical strength, resistance to abrasion and adverse environmental effects. Indispensable where it is important to ensure excellent electrical contact with long service life.


  • Immersyjna tin - the finishing made chemically. It is compatible with all methods of soldering or assembling. The finishing has an acceptable shelf life period - up to one year. This is achieved by using organic compounds to make the barrier to intermetallic bonds that affect the oxidation of the surface. Such kind of insulating also prevents tin from crystallization. The finishing with the thickness of 1 µm has a good flatness and suitable for fine pitch components.


  • OSP (Organic Solderability Preservatives) - a family of organic coatings that applied directly onto the bare copper to protect it from oxidation during storage and soldering. This inexpensive finishing, has a  flat surface and is suitable for SMD assembly. It complies with the RoHS directive. As a result it is a cheap alternative to the HASL finishings.  Unfortunately, it has a limited shelf life (months) and quickly degrade during the soldering process.

Materials for printed circuit boards

The main elements of the PCB are dielectric substrate (rigid or flexible) with copper conductors on it, vias and holes both plated and non plated.

As the dielectric substrate the glass-epoxy laminates or composite materials are used. Basic types and parameters of materials used for the production of printed circuit boards are given in the table.

Type

Description

Glass transient temperature Tg

Dielectric constant Dk

Main suppliers

FR4

FR stands for Fire Retardant. FR4 is a glass fiber epoxy laminate. It is the most commonly used PCB material.

135°C

3,8-4,7

Shengyi, Isola, Nanaya, KB, Goldenmax

FR4 halogen free

This laminate type does not contain halogen, antimony, phosphorus, etc., does not emit hazardous substances when burning.

140°C

4,5 -4,9

Shengyi, Nanya

FR4 High Tg, FR5

These laminate types have excellent performance in Pb-free soldering.

170°C

3,8-4,6

Nanya, Nelco, Panasonic

RCC

RCC is electrolytic copper foil coated with a layer of special epoxy resin

130°C

4,0

SengYi, Nelco

PD

Polyimide resin with aramid basis

260°C

4,4

Arlon, Nelco

High frequency (PTFE)

High Frequency laminates are used in PCBs that require a low dissipation factor (Df) and very stable dielectric constant (Dk)

240–280°C

2,2–10,2

Taconic, Rogers

High frequency (non PTFE)

240–280°C

3,5

Rogers

Polyimide

Material for the production of flexible and rigid-flex PCB

195-220°C

3,4

Dupont, Taiflex


Most often printed circuit boards are made of standard glass-epoxy laminate namely FR4 type, with an operating temperature from -50 to + 110°C, glass transition temperature Tg of 135°C. The dielectric constant Dk can range from 3.8 to 4.6, depending on the supplier and type of material. For compliance with the lead-free technology assembly usually the laminates FR4 High Tg or FR5 are used. When there is a requirement of continuous operation at the high temperature or under extensive temperature stresses the polyimide as a base material is used. Besides polyimide has a good electric strength and often used in military products or in high endurance applications. For printed circuit boards for high frequency or microwave range the special materials are used. The cost of these materials is higher than the basic material FR4.

FR-4

The family of laminates under the name FR-4 by the NEMA (National Electrical Manufacturers Association, USA) classification. These are the most common materials for the single sided, double sided and multilayer printed circuit boards with strict requirements for mechanical strength. FR-4 is a composite material based on woven glass-epoxy compounds. As a rule, laminate has a matte yellow color, green color of the PCB gives it a solder mask which is applied to the surface. Flammability rating is UL94-V0.

Depending on the properties and applications, FR-4 laminates are divided into the following subclasses:

  • standard, with a glass transition temperature Tg of ~ 130°C, with UV blocking or without it. The most common and widely used type, at the same time, the cheapest of FR-4;

  • with a higher glass transition temperature, Tg ~ 170°C - 180°C, compatible with the lead free reflow technology;

  • halogen-free, compatible with the lead free reflow technology;

  • with normalized index of CTI ≥ 400, ≥ 600;

FR-1/FR-2

The family of laminates under the name FR-1 and FR-2  by the NEMA (National Electrical Manufacturers Association, USA) classification. These materials are made from paper and phenol compounds and are used only for the production of single side printed circuit boards. FR-1 and FR-2 has the similar parameters, the main difference is that FR-1 has a higher glass transition temperature Tg. Because of the similarity of the parameters and applications of FR-1 and FR-2, many of the material suppliers produce only one type of laminates, most often  FR-1. Laminates have a good ability to mechanical processing (milling, punching). Flammability rating is UL94-V0.

FR-1/FR-2 laminates are divided into the following subclasses:

  • standard;

  • halogen-free, without phosphorus and antimony, non-toxic;

  • with normalized index of CTI ≥ 400, ≥ 600;

  • non hydrophobic;

CEM-1

The family of laminates under the name CEM-1 by the NEMA (National Electrical Manufacturers Association, USA) classification. These materials are made from paper and two layers of woven glass epoxy and phenol compounds and are used only for the production of single sided printed circuit boards. As a rule, they have a milky white or milky yellow color. Laminates are incompatible with the process of metallization in holes, therefore, they are used only for the production of single sided printed circuit boards. Dielectric properties close to that of FR - 4, mechanical endurance is somewhat worse. CEM-1 is a good alternative to FR-4 when the price is the deciding factor. Flammability rating is UL94-V0.

CEM1 laminates are divided into the following subclasses:

  • standard;

  • with a higher Tg , compatible with the lead free reflow technology;

  • halogen-free, without phosphorus and antimony, non-toxic;

  • with normalized index of CTI ≥ 600;

  • non hydrophobic, with good dimension stability;

CEM-3

The family of laminates under the name CEM-3 by the NEMA (National Electrical Manufacturers Association, USA) classification. Composite material based on glass-epoxy compounds, usually has a milky white color. Very widely used in the production of double-sided PCBs with plated holes. The properties are very similar to that of FR-4, except the lower mechanical endurance. CEM-3 is a cheaper alternative to FR-4 for most applications. Laminates have a good ability to mechanical processing (milling, punching). Flammability rating is UL94-V0.

Depending on the properties and applications, CEM-3 laminates are divided into the following subclasses:

  • standard, with UV blocking or without it.

  • with a higher Tg , compatible with the lead free reflow technology;

  • halogen-free, without phosphorus and antimony, non-toxic;

  • with normalized index of CTI ≥ 600;

RO3000

A family of laminates developed for wide use in the early 90s of XX century. These materials have excellent electrical properties at the high frequencies and high thermal stability. The CTE (coefficient of thermal expansion) along the X and Y axes is close to the CTE of copper and FR4, therefore it is possible to produce the reliable RO3000 / FR4 hybrid PCBs. Low dielectric losses (Df = 0,0013 at a frequency of 10 GHz) provide great benefits when using these laminates in the applications for microwave range.

RO4000

This is a family of materials for a very high frequency range, which has been designed, on the one hand, to achieve the performance comparable with that of materials containing polytetrafluoroethylene (PTFE), and on the other hand, to simplify the technology of PCB production, that is, to make it more in line with the traditional technology used for reinforced laminates (FR4). Materials RO4000 contain reinforced fibreglass of a high glass transition temperature (Tg = 280 °C) with a thermosetting polymer as a bonding agent as well as additives ceramics.

Polyimide

Is a flexible polymeric film, the often used as the substrate for flexible printed circuit boards. The polyimide films produced under the trademarks Kapton, Rogers, Dupont. Advantages: excellent flexibility in the wide temperature range, good electrical properties, high chemical resistance (except for hot concentrated alkalies), very good tensile strength. Some types of polyimide have additional advantages (the coefficient of expansion in accordance with that of a copper, small internal stresses). Working temperatures from -200°C to + 300°C. Disadvantages: high water absorption (up to 3% by weight), relatively high price. Despite the high glass transition temperature (Tg ≥ 250 °C), their high temperature properties are limited by the bonding compound layers.

The polyimide film thickness can vary widely, but in practice most of the flexible materials are available with the thicknesses in a narrow range from 12 to 125 µm. When designing the flexible printed circuit boards it can be useful to remember the practical rule: the stiffness of the flexible materials is proportional to the third power of their thickness. That means if the material thickness is doubled, it becomes eight times tougher and with the same load will bend eight times less.

Production capabilities

An engineer must be proficient in the capabilities of the technological process based on which the board will be manufactured. Compliance with technological standards at the design phase of a printed circuit board ensures its subsequent high-quality and reliable production, enables high volumes to be produced by minimizing defects, and also ensures the reliable functioning of the devices where the PCB is used. The above allows to reduce cost on both the product introduction phase and its operational phase.

For your convenience, we put the most important technological parameters into the table:


Common parameters (single-, double- and multilayer printed circuit boards)

Value

Board thickness, mm

0,4-3,2

Copper thickness, μm

9, 18, 35, 70, 1051

Maximum PCB dimensions, mm

550,0 х 1150,0

Material

FR1, FR2, FR4, CEM1, CEM3, halogen free; with index of CTI ≥ 400, ≥600; for RF and microwave freq. range (Rogers, Arlon); high Tg materials – up to 175 0C; metal core and other. 2

PCB outline processing

routing, scoring (V-cut), punching

Surface finishing

HAL RoHS (Lead free), HAL SnPb, Immersion gold (ENIG), Immersion Tin, Gold Flash, Gold Fingers, carbone, OSP

Legend colour

white, black, yellow, green 3

Solder mask colour

green, white, black (glossy and matte), red, blue 3



Parameters

Typical

Advanced

Multilayer PCB

Number of layers

4-14

4-28

Minimum conductor width4, mm

0,1

0,076

Minimum conductors space4, mm

0,1

0,076

Minimum space between conductor and board’s outline (outer layers / inner layers), mm

0,5/0,5

0,3/0,5

Minimum hole size (mechanical drilling)6, mm

0,2

0,2

Aspect ratio

1:8

1:12

Minimum annular ring5, mm

0,15

0,127

Blind vias

yes

yes

Buried vias

yes

yes

Minimum solder mask swell, mm

0,05

0,05

Minimum solder mask bridge, mm

0,1

0,1

Legend width (silkscreen), mm

-

0,1

Minimum legend symbol height (silkscreen), mm

1,0

0,7

Multilayer HDI PCB

Number of layers

4-16

4-28

Build-up

3-N-3

4-N-4

Minimum conductor width4, mm

0,1

0,076

Minimum conductors space4 (outer layers / inner layers), mm

0,1/0,076

0,076/0,064

Minimum space between conductor and board’s outline (outer layers / inner layers), mm

0,5/0,5

0,3/0,5

Minimum hole size (laser drilling), mm

0,1

0,075

Minimum annular ring5 (outer layers / inner layers), mm

0,15/0,1

0,127/0,1

Via-in-pad technology

yes

yes

Stacked and staggered micro vias

yes

yes

Copper plugged vias

yes

yes

Resin plugged vias

yes

yes

Minimum solder mask swell, mm

0,05

0,025

Minimum solder mask bridge, mm

0,1

0,1

Double sided PCB

Minimum conductor width4, mm

0,15

0,1

Minimum conductors space4, mm

0,15

0,1

Minimum space between conductor and board’s outline, mm

0,5

0,3

Minimum hole size, mm

0,3

0,2

Aspect ratio

1:8

1:12

Minimum annular ring5, mm

0,2

0,15

Minimum solder mask swell, mm

0,1

0,05

Minimum solder mask bridge, mm

0,15

0,1

Legend width (silkscreen), mm

-

0,1

Minimum legend symbol height (silkscreen), mm

1,0

0,7

Single sided PCB

Minimum conductor width4, mm

0,2

0,15

Minimum conductors space4, mm

0,2

0,15

Minimum space between conductor and board’s outline, mm

0,5

0,3

Minimum hole size, mm

0,5

0,4

Minimum annular ring5, mm

0,3

0,2

Minimum solder mask swell, mm

0,1

0,05

Minimum solder mask bridge, mm

0,2

0,1

Legend width (silkscreen), mm

-

0,1

Minimum legend symbol height (silkscreen), mm

1,5

1,0

Flex PCB

Number of layers

1-6

Material

Polyimide, PET

Minimum conductor width4, mm

0,15

0,1

Minimum conductors space4, mm

0,15

0,1

Minimum space between conductor and board’s outline, mm

0,5

0,25

Minimum hole size, mm

0,3

0,2

Coverlay swell (coverlay to soldering pad gap), mm

0,2

0,1

Aluminum core PCB

Number of layers

1-2

1-4

Board thickness, mm

0,5-3,2

Copper thickness, μm

35

Dielectric thickness, μm

50, 75, 100, 150

Thermal conductivity, W/mK

0,7-4

Breakdown voltage, kV

2-12

Maksimum PCB dimensions, mm

550,0 х 950,0

Material

AL 5052

Minimum conductor width4, mm

0,2

0,15

Minimum conductors space4, mm

0,2

0,15

Minimum space between conductor and board’s outline, mm

0,5

0,25

Minimal hole size, mm

0,9

0,6

Minimum solder mask swell, mm

0,15

0,05


1 It is possible to make thicker copper on demand.
2 Other materials on demand.
3 Other colours on demand.
4 For copper thickness 9 μm and 18 μm.
5 (Pad size – hole size)/2
6 It is possble to use laser drilling on demand.



Minimum clearances for different cooper thicknesses

Finished copper thickness, μm 35 70 105 140 210
Minimum Trace, mm 0,1 0,20 0,23 0,30 0,60
Minimum clearance, mm 0,1 0,20 0,24 0,35 0,70

Finished copper thickness, μm 35 70 105 140 210
Minimum Trace, mm 0,1 0,20 0,27 0,34 0,60
Minimum clearance, mm 0,1 0,20 0,30 0,45 0,85
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