Printed Circuit Boards (PCB)

A Printed Circuit Board (PCB) or Printed Wiring Boards (PWB) consists of a superposition of alternating conductive and insulating layers. The ensemble forms a set of conductive, used for routing power and signal in electronic components. A PCB with electronics components mounted on it can be called a Printed Circuit Board Assembly (PCBA).

PCBs are used to interconnect components soldered on top of the electronic circuit. It distributes both signal and power to assembled components like CPUs, SSDs, RAM slots… Printed Circuit Board are contained in the vast majority of today electronic devices, from PCs to wearables passing by cars, to name a few.

We can categorize bare PCBs according to 3 criteria: the number of layers it is made of, its structure which is either rigid, flexible or a mix of bother, and its specificity according to the component it will be integrated it. Each of those categories are detailed in the following parts, as well as the high-level impact each category has on manufacturing process and material composition.

Number of Layers

The number of layers refers to the number of repetition of conductive traces layers. The layers are interconnected one to another via copper traces. The more layer with similar density will enable more possibility of interconnections between components. It induces 3 categories of PCBs, each having its own impact on the manufacturing process and field of application:

• Single-sided PCB: only one side of the board contains a conductive trace. Thus, the manufacturing process is the shortest as it requires only on traces printing and plating and does not require any alignment with other layer traces. As there is only one trace, it cannot interconnect many component and is thus used for very simple application like toys or basic calculators.
• Double-sided PCB: the two sides of the board contain a conductive trace. Thus, alignment of drills needs to be performed as well as trhough-hole plating to ensure inteconnections between the two sides of the PCB. This type of PCB is more common for power supplies, HVAC controllers or more complex IoT devices.
• Multilayer PCB: The board contains several layers of conductive traces above 2. It implies to superimpose serveral layers of insulating layers.The manufacturing is more complex. It requires the repetition of pattern printing and plating on each inner layer, which are then laminated together, before following the same manufacturing steps as in lower-layer count PCBs. The number of layer requires a high accuracy alignement of layer before driling to ensure inter-layer interconnections. This type of PCBs can account for diverse level of complexity, and are the one used in most electronic devices, like computers, medical equipment, TVs, etc.

The more layer, the more substrate, insulating material and copper traces.

Sources:

• https://www.nextpcb.com/blog/types-of-pcb
• https://www.mclpcb.com/blog/pcb-manufacturing-process/

PCB structure

The structure of the PCBs aims at distinguishing the requirements in terms of shape of the of PCBs depending in which product it is aimed to be integrated.

• Rigid: A rigid structure is the most classical shape of a PCB. It is composed of rigid and robustmaterial, usualy FR-4 material. It is compatible with both assembly technology. It is the most common structure and present in components like computers, medical equipements.
• Flex: It is composed of flexible plastic film like polyimide or PET. It adapts to many equipment shapes, it is light and resistant to vibration. It is particularly present in wearables.
• Rigid-flex: The structure is a mix between rigid PCBs boads and flexible interconnection between them. It combines the advantages of rigid PCBs while adapting to compact components. It requires complex lamination step to combine both PCB structures.

Source: https://www.nextpcb.com/blog/types-of-pcb

PCB specialization

The specialization of the PCBs refers to categories of PCBs with a specific need, thus requiring specific properties.

• High temperature: It is the type of PCB required when the component is exposed to very high temperatures or is assembled with high temperature technologies. The substrate is made of specific high glass transition temperature that remain stable under high temperature.
• Heavy copper: this PCBs contains contains a high thickness of copper. It is used for application where current is high to avoid voltage drops, overheating and limit current loss. It is selected for power converters, power distribution or battery management systems.
• High frequency: it is used for application where a high frequency of interconnection is required and thus must ensure signal integrity and minimize signal loss and distortion. The substrates are made of hydrocarbon ceramics or modified epoxies in this case. It is used for high-frequency systems like 5G/6G antennas, radar systems or communication system of satellites.
• Metal core: This kind of PCB contains a metal core, in addition to copper traces. The metal core, often made of aluminium, helps to dissipate heat for component with high power like LEDs or power transistors.
• High Density Interconnect (HDI): The high-density interconnect PCBs aim at concentrate a high density of interconnections between several components. It is possible via burried vias and micro-vias, in addition to through-hole vias. The drills are performed using laser drillers. It is mainly used for compact devices, smarthones and high-end equipment (servers…).
• Substrate-like PCB: This kind of PCBs embeds even more dense interconnections with very thin traces than HDI PCBs. Its manufacturing process is highly inspired from IC industry. It requires semi-additive process for plating steps and UV laser direct imaging technology to maintain very thin interconnections. This is particularly useful for high-perfomance components with a high compactivity like high-end smartphones.
• Standard PCB: The standard PCB structure made of FR4 substrate.

Source:

• https://www.nextpcb.com/blog/types-of-pcb
• https://www.pcbdirectory.com/community/what-are-substrate-like-pcbs

Assembly technologies

Once the bare PCB is manufactured, elements to be interconnected needs to be assembled on top of it. Among the elements that populates PCBs, we can find CPU sockets, RAM slots, but also capacitors, resitances… The PCB can be populated according to two technologies:

• Through-Hole Technology (THT). It consists in having leads passing through previously drilled holes, that are soldered on pads present on the opposite side of the PCB. This is an old technology, but still used for some power electronics.
• Surface-Mount Technology (SMT). The components are directly soldered on pads, without requiring through holes. It is the technology used for most digital equipment.

The assembly technology do not influence drastically the manufacturing process of bare PCB. It can sometimes influence the choice of substrate when it implies high temperatures.

Source: https://asselems.com/en/what-is-the-assembly-of-a-pcb

N/A

The system is composed of one main part, the board itself, composed itself of a succession of layers of substrate, insulating material and copper traces. When the PCB has a rigid-flex structure, we can consider that it is composed of a set of rigid PCB board, connected via a set of flexible PCB board.

This study aims at providing the cradle-to-gate environmental impact:

• Rigid bare PCBs.
• Standard PCB specialization.
• With either 2 or multiple layers.

This study exludes:

• All electronics devices assembled on the bare PCB.
• R&D activities to develop the PCB.
• The transition of the boards between manufacturing stages, which can be either manual or automated.
• The input copper clad laminate process impact.
• The end-of-production line multiple tests.

The functional unit of this study is “manufacture one squared-meter of rigid standard bare PCB”.

The reference flows are:

• The surface of substrate
• The surface of copper foil
• The weight of platted metal, both copper and surface finish ones

⇒ Goal: Define state of the art on life cycle stages to be considered.

⇒ Goal: List the technical information needed for the LCI.

• Raw materials
  • FR-4 = glass-reinforced epoxy laminate material (epoxy resin + glass fiber)
  • copper
• Chemicals
  • potassium carbonate
  • dicyanoaurate
  • sodium hydroxide

⇒ Goal: List the technical information needed for the LCI.

For each system sub-part:

• Manufacturing processes of PCB

⇒ Goal: List the technical information needed for the LCI.

⇒ Goal: List the technical information needed for the LCI.

⇒ Goal: List the technical information needed for the LCI.

⇒ Goal: Define state of the art on environmental impacts.

Taking the Econinvent dataset and documentation and Hischier R. et al. 2007 of the “printed wiring board production, for surface mounting, Pb free surface”. The dataset is baseb on a 1.6 mm thick 6-layer PWB with a mixture of several Pb-free surface finishing methods and a weight of a weight of 3.26 kg/m².

For 1m², using PEF3.1 and Simapro. Electricity consumption is the main contributor to GWP.

Gold, copper and electricity consumption are the main contributors to the single score.

• Processes
  • PCB factory
• Energy use
  • Electricity

Data needed from manufacturer :

• production volume
• line capacity
• installed power
• water usage

Impactful parameters :

• Technology: Through-Hole Technology (THT) or Surface Mount Technology (SMT)
• Substrate material: FR4 (mostly used), bio-based material, etc.
• Number of layers (1 to 16 generally)
• Surface (m2) → yield
• Type of surface finish

* About the Ecoinvent PWB dataset : Time and technological representativeness of this dataset is probably very low as it is sourced from AT&S AG (2006), US EPA (2000) and ZVEI (2006). PCB technologies as well as manufacturing technologies might have change or been optimized since then. As electricity consumption is a key contributor to environmental impact, there is a need for up-to-date electricity intensity of PCB production. Electricity location is an important factor, providing datasets with the most common location (China, South Est Asia, EU, USA, …?), though it is currently possible to copy the dataset and adapt the electricity mix of if the location is known. Considering finish separately As the amount of gold in the PCB is a key contributor to environmental impact, there is a need for precise gold quantity in PCB for an accurate LCA. Also, for PCBs without a gold finish there is an important “hidden burden” by using this dataset, though it is possible to copy the dataset and subtract the gold if needed. I propose to create separate datasets for the most common type of finish, instead of the actual arbitrary finishes mix.

⇒ Goal: Source every data we cited previously

⇒ Goal: List challenges and clarify priority areas for action