Understanding double layer PCB

Understanding double layer PCB

PCB (Printed Circuit Board) is a tiny electronic circuit board that can be achieved in mass production at a minimum cost. PCB  can be categorized according to a number of layers such as a single layer PCB, double layer PCB, or multilayer PCB.

Table of Contents

What is double layer PCB?

Double layer PCB is a two-layer PCB consists of two conductive layers. Also, known as a double-sided. Unlike a single layer PCB, the insulating layer of material is in the middle of the board and both sides can be soldered. Double-sided PCB comes with two-sided traces as top and bottom layers. In the manner of physical features, double-layer PCB is thicker than a single-layer PCB due to the vast dielectric layer.

double layer PCB

What is the advantage of double layer PCB?

By incorporating more layers on a single PCB, cause to increase flexibility and functionality. Double layer PCBs’ cost is low comparatively and the complexity of the circuit is less than multilayer PCBs. It minimizes the difficulty of the PCB layout  by providing the facility of layout on both sides.

Also, Double layer PCBs allow a huge density of components. One layer can use to add components or add extra connections.The manufacturing process of double-layer PCBs results in high quality and reliable compare to single-layer PCBs.

What uses a double sided PCB?

HVAC systems

Heating, ventilation, and air conditioning (HVAC) systems that provide heating and cooling for residential and mercantile buildings use double-side PCB.

Power supplies and regulators

There are voltage regulators PCBs which are designed to gain constant output voltage.

Converters ups power systems

A UPS PCB is designed to provide emergency power to a device in the event of a power outage. When the main power or input power source fails, it supplies the load with the required AC voltage inverted from storage batteries.

Printers, phone systems

Nowadays, researchers are rapidly developing new ways to make phones smaller and faster. Due to the increase in capabilities of PCBs, mobile phones have gotten smaller in size and more powerful.

How does double layer PCB work?

A double layer PCB works by having a digital or analog electrical signal that routes between the layers. And the rigid dielectric layer prevents the two layers from signal interfering. Both the top layer and bottom layer are copper layers. The solder mask layer is a thin layer that covers the exposed copper layer of the board. And, it protects the copper from corrosion and oxidation.
double layer PCB stack up

How do I know how many layers a PCB has?

To make Double layer PCB following things are needed.

  • Copper-clad board
  • Laser Printer
  • Glossy paper
  • Permanent marker pen
  • Ferric Chloride (FeCl3 )
  • Sandpaper
  • Designing PCB layout

As the first step, design a schematic diagram in the EDA tool (PCB Design Software). Then convert schematic into a PCB layout and do the routing.

  • Trim the copper board

PCB manufacturing starts with the preparation of the copper clad board.

  • Toner transfer method

Mainly two methods are used for manufacturing double layer PCB through-hole and surface mounts. Commonly use the method that drills holes into the board in the manufacturing process. Use the toner transfer method to make the PCB. Usually, the PCB layout was exported as printed.

Then get a mirror print out of the top layer and bottom layer of the PCB layout separately using a laser printer.

Firstly printed image of the bottom layer is transferred to the board from the glossy paper by ironing it. Make sure that the board is aligned correctly with the printed layout. Using the reference of the circuit image printed on glossy paper first draw a basic sketch on a copper plate by a permanent black marker.

After ironing, place the printed plate in warm water for around 10-15 minutes. The paper will dissolve gently and remove the Paper. Then drill the holes which are needed in the bottom layer. The same procedure will be done for the top layer.

  • Etching process

During the etching process, the Fecl3 reacts with the unmasked copper and removes the unwanted copper from the PCB. Check whether after every 2-3 minutes all copper is etched or not. Rinse carefully. Dry it by using a clean cloth. Trim to final size and refine edges with sandpaper.

  • Applying solder mask

The next step is to apply a solder mask. It will protect the exposed copper and prevent the solder from shorting between the traces.

  • Drilling process

The final step is to drill holes and solder all the components. Then double layer PCB is ready.

designing PCB layout

What is the difference between single layer and double layer PCB?

what is the difference between single layer and double layer PCB
difference between single layer and double layer PCB

How do I know how many layers a PCB has?

Based on practical experience, the number of PCB layers can be determined by traces and components of a PCB board used for a certain industry. This is not a precise way. Even though upgrading the hardware is so fast, there are few designers who have the ability to rebuild the design rules. 

Also, it is an easy way to see if a board has inner layers by using a bright light. Even if it doesn’t have blind vias choose a place on the board where there aren’t traces and see if you can see light through it. If it’s blocked in some places, that’s probably copper. Even without that, most multi-layer PCBs have used the standard green Liquid Photo Imageable (LPI) solder mask which is darker in appearance than double layer.

Also, we can determine the initial number of layers according to their usage. Usually, single and double layers PCBs are simple prototyped ones. Four layer PCBs are also simple boards used for some microcontroller boards and baseboards.

Not for CPU boards with memory interface. Six layer PCBs are large boards that are used for high density circuits. Eight and ten layer PCBs are used for the SODIMM computer on module. Twelve layer PCBs are heavy industry boards with many tracks use for industrial PC designs.

Based on the use of the via hole technology in the circuit connection of the multilayer circuit board is also able to determine the number of PCB layers, by identifying the vias which are used to connect couples of inner layers. This method is easy to use but also limited.

The number of PCB layers depends on pin density. As indicated by the below chart we can identify the number of layers.

identify the number of layers
layers of a PCB

How many PCB layers are on a motherboard?

A motherboard is a PCB that contains the principal components of a computer or other device. Today’s motherboards usually use either 6 or 8 layers. And if it requires more power to run, more layers will be added as power planes to connect and power them.

How many layers is an iphone PCB?

PCBs are the heart of the iPhone, holding the A-series chip, RAM, flash storage, radio chip, etc. They represent around half the value of the iPhone. Modern phones normally use 10 layers of the PCB. And stacked SLP usually needs 20. This provides for a maximum density of components on a given surface. The iPhone X had also been tipped to have an eight-layer RF board, a 10-layer AP board, and two layers of interposers.

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