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pcb_manufacturing [2026/05/27 14:03] – [11. outer layer etching] sophiepcb_manufacturing [2026/05/29 12:31] (current) – [15. surface finish] sophie
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 # Manufacturing processes of multilayer Printed Circuit Boards (PCB) # Manufacturing processes of multilayer Printed Circuit Boards (PCB)
  
-This page is dedicated to explaining the process flow of multilayer PCB manufacturing. The image bellow gives an overview of this flow [(https://www.ncabgroup.com/wp-content/uploads/2015/10/02-NCAB_Group_Seminars_How-to-make-a-PCB_2_0_150925.pdf)]. It is important to note that this flow is adapted depending on the type of PCB (single sided, double sided, or multilayer). +This page aims to explain the manufacturing process flow of multilayer PCB manufacturing. {{ref>fig_manuf_flow}} gives an overview of this flow. It is important to note that this flow is adapted depending on the type of PCB (single sided, double sided, or multilayer). 
  
- unpopulated 
  
-<figure center|fig_label>+<figure center|fig_manuf_flow>
 {{ ::capture_d_ecran_2026-05-20_134249.png?direct&800|}} {{ ::capture_d_ecran_2026-05-20_134249.png?direct&800|}}
-<caption>Manufacturing flow of a multilayer unpopulated PCB</caption>+<caption>Manufacturing flow of unpopulated multilayer PCBs [(https://www.ncabgroup.com/wp-content/uploads/2015/10/02-NCAB_Group_Seminars_How-to-make-a-PCB_2_0_150925.pdf)]</caption>
 </figure> </figure>
  
 - -
-## 0. substrate/board fabrication 
- 
-TBA  
-FR4 CCL  
- 
------------------------------------ 
-\\ 
  
 ## 1. board cutting ## 1. board cutting
  
-The board (copper clade laminate sheet) is cut and its edges are soften. +The board is cut and its edges are soften. 
  
----------------------------------------+-------------------------------------- 
 +-
 ## 2. inner layer printing and etching  ## 2. inner layer printing and etching 
 +
 ** 2.1 pre-treating ** ** 2.1 pre-treating **
  
-During this step the CCL (cooper clade laminate) sheet is cleaned to **remove any impurities** and to **roughned** (slighlty) its surface. The roughneing of the surface is important to ensure a **good adhesion** of the photosensitive film that will be applyied during the next process step. **Chemicals (acidic solution)** are used for the surface roughening. Once the roughening is done, the board is **dryed** to stop envenly the roughening process. +During this step the CCL (cooper clade laminate) sheet is cleaned to remove any impurities and to roughned (slighlty) its surface. The roughneing of the surface is important to ensure a good adhesion of the photosensitive film that will be applyied during the next process step. Chemicals (acidic solution) are used for the surface roughening. Once the roughening is done, the board is dryed to stop envenly the roughening process. 
  
  
 ** 2.2. dry photosensitive film lamination ** ** 2.2. dry photosensitive film lamination **
  
-Once the surface is prepared, a **photosensitive film** is applyied onto the panel. This is done through a **lamination** machine that laminates a liquid photoresist stucked inbetween **two PET and a PE films**. The lamination is usually processed in a **cleanroom environment** (controlled atmosphere and temperature). +Once the surface is prepared, a photosensitive film is applyied onto the panel. This is done through a lamination machine that laminates a liquid photoresist stucked inbetween two PET and a PE films. The lamination is usually processed in a cleanroom environment (controlled atmosphere and temperature). 
  
 ** 2.3. UV ray exposure ** ** 2.3. UV ray exposure **
  
-During this step the circuit **design is transfered** onto the photosensitive film. There are two methods to do so:  +During this step the circuit design is transfered onto the photosensitive film. There are two methods to do so:  
-  * exposing all the photosentive film through a **mask** that has the wanted circuit design, +  * exposing all the photosentive film through a mask that has the wanted circuit design, 
-  * by **laser direct imaging**: the lasers exposes the photosensitive film by drawing the desired pattern that maches the wanted circuitry (no mask is needed). +  * by laser direct imaging: the lasers exposes the photosensitive film by drawing the desired pattern that maches the wanted circuitry (no mask is needed). 
 The panel is now constituted of the CCL sheet on top of which the photosensitive film is polymerised on some areas (the exposed areas), and not polymerised in other areas.   The panel is now constituted of the CCL sheet on top of which the photosensitive film is polymerised on some areas (the exposed areas), and not polymerised in other areas.  
-\\ +
 ** 2.4. developpment ** ** 2.4. developpment **
  
-In previous steps, specific parts of the resist film have been polimerized through UV light exposure. In this step, the **unwanted part of the film (unexposed)** will be removed to reveal the copper. It could be either an additive (the exposed part is removed) or a negative (unexposed areas are removed) development. Negative development is the most common method. +In previous steps, specific parts of the resist film have been polimerized through UV light exposure. In this step, the unwanted part of the film (unexposed) will be removed to reveal the copper. It could be either an additive (the exposed part is removed) or a negative (unexposed areas are removed) development. Negative development is the most common method. 
  
  
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 ** 2.5. etching ** ** 2.5. etching **
  
-Now that the unwanted copper parts are exposed, it is **etched** away using **amonia or chloride based etchants**. The polimerized film is unsensitive to this etching and stays in place to protect some area of panel. +Now that the unwanted copper parts are exposed, it is etched away using amonia or chloride based etchants. The polimerized film is unsensitive to this etching and stays in place to protect some area of panel. 
  
 ** 2.6. stripping ** ** 2.6. stripping **
  
-In the previous step the unwanted copper has been removed. However the wanted copper is still covered by the polemirized film. This step is focused on **removing this resist** film by chemically stripping it away. Then, the panel with the desired copper pattern is cleaned to remove remaining stripping chemicals. +In the previous step the unwanted copper has been removed. However the wanted copper is still covered by the polemirized film. This step is focused on removing this resist film by chemically stripping it away. Then, the panel with the desired copper pattern is cleaned to remove remaining stripping chemicals. 
  
  
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 ------------------------------------- -------------------------------------
- 
  
 ## 10. plating ## 10. plating
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 -------------------------------------- --------------------------------------
-\ +
-\ +
-cc+
  
 ## 11. outer layer etching ## 11. outer layer etching
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 ## 15. surface finish  ## 15. surface finish 
  
-The surface finish can either be ENIG (most common) or tin immersion (often chosen for applications using press fit pins). +The surface finish can either be ENIG, tin immersion, or HASL. The ENIG surface finish is the most common one and tin immersion is often chosen for applications using press fit pins. 
  
 **Electroless Nickel and Immersion Gold (ENIG) ** **Electroless Nickel and Immersion Gold (ENIG) **
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 <figure center|legend> <figure center|legend>
 {{ :capture_d_ecran_2026-05-21_142815.png?direct |}} {{ :capture_d_ecran_2026-05-21_142815.png?direct |}}
-<caption> Nickel and gold depositions on the panel coated with solder mask by the ENIG process </caption>+<caption> Nickel and gold depositions on the panel which is already coated with solder mask by the ENIG process </caption>
 </figure> </figure>
  
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 This type of surface finish is quite common as the surface is made of a material similar to the one used to solder the components. The first step is to clean to surface. Then, the panel is put into a molted solder bath (with a controlled content of copper): the solder attach itself to copper (which are the areas where solder is needed – other copper areas are covered by the solder mask). Then hot air is blowed onto the surface to remove any excess of solder. The PCB is then cleaned to remove any remaining solder solution.  This type of surface finish is quite common as the surface is made of a material similar to the one used to solder the components. The first step is to clean to surface. Then, the panel is put into a molted solder bath (with a controlled content of copper): the solder attach itself to copper (which are the areas where solder is needed – other copper areas are covered by the solder mask). Then hot air is blowed onto the surface to remove any excess of solder. The PCB is then cleaned to remove any remaining solder solution. 
  
----------------------------------------+-------------------------------------- 
 +-
 ## 16. profile ## 16. profile
  
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 ## 17. tests and inspection ## 17. tests and inspection
  
-**electrical test**+**17.1. electrical test**
  
 This step is important to check if the circuit has the right connexions: we are looking for any unexpected short- or open-circuit that would translate a wrong functioning of the PCB. Two method exists to do so: the flying probe test (suitable for smaller volumes and prototypes: each electrical net is tested individually) and the bed of nail or fixture machine (suitable for large batches: all electrical nets are tested simultaneously). The 4-wire kelvin test can also be conducted, in addition of the previous one to check net continuity and resistance.  This step is important to check if the circuit has the right connexions: we are looking for any unexpected short- or open-circuit that would translate a wrong functioning of the PCB. Two method exists to do so: the flying probe test (suitable for smaller volumes and prototypes: each electrical net is tested individually) and the bed of nail or fixture machine (suitable for large batches: all electrical nets are tested simultaneously). The 4-wire kelvin test can also be conducted, in addition of the previous one to check net continuity and resistance. 
  
-** final inspection**+** 17.2. final inspection**
  
 Then each PCB must be inspected to check that there are no remaining defaults in their functioning. Visual checking and and a wide range of other tests are performed to identify any remaining damage on the board.  Then each PCB must be inspected to check that there are no remaining defaults in their functioning. Visual checking and and a wide range of other tests are performed to identify any remaining damage on the board. 
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 -------------------------------- --------------------------------
  
- +[comment]: <> (
-n +
-## Input & outputs during the manufacturing processes (to remove from this page, and to be added later in the LCI page) +
  
  
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 |  activation  |  immersing the surface in catalyst colloid to attach it to the surface sites  |  |  | |  activation  |  immersing the surface in catalyst colloid to attach it to the surface sites  |  |  |
  
 +)
  
 ## References ## References
  
 ~~REFNOTES~~ ~~REFNOTES~~