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pcb_manufacturing [2026/06/05 16:17] – [7. Plating (optional)] mariepcb_manufacturing [2026/06/05 23:52] (current) – [2. Inner layer printing and etching] sophie
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 ** 2.4. Developpment ** ** 2.4. Developpment **
  
-In previous steps, specific parts of the resist film have been polymerized 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 polymerized through UV light exposure. In this step, the unwanted part of the film will be removed to reveal the copper. The development process can be described as either positive (the exposed resin is dissolved by the chemical developer) or negative (the unexposed resin is dissolved by the chemical developer). In PCB manufacturing, the negative development process is predominantly used. 
  
  
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 ## 8. Back-drilling (optional) ## 8. Back-drilling (optional)
  
-The back-drilling consist of removing parts of the plating of holes for signal integrity.+The back-drilling consists of removing parts of the holes plating for signal integrity.
  
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 **9.1. Image transfer** **9.1. Image transfer**
  
-This step is focused on transferring the outer layer pattern on the board to deliver the functionality of the device. The same method as for the inner layer imaging is used (photosensitive film, mask, and UV light). However, in the inner layers the exposed parts were the electrical pattern (the pattern is protected during the following steps)) whereas in the outer layer all the surface of the panel is exposed except for the electrical pattern (in the next step additional copper will be added only on the electrical pattern).  Two methods can be used: laser direct imaging (no mask needed), outworks or film and exposing them to UV light. It is crucial to be in a clean room environment because the exposition is very sensitive to any atmosphere change. +This step is focused on transferring the outer layer pattern on the board to deliver the functionality of the device. The same method as for the inner layer imaging is used (photosensitive film, mask, and UV light). However, in the inner layer imaging process, the exposed parts were the electrical pattern (the pattern is protected during the following steps), whereas in the outer layer all the surface of the panel is exposed except for the electrical pattern (in the next step additional copper will be added only on the electrical pattern).  Two methods can be used: laser direct imaging (no mask needed), outworks or film and exposing them to UV light. It is crucial to be in a clean room environment because the exposition is very sensitive to any atmosphere change. 
  
 **9.2. Development**  **9.2. Development** 
  
-Then the unwanted photoresist is taken out during the developing step, just like the inner layer developing step. The panel is immerged in a chemical solution that reacts with the unexposed the photoresist. The panel is then rinsed to remove any remaining solution composed of chemicals and dissolved photoresist. +Then the unwanted photoresist is taken out during the developing step, just like the inner layer developing step. The panel is immersed in a chemical solution that reacts with the unexposed photoresist. The panel is then rinsed to remove any remaining solution composed of chemicals and dissolved photoresist. 
  
 <figure center blank|fig_label> <figure center blank|fig_label>
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 ## 10. Plating ## 10. Plating
  
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 ** 10.2. Tin deposition ** ** 10.2. Tin deposition **
  
-Then, to protect the copper in the next process steps a thin tin layer is deposited with the same pattern, here again using the electroplating process (the chemical solution differs from the one used for copper deposition). +Then, to protect the copper in the next process steps, a thin tin layer is deposited with the same pattern, again using the electroplating process, but with a chemical solution different from the one used for copper deposition. 
  
 <figure center blank|fig_label> <figure center blank|fig_label>
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 ## 11. Outer layer etching ## 11. Outer layer etching
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 **11.1. Stripping** **11.1. Stripping**
  
-In this process all the remaining photoresist is removed from the panel, outlining the final tin-protected copper design. The resist is chemically removed putting the panel in a chemical solution. +In this process, all the remaining photoresist is removed from the panel, outlining the final tin-protected copper design. The photoresist is chemically removed putting the panel in the stripping solution. 
  
  
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 ## 12. Optical inspection ## 12. Optical inspection
  
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 ## 13. Solder mask  ## 13. Solder mask 
  
-The solder mask is added to protect the metal from oxidation and the pattern from being deteriorated. +The solder mask is added to protect the metal from oxidation and the pattern from being deteriorated in the long term. 
  
  
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 The surface is covered to protect areas that needs it (connection of components do not need protection) to prevent oxidations and provide insulation.  The surface is covered to protect areas that needs it (connection of components do not need protection) to prevent oxidations and provide insulation. 
-First, the surface is pumiced (mechanical brushing or chemical etching) to roughened the surface to promote adhesion of the solder mask. The panel is then rinsed and dried to prevent copper corrosion. Then the liquid solder mask is applied on bottom and top surfaces using the stray-coating or a silk screen (one side and then the panel is flipped to conduct the same process on the other side). The solder mask is then hardened by during the pre-cure process so that it stays in place in an even layer. +First, the surface is pumiced (mechanical brushing or chemical etching) to roughened the surface to promote adhesion of the solder mask. The panel is then rinsed and dried to prevent copper corrosion. Then the liquid solder mask is applied on bottom and top surfaces using the stray-coating or a silk screen (one side and then the panel is flipped to conduct the same process on the other side). The solder mask is then hardened during the pre-cure process so that it stays in place, forming an even layer. 
  
 **13.3. Solder mask exposure** **13.3. Solder mask exposure**
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 ## 14. Legend ## 14. Legend
  
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 ## 15. Surface finish  ## 15. Surface finish 
  
-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. +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.  This step is important because it allows customers to add components to the PCBs and prevents copper oxidation.
  
 **Electroless Nickel and Immersion Gold (ENIG) ** **Electroless Nickel and Immersion Gold (ENIG) **
  
-This step is important because it allows customers to add components to the PCBs and prevents copper oxidation. This process is very complexes.  +The ENIG process is very complex.  
-First, the panel goes into a series of chemical bath (a first one – “activator” – to clean and prepare the surface for nickel deposition, the second is an electroless nickel bath, the third one is a immersion gold bath)+The panel goes into a series of chemical baths: a first one, an “activator”, to clean and prepare the surface for nickel deposition, a second, which consists of an electroless nickel bath, and one being an immersion gold bath.
 Gold is applied in a very thin layer (less than 1µm) to protect the nickel from oxidation.  Gold is applied in a very thin layer (less than 1µm) to protect the nickel from oxidation. 
  
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 ** Tin immersion ** ** Tin immersion **
  
-First, the panel undergoes a UV exposure to fully cure the solder mask (if not tin can interact with it), then an acid solution is poured on the surface to clean it and roughened it and chemicals are rinsed out with water. Tin is applied in a very thin layer forming a bond with copper. Then, the PCB is cleaned in warm water and dried. This surface finish is more afordable compared to the ENIG process. +First, the panel undergoes a UV exposure to fully cure the solder mask (if not, tin can interact with it), then an acid solution is poured on the surface to clean it and roughened it and chemicals are rinsed out with water. Tin is applied in a very thin layer forming a bond with copper. Then, the PCB is cleaned in warm water and dried. This surface finish is more afordable compared to the ENIG process. 
  
  
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 **V-socre** **V-socre**
  
-Rotating blade on the upper and lower part of the panel creating a “V-shape” pattern where we want the separation of two PCB to be. The depth of the V-shaped lines is closely controlled. +Rotating blade on the upper and lower part of the panel creating a “V-shape” pattern where we want the separation of two PCB to be. The depth of the V-shaped lines is closely controlled. The separation itself will be performed later in the supply chain.
  
 ** Routing** ** Routing**
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 **17.1. 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 connections: we are looking for any unexpected short- or open-circuit that would translate to 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.
  
 ** 17.2. 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 a wide range of other tests are performed to identify any remaining defect on the board. 
  
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