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PCB manufacturing process

PCB manufacturing process

Let’s look at how printed circuit boards are made, for example, on the fourth floor.

Manufacturing process of four-layer PCB board:
1.Chemical Clean
In order to get a good quality etching pattern, it is necessary to ensure that the corrosion resistant layer firmly combines with the surface of the substrate, requiring that the substrate surface is free of oxidation layer, oil, dust, fingermark and other contaminants.Therefore, before coating the anti-corrosion layer, the surface of the plate should be cleaned and the surface of the copper foil should reach a certain degree of coarsening layer.

Inner plate: start making four layers, and the inner layer (the second and third layers) must be made first.The inner panel is a copper sheet made of glass fiber and epoxy resin composite on the upper and lower surfaces.

  1. Cut Sheet Dry Film Lamination
    Photoresist: in order to make the desired shape of the inner panel, we first paste dry film (photoresist, photoresist) on the inner panel.Dry film is made up of polyester book film, photoresist film and polyethylene protective film.When laminating, first remove the polyethylene protective film from the dry film, and then paste the dry film on the copper surface under heating and pressure.

  1. Image Expose and Image Develop
    Exposure: under the irradiation of ultraviolet light, the light initiator absorbed the light energy into free radicals, free radicals to trigger a light polymerization monomer polymerization crosslinking reaction, reaction after the formation of insoluble in dilute alkali solution of polymer structure.Polymerization reaction to last for a period of time, in order to guarantee the stability of the process, don’t immediately after exposure to tear to polyester film, should stay more than 15 minutes, with the polymerization continues, enhancement before tearing to polyester film.  

Development: the active group in the unexposed part of the photosensitive film reacts with dilute alkali solution to produce soluble substances and dissolves, leaving the image part that has been photosensitive cross-linked and cured.

4.Copper Etch
In the process of production of flexible printed circuit board or printed circuit board, with chemical reaction method to remove, not part of the copper foil needed for the formation of circuit graphics, photoresist is at the bottom of the copper is not affected by the etching are preserved.

5.【 Strip Resist】 【Post Etch Punch】 【AOI Inspection】 【Oxide】
The purpose of film removal is to remove the corrosion resistant layer on the etched plate surface to expose the copper foil below.The filtration of “membrane slag” and the recovery of waste liquid shall be properly handled.If the rinsing after the film removal can be completely clean, you can consider not to do pickling.After cleaning, the board should be completely dry to avoid water retention.

 6.Layup with prepreg
Prepreg – epoxy resin impregnated glass fiber is required in addition to the oxidized inner layer.The function of lamination is to stack the sheet covered with protective film in a certain order and place it between two layers of steel plate.

7.Layup with copper foil  Vacuum Lamination Press
Copper foil – to present the inner plate on both sides are covered with a layer of copper foil again, then to multilayer pressure (in a fixed period of time need to measure temperature and pressure of extrusion) after cooling to room temperature, the rest is a multilayer board together.

  1. CNC Drill
    Under the precise condition of inner layer, nc drilling is conducted according to the mode.High precision drilling is required to ensure that the hole is in the correct position.

  1. Electroless Copper
    Copper must be filled in the hole in order for the through-hole to pass between layers (metallize the non-conductive resin and glass fiber bundles on the wall of the hole).The first step is to coat the hole with a thin layer of copper, which is completely a chemical reaction.The final thickness of the copper plating was one millionth of an inch in 50 inches. 
  2. Cut Sheet Dry Film Lamination
    Photoresist: we once applied photoresist to the outer layer.
  3. 【Image Expose】 【Image Develop】
    Outer exposure and development
  1. Copper Pattern Electro Plating
    This also became a second copper plating, the main purpose is to thicken line copper and through hole copper thickness.

13.Tin Pattern Electro Plating

Its main purpose is to etch inhibitors that protect the copper conductors it covers from attack when alkaline copper is corroded (protecting all copper wires and the inside of the through-hole).

14.Strip Resist
We already know the purpose, just chemically, the copper on the surface is exposed.

15.Copper Etch
We know the purpose of etching, and the tin part protects the copper foil below.

  1. 【LPI coating side 1】 【Tack Dry】 【LPI coating side 2】【Tack Dry】
    【Image Expose】【Image Develop】 【Thermal Cure Soldermask】
    The resistance layer, which is used to expose the welding disc, is usually called the green oil layer. In fact, it is to dig holes in the green oil layer and expose the welding disc and other places that do not need the green oil cover.Proper cleaning will yield the right surface features.

17.Surface finish
> HASL, Silver, OSP, ENIG
> Tab Gold if any

Hot air leveling solder coating HAL (commonly known as spray tin) process is to dip on the PCB soldering flux on first, then dip coating in the molten solder, and then through between two pieces of air knife, knife in the wind hot compressed air blow off the excess solder on the PCB and eliminate excess solder metal hole at the same time, to get a bright, smooth, uniform solder coating.

Purpose of the gold finger design is by the connector connector plug as plate export foreign contact, therefore need to gold finger process. Chose gold because of its excellent electric conductivity and oxidation resistance. But because the cost of gold is very high so only applies to the gold finger, local or chemical gold plating

> Image Develop

> Copper Etch

> Strip Resist

> Post Etch Punch

> AOI Inspection AOI
> Oxide

> Layup

> Vacuum Lamination Press

2) CNC Drilling
> CNC Drilling

3) Outer Layer
> Deburr
> Etch back – Desmear
> Electroless Copper
> Cut Sheet Dry Film Lamination
> Image Expose
> Image Develop

4) Plating
> Image Develop
> Copper Pattern Electro Plating
> Tin Pattern Electro Plating
> Strip Resist

> Copper Etch
> Strip Tin

5) Solder Mask
> Surface prep
> LPI coating side 1
> Tack Dry
> LPI coating side 2
> Tack Dry
> Image Expose
> Image Develop
> Thermal Cure Soldermask

6) Surface finish
> HASL, Silver, OSP, ENIG
> Tab Gold if any
> Legend

7) Profile
> NC Routing or punch

8) ET Testing, continuity and isolation

9) QC Inspection
>  Ionics
> 100% Visual Inspection
> Audit Sample Mechanical Inspection
> Pack & Shipping