What's the difference between FPC rolled copper and electrolytic copper?

The difference between calendering and electrolysis in FPC copper cladding process:


The difference between manufacturing methods


1, Gao Chundu is rolling copper (>99.98%) copper by rolling method in FPC - because adhesive has excellent FPC and copper foil, copper foil adhesive strength and high working temperature, can be no bubble dip in 260 DEG C in molten tin.


2, CuSO4 electrolyte can continuously manufacture a layer of "copper foil", so easy to control thickness, the longer the time, the thicker the copper foil! In general, the thickness of copper foil in the factory has strict requirements, generally between 0.3mil and 3mil, there is a dedicated copper thickness tester to test its quality. Control the thickness of the copper foil is mainly based on two reasons: one is the uniform copper foil can have very uniform temperature coefficient of resistance, low dielectric constant, which can make the signal transmission loss is smaller, and the capacitance of different capacitance requirements of high dielectric constant, so as to accommodate higher capacity in a finite volume why, the resistance capacitance than smaller, after all is a high dielectric constant!


Secondly, the thin copper foil under the condition of large current temperature rise is small, which is of great benefit to the heat dissipation and component life. The copper wire width in the digital integrated circuit is best less than 0.3cm is also the reason. The finished FPC board is very uniform and soft in color (because the surface brush resists flux).


For a FPC substrate wrapped with copper foil, how can we put the components on it to realize the signal conduction between components, not the whole board? The copper wire twisted around the plate is used to transmit the electrical signals. Therefore, we only need to remove the unnecessary parts of copper foil and leave the copper wire parts.


How to achieve this step, first of all, we need to understand a concept, that is "negative line" or "line of film", we will film with lithography printed board circuit design, and then put a photosensitive ingredient of specific spectral sensitive and chemical reaction of dry film covered on the substrate on the dry film two, photopolymerization type and light decomposition type, light photopolymerization type dry film in specific spectral will from hardening, water soluble substances into water insoluble and light decomposition type is just the opposite.


Here we use the photopolymer photosensitive dry film first covered on the substrate, and then covered with a line of film to expose it, the exposure of black opaque, and vice versa is transparent (line part). The light passes through the film to the photosensitive dry film. What's the result? Any film transparent light local dry film dark colors began to harden the surface of the substrate, tightly wrapped in foil, like the circuit diagram printed on the substrate, then we passed the development step (using sodium carbonate solution from Non Hardened dry film), may not need dry film protection of copper foil exposed, this is called stripping (Stripping) process. Next we use copper etching liquid (chemical corrosion of copper) for etching substrate, no dry film protection hardened dry film under copper The whole army was wiped out., so the circuit diagram on the substrate show. The whole process is called "image transfer", and it occupies a very important position in the PCB manufacturing process.


The difference between quality and use


1, electrolytic copper as its name implies is through the electrolytic method to make copper ions adsorbed on the substrate and form copper foil, so it is characterized by: strong conductivity, but the bending resistance is relatively weak.


2, rolled copper is obtained by extrusion method copper foil, it is characterized by: bending resistance is good, but the conductivity is weaker than electrolytic copper, mainly used in flip phone camera, and so on. In appearance, the electrolytic copper is red and the rolled copper is yellow.


 

(Source: internal information)

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