Electrochemical Copper-Free Process:
The main purpose of the preprocessing step:
1. To ensure the continuous integrity of the electroless copper deposition layer.
2. Ensure the bonding force between chemical copper and base copper foil.
3. Ensure the bonding force between chemical copper and inner copper foil.
4. Guarantee the bonding force between the electroless copper layer and the non-conductive substrate. The above is a brief description of the effect of chemical copper/electroless copper pretreatment.
The typical pretreatment steps of electroless copper are briefly described below:
The purpose of degreasing:
1. Remove the oil and grease in the copper foil and the hole.
2. Remove the copper foil and the dirt in the hole.
3. Helps to remove contamination and subsequent heat treatment from the copper foil surface.
4. Simple treatment of polymer resin fouling in drilling.
5. Remove the burr copper powder adsorbed in the hole produced by the bad drilling.
6. Oil removal adjustment. In some pretreatment lines, it is the first step in the treatment of composite substrates (including copper foil and non-conductive substrates).
The oil removal agent is generally alkaline, and some neutral and acidic raw materials are also used. Mainly in some atypical degreasing processes. Degreasing is a key bath fluid in the pretreatment line. Contaminated areas can cause problems with chemical copper coverage (ie, the generation of microvoids and copper-free areas) due to insufficient activator adsorption. Microvoids are covered or bridged by subsequent copper electroplating, but where there is no bond between the electroplated copper layer and the non-conductive substrate at the base, the end result may result in hole wall detachment and hole blowing. The internal coating stress generated by the electroplating layer deposited on the chemical copper layer and the vapor expansion force generated by the subsequent heating (baking, tin spraying, welding, etc.) Pulling away from the non-conductive substrate of the hole wall may cause the hole wall to detach. Also, the copper powder generated by the burr in the hole is adsorbed in the hole during the degreasing process, and also there is no bonding force between the copper layer and the non-conductive substrate, which may eventually lead to the detachment of the hole wall.
Whether the above two results occur or not, it is undeniable that the bonding force there is significantly worse and the thermal stress is significantly increased, which may destroy the continuity of the electroplating layer, especially in the welding or wave soldering process, resulting in the generation of blow holes. The hole blowing phenomenon is actually caused by the thermal expansion of the steam generated from the non-conductive substrate under the weak bonding force! If our electroless copper is deposited on the dirt on the base copper foil or on the contamination on the inner copper foil ring of the multilayer board, the bonding force between the electroless copper and the base copper will also be stronger than that of the well cleaned copper. The bonding force between the foils is very poor, and the result of poor bonding may occur. If the oil stain is spot-like, it may cause the occurrence of blistering. If the stain area is large, it may even cause the electroless copper to detach.
Important factors in the degreasing process:
1. How to choose the right degreaser – types of cleaning/degreasers
2. The working temperature of the degreaser
3. Concentration of degreaser
4. Immersion time of degreaser
5. Mechanical stirring in the degreasing tank
6. The cleaning point where the cleaning effect of the degreaser decreases
7. Washing effect after degreasing
In the above cleaning operations, temperature is a key factor to be concerned about. Many degreasing agents have a minimum temperature lower limit, below which the cleaning and degreasing effect drops sharply!
Influencing factors of washing:
1. Washing temperature should be above 60F
2. Air agitation
3. It is best to have a spray
4. The entire wash has enough fresh water to be replaced in time
In a sense, the water washing after the degreasing tank is as important as the degreasing. The degreaser remaining on the board surface and hole wall will also become a pollutant on the PCB circuit board, which will then contaminate other subsequent main treatment solutions such as micro-etching and activation. Generally, the most typical washings in this place are as follows:
a. The water temperature is above 60F
b. Air stirring
c. When the nozzle is equipped in the tank, the board is washed with fresh water to wash the board surface
Condition c is not often used, but a b two are necessary.
The water flow rate of cleaning water depends on the following factors:
1. The amount of waste liquid carried out (ml/hang)
2. The load capacity of the working plate in the washing tank
3. Number of washing tanks (countercurrent rinsing)
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