To drill the dirt and pitting
is just after the flexible printed circuit board nc drilling, chemical plating
of copper or copper plating directly in front of an important working
procedure, just flexible printed circuit board to achieve reliable electrical
interconnection, just flexible printed circuit board must be combined with its
special materials, polyimide materials for its main body and the
characteristics of acrylic acid is not resistant to strong alkali, choose
suitable to drill and pitting.There are two kinds of technology of defouling
and pitting technology of rigid flexible printed circuit board: wet method and
dry method.
The wet drilling and defouling
and pitting technology of rigid flexible printed circuit board consists of the
following three steps:
1. Swelling (also called
swelling treatment).The surface area that can be oxidized can be increased by
softening the pore wall substrate with alcohol ether bentonite, which can be
easily oxidized. Generally, butylcarbiol is used to make the pore wall
substrate dissolve and expand.
2. Oxidation.The purpose is to
clean the hole wall and adjust the charge of the hole wall.
(1) concentrated sulfuric acid
method: because concentrated sulfuric acid has strong oxidation and water
absorption, most of the resin can be carbonized and form water-soluble alkyl
sulfonates to be removed. The reaction formula is as follows:
CmH2nOn+H2SO4--mC+nH2O perforated wall resin drilling pollution effect is
related to concentration of concentrated sulfuric acid, treatment time and
solution temperature.The concentration of concentrated sulfuric acid used for
the removal of drilling dirt shall not be less than 86% and 20-40 seconds at
room temperature.Concentrated sulfuric acid only works on resin, but is not
effective for glass fiber. After concentrated sulfuric acid is used to concave
the hole wall, there will be glass fiber head protruding, which needs to be
treated with fluoride (such as ammonium fluoride or hydrofluoric acid).When
using fluoride to treat prominent glass fiber heads, technological conditions
should also be controlled to prevent core absorption due to excessive corrosion
of glass fiber. The general process is as follows:
- H2SO4:10%
NH4HF2:5-10 g/l
Temperature 30 ℃ in time: 3 to 5 minutes
According to this method of
punch after just - flexible printed circuit board to drill the dirt and
pitting, and then the hole metallization, through metallographic analysis,
found the inner drilling sewage didn't go to complete, lead to low copper layer
and hole wall adhesion, thermal stress experiment in metallographic analysis
for this (288 ℃, 10 +
1 second), the hole wall copper layer falls off and cause the inner circuit.
In addition, ammonium hydrogen
fluoride or hydrofluoric acid have great toxicity, wastewater treatment is very
difficult.What's more, polyimide is inert in concentrated sulfuric acid, so
this method is not suitable for drilling, cleaning and pitting of
rigid-flexible printed circuit board.
(2) the chromate method:
because of chromic acid has strong oxidizing, its erosion ability is strong, so
it can make the hole wall polymer material long chain disconnected, and
oxidation and sulfurization, generated in the surface more hydrophilic groups,
such as carbonyl (- C = O), hydroxyl (OH), sulfonic group (- SO3H), etc., so as
to improve its hydrophilicity, adjust the hole wall charges, and to remove the
purpose of the wall of hole drilling sewage and pitting.The general process
formula is as follows:
Chromic anhydride CrO3:400 g/l
H2SO4:350 g/l sulphate
Temperature: 50 to 60 ℃ time: 10-15 min
According to this method, the
rigid-flexible printed circuit board after drilling is defouled and corroded,
and then the hole is metallized. The metallized hole is analyzed in
metallography and tested in thermal stress.
Therefore, chromic acid method
is also suitable for drilling, cleaning and pitting of rigid-flexible printed
circuit boards. For small enterprises, this method is very suitable, simple and
easy to operate.
(3) basic potassium
permanganate method:At present, a lot of PCB manufacturers because of a lack of
professional technology, still follow rigid multilayer printed circuit board is
to drill the dirt and pitting technology - alkaline potassium permanganate to
handle just - flexible printed circuit board, the method to remove resin after
drilling sewage, at the same time can make its surface etching resin surface
produce small bumpy small holes, in order to improve the adhesion strength of
coating and the substrate of hole wall, under high temperature and high alkali
environment, swelling of the resin can be removed using potassium permanganate
oxidation drilling sewage, the system is work for the general rigid laminated,
but for just - flexible printed circuit board does not adapt,Because polyimide,
the main insulating base material of the rigid-flexible printed circuit board,
is not resistant to alkaline, it needs to swell or even dissolve a little in
alkaline solution, especially in high temperature and alkaline environment.If
this method is adopted, even if the rigid-flexible printed circuit board is not
scrapped at that time, the reliability of the equipment using the
rigid-flexible printed circuit board will be greatly reduced in the future.
3. Neutralization.After
oxidation treatment, the substrate must be cleaned and clean to prevent
contamination of the activated solution in the later process. For this reason,
it must go through the process of neutralization and reduction.
At present, the popular dry
method at home and abroad is plasma decontamination and pitting
technology.Plasma is used in the production of rigid-flexible printed circuit
board, which is mainly used for drilling and cleaning the hole wall and surface
modification of the hole wall.The reaction can be looked at is a highly active
state of plasma with the hole wall polymer materials and glass fiber of gas and
solid phase chemical reaction, the generated gas products and reaction of
particles are not drain the process of vacuum pump, is a dynamic process of
chemical reaction equilibrium. According to the first polymer materials used in
the flexible printed circuit board usually choose N2, O2, the CF4, gas was fed
as raw gas. The N2 have the effect of clean vacuum and preheating.
The schematic expression of
plasma chemical reaction of O2+CF4 mixed gas is:
O2 + CF4O + OF + CO + COF
package + + e - + F....
[plasma]
Due to the acceleration of
electric field, it becomes a highly active particle and collides with O and F
particles, resulting in high activity free radicals of oxygen and fluorine,
etc., which react with polymer materials as follows:
[C, H, O, N] +
[O+OF+CF3+CO+F+...]The CO2 + HF + H2O + NO2 +...
The reaction of plasma and
glass fiber is:
SiO2 + [O + OF + CF3 + CO + +
F...SiF4 + CO2 + CaL
At this point, we have realized
the plasma treatment of the printed circuit board.
It is worth noting that the
carbonylation reaction between O in atomic state and c-h and C=C leads to the
addition of polar groups on the polymer bonds and the improvement of the
surface hydrophilicity of polymer materials.
The rigid - flexible printed
circuit board treated by O2+CF4 plasma and then treated with O2 plasma can not
only improve the wettability (hydrophilicity) of the pore wall, but also remove
the reaction.The finished sediments and incomplete intermediates.After the
treatment of the rigid-flexible printed circuit board with direct electroplating,
the metallized hole was analyzed in metallographic analysis and thermal stress
test using plasma technology to drill dirt and cavitation, and the results
fully met the gjb962a-32 standard.
In conclusion, both dry method
and wet method can achieve the purpose of defouling and concave etching of the
rigid-flexible interconnect motherboard if the proper method is chosen
according to the characteristics of the main material of the system.
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PCB,providing 1-50 layers PCB,High quality: Blind/Buried Hole Board, High Tg
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