Cause analysis of copper free in PCB shallow thin hole
时间：【2018-08-21】 共阅【1391】次 【打印】【返回】
The problem of shallow copper-free is easy to occur in PCB manufacturing process. Some customers misjudge this type of hole as follows:
1、Tin plating agent has poor capability of deep plating (off position) and poor tin electroplating.
2、PTH is abnormal. Copper is not deposited in the hole.
3、Copper plating is poor in deep plating.
In actual production, thin copper holes are common. The reason is that there is a resistive coating on the conductive substrate (sheet metal - copper or thick copper layer) which prevents the deposition of copper. The following is the analysis of the production and prevention of this kind of resistance coating.
In the next step of circuit development, the ink on the PCB board surface is dissolved in the developer, and the developer containing ink polymer is sprayed into the PCB board surface and hole again by circulating pump. At this time, if the subsequent pressure washing (water washing water) is not enough, the ink content in the PCB board surface and hole can not be high. When the residue of the pore is washed clean, the remaining ink macromolecule compound of PCB proofing will reverse stick on the wall of the pore to form a thin layer of resistance coating. The more to the center of the pore, the worse the cleaning effect, the greater the probability of the resistance coating, especially the small hole. (Multilevel washing in the development section is only a continuous dilution of the residue, with the aim of diluting the residue as much as possible).
Understanding that the polymer anti-sticking coating is the culprit of the thinning of the copper layer in the hole, the focus of the problem is to ensure the cleaning effect in the hole to remove the anti-sticking coating. Suit the remedy to the case and cure the root.
In addition, the premise of dealing with practical problems is to face up to and respect the existing production conditions of customers, such as: line and resistance welding, dry and wet film common developer, water washing flow limited by environmental protection.
Customers had hoped to increase the amount of micro-corrosion in the pre-treatment of the diagram to remove the resistance coating in the hole, but unfortunately, it was not helpful, but fell down the micro-corrosion excessive and lead to no copper in the hole. The correct solution should be to strengthen the maintenance of the developing dry process, and the acid deoiler with good deoiling effect should be selected for the graphic and electrical pretreatment.
EC-51 acid degreaser can cooperate with customers to solve the problem of copper-free pore from the orifice to the center of the pore. The following points should be paid attention to when using EC-51 acid degreaser correctly:
1、EC-51 water washing requirements are slightly stringent, require adequate washing, because it contains wetting agent cleaning may lead to more foam copper cylinder and nickel cylinder.
2、EC-51 is specially designed for wet film, using wet film or black oil plate, if the hole can not be plated with nickel or copper, with EC-51 treatment can be solved. For thin-gauge dry film, the cylinder opening capacity should be reduced appropriately, and the content of EC-51 should be controlled to 4%. Excessive degreaser content should be prevented from attacking the edge of dry film to cause canine dentate coating. In addition, EC-51 has good copper-free effect on thin-gauge hole of dry film.
3、Winter is a high incidence of such problems (due to low temperature, poor washability), the most effective way to improve the effect of oil removal is to raise temperature (increased concentration contribution is small, but also increase the pressure of washing), temperature is generally controlled 30-35 degrees, too low temperature is not conducive to ensuring the effect of oil removal; excessive temperature is prone to degreaser attack ink and high temperature Resulting in plating. PCB is manufactured in manual line, and should also cooperate with manual swinging and adding filters to ensure the penetration of liquid in the hole. If the customer condition is bad, the EC-51 replacement cycle should be shortened to 15-20 square feet / liter.