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An analysis of the causes of a tapered hole without copper

Aug 23, 2018

Hole metallization is the most important process in the PCB process. In this paper, I will talk about my personal understanding and understanding on the morphology, cause and solution of a thinning type of hole without copper.

The thinning type of hole has one common feature, that is, the copper layer inside the hole gradually decreases from the hole mouth to the center of the hole until the copper layer disappears.

The specific picture is as follows:

Some customers misjudged this type of copper hole as follows:

1. The solder polish (walking) is poor and the solder is not good;

2. PTH was abnormal, and copper was not sunk in the hole;

3. Poor copper plating capacity.

In the actual production, gradually thin holes without copper is common.

The reason lies in the existence of resistive coating on conductive substrate (plate electroplating copper or thick copper layer), which hinders electroplating copper deposition.

The production and prevention of the barrier coating are analyzed below.


In a copper or cloud thickens copper plate electric process line, during the developing process under the PCB board face not crosslinking polymerization of ink dissolved solution, contain ink polymer solution by the circulation pump spray to PCB board face and hole again, this time if the follow-up pressure water (water washing water) are unable to PCB board face and hole containing polymer ink survivor is rinsed clean, then the residual ink polymer compounds in the viscosity of hole wall to form a thin layer of resistance coating, more to the hole in the middle of the cleaning effect is worse, the greater the resistance coating appearance probability, especially through the holes.

(the multi-stage washing of the development section is just a process of continuously diluting the residue, with the aim of diluting the residue as much as possible).

After understanding that the polymer antiviscous coating is the main culprit that leads to 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 antiviscous coating.

The remedy for the disease can cure the disease.

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 film and wet film co-developing machine, water washing flow is subject to environmental restrictions.

Some customers had hoped that the microetching of the pre-treatment could remove the copper coating inside the hole, but unfortunately it did not help. Instead, excessive microetching caused the hole to be copper free.

The correct solution should be to strengthen the maintenance of the dry process of development, and choose the acid oil remover with excellent oil removal effect.

Ec-51 acid oil remover can cooperate with customers to solve the problem of no copper in such copper holes gradually thinning from the hole mouth to the center of the hole. Proper use of ec-51 acid oil remover should pay attention to the following:

1. Ec-51 water washing is slightly strict, and the water washing is required to be sufficient, because the wet agent contained in it cannot be cleaned properly, which may lead to more foam in copper cylinder and nickel cylinder.

2. Ec-51 is specially designed for wet film. Use wet film or black oil board.

For thin line spacing dry film, cylinder opening should be reduced appropriately, and the content of ec-51 should be controlled to 4%, so as to prevent excessive oil removing agent content from attacking the dry film line edge and leading to canine coating. In addition, ec-51 has good effect on the thin dry film hole without copper.

3. Winter is the time of high occurrence of such problems (due to low temperature and poor water washing). The most effective way to improve the oil removal effect is to increase the temperature (the contribution of increasing concentration is not large, but the pressure of water washing will be increased).

Too high temperature easy to produce an oil remover attack ink and lead to infiltration.

In the manual line, should also cooperate with the manual swing, the installation of filters to ensure that the hole through the liquid.

If the customer's production conditions are harsh, the cylinder replacement cycle of EC-51 should be shortened to 15-20 sq. ft/l.

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Pinsheng Electronics Co.,Ltd

Yinjin Building, Liuxian 2rd Road, 71 District of Xin'an, Bao'an District, Shenzhen, 518133, China

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