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[technology sharing] plasma surface pretreatment in PCB board manufacturing process

With the increasing popularity of plasma processing technology, the main functions of PCB technology are as follows:

(1) hole wall etching / removal of resin from hole wall

For the general FR-4 multilayer printed circuit board manufacturing, the resin drilling and pitting removal of the hole wall after numerical control drilling usually include concentrated sulfuric acid treatment, chromic acid treatment, alkaline Potassium Permanganate solution treatment and plasma treatment.

But for the treatment of the treatment of the flexible printed circuit board and the rigid flexible printed circuit board, the effect of the chemical treatment is not ideal because of the different properties of the material, and the use of plasma to drill dirt and pitting can obtain the better roughness of the hole wall, which is beneficial to the electroplating of holes and at the same time. It has the characteristics of "three dimensional" concave erosion.

(2) activation treatment of polytetrafluoroethylene

All of the engineers who have made the metallization of polytetrafluoroethylene have the experience that the method of metallizing by the general FR-4 multilayer printed circuit board holes is a PTFE printed circuit board that can not be successfully metallized. The most difficult problem is the pretreatment of PTFE before chemical precipitation.

There are a variety of methods for the activation treatment of polytetrafluoroethylene material before chemical copper deposition, but it is concluded that the main two methods are to guarantee the quality of the product and be suitable for batch production.

(A) chemical treatment

Sodium and naphthalene are reacted in nonaqueous solvents such as tetrahydrofuran or ethylene glycol two methyl ether to form a naphthalene sodium complex. The sodium naphthalene treatment solution can etch the surface atoms of the polytetrafluoroethylene in the hole, thereby achieving the purpose of wetting the hole wall. This is a classic method of success, good effect, stable quality, and is currently the most widely used.

(B) plasma treatment method

The method is dry process, easy to operate, stable and reliable in quality and suitable for mass production. The chemical treatment of sodium naphthalene treatment solution, it is difficult to synthesize, the toxicity is big, and the shelf life is short, it needs to be prepared according to the production conditions, the safety requirements are very high.

Therefore, at present, the treatment of PTFE surface is mostly carried out by plasma treatment, which is easy to operate and obviously reduces the treatment of wastewater.

(3) carbide removal

The plasma treatment method not only has obvious effect on the treatment of various kinds of sheet material, but also shows its superiority in the field of compound resin material and micro hole. In addition, with the increasing demand for the manufacturing of the multilayer printed circuit board with higher interconnection density, a large amount of laser technology is used to make blind hole manufacturing. As the product of the laser drilling blind hole application, carbon, it needs to be removed before the fabrication process of the hole metallization. At this point, the plasma treatment technology, without exception, takes the responsibility of removing carbide.

(4) inner layer pretreatment

With the increasing demand for various printed circuit boards, higher and higher requirements for corresponding processing technology have been put forward. The inner layer of the flexible printed circuit board and the rigid flexible printed circuit board can increase the roughness and activity of the surface and improve the bonding force between the inner layer of the plate, which is also very important for the successful manufacturing.

In this regard, plasma processing technology shows its unique charm, and there are many successful examples. In addition, a certain roughness and high active surface can be obtained by plasma treatment of the printed circuit board before the coating is coated, so as to improve the adhesion of the solder mask.

(5) removal of residue

Plasma technology has three main functions in the removal of residues:

(A) in the manufacture of printed circuit boards, especially in fine lines, plasma is used to remove dry film residue / glue before etching to improve high quality wire graphics.  If the etch removal is not clear before etching, the short circuit defect will occur.

(B) plasma treatment technology can also be used to remove residual solder mask and improve weldability.

(C) for some special plates, when the plating coating layer is etched after etching, the phenomenon of shadow plating will be caused by the existence of copper particles etched on the edge of the line, which will cause the product to be scrapped when it is serious. At this time, plasma treatment technology can be used to remove the fine particles of copper by ablation and eventually achieve the processing of qualified products.