Plasma surface pretreatment in PCB manufacturing process

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Plasma surface pretreatment in PCB manufacturing process [Copy link]

With the increasing popularity of plasma processing technology, it currently has the following main functions in the PCB process:

(1) Hole wall etch-back/removal of hole wall resin smear For general FR-4 multilayer printed circuit board manufacturing, the removal of hole wall resin smear and etch-back treatment after CNC drilling usually includes concentrated sulfuric acid treatment, chromic acid treatment, alkaline potassium permanganate solution treatment and plasma treatment. However, for the treatment of removing smear from flexible printed circuit boards and rigid-flexible printed circuit boards, due to the different characteristics of the materials, if the above chemical treatment methods are used, the effect is not ideal. The use of plasma to remove smear and etch-back can obtain a better roughness of the hole wall, which is conducive to hole metallization electroplating, and at the same time has the connection characteristics of "three-dimensional" etch-back. (2) Activation treatment of polytetrafluoroethylene materials Any engineer who has carried out the metallization of polytetrafluoroethylene holes has this experience: it is impossible to obtain a polytetrafluoroethylene printed circuit board with successful hole metallization by using the general FR-4 multilayer printed circuit board hole metallization manufacturing method. The biggest difficulty is the activation pretreatment of polytetrafluoroethylene before chemical copper deposition, which is also the most critical step. There are many methods that can be used for the activation treatment of polytetrafluoroethylene materials before chemical copper deposition, but in summary, there are mainly two methods that can ensure product quality and are suitable for batch production: (A) Chemical treatment method Metallic sodium and naphthalene react in a non-aqueous solvent solution such as tetrahydrofuran or ethylene glycol dimethyl ether to form a naphthalene sodium complex. The sodium naphthalene treatment solution can corrode the surface atoms of polytetrafluoroethylene in the hole, thereby achieving the purpose of wetting the hole wall. This is a classic and successful method with good results and stable quality. It is currently the most widely used. (B) Plasma treatment method This treatment method is a dry process with simple operation, stable and reliable treatment quality, and is suitable for batch production. As for the sodium naphthalene treatment liquid of the chemical treatment method, it is difficult to synthesize, highly toxic, and has a short shelf life. It needs to be prepared according to production conditions and has high safety requirements. Therefore, at present, the activation treatment of the surface of polytetrafluoroethylene is mostly carried out by plasma treatment, which is easy to operate and significantly reduces wastewater treatment. (3) Carbide removal Plasma treatment method is not only effective in the treatment of drilling stains on various types of sheet materials, but also shows its superiority in the removal of drilling stains on composite resin materials and micro-holes. In addition, with the increasing demand for the manufacture of multi-layer printed circuit boards with higher interconnection density, laser technology is widely used for blind hole drilling. As a by-product of laser blind hole drilling, carbon needs to be removed before the hole metallization process. At this time, plasma treatment technology has unequivocally assumed the important task of removing carbides. (4) Inner layer pretreatment With the increasing demand for the manufacture of various types of printed circuit boards, higher and higher requirements are put forward for the corresponding processing technology. Among them, for the inner layer pretreatment of flexible printed circuit boards and rigid-flexible printed circuit boards, the surface roughness and activity can be increased, and the bonding strength between the inner layers of the board can be improved, which is also critical for successful manufacturing. In this regard, plasma treatment technology has shown its unique charm, and there are many successful examples. In addition, before the solder mask is coated, the printed circuit board surface can be treated with plasma to obtain a certain roughness and high activity surface, thereby improving the adhesion of the solder mask layer. (5) Residue removal Plasma technology has the following three main functions in the removal of residues: (A) In the manufacture of printed circuit boards, especially in the production of fine lines, plasma is used to remove dry film residues/residual glue before etching to obtain perfect and high-quality wire patterns. If the anti-etching agent is not completely removed after development and before etching, short circuit defects will occur. (B) Plasma treatment technology can also be used to remove the remaining solder mask and improve solderability. (C) For some special plates, when the solderability coating layer is electroplated after pattern etching, the presence of copper particles that are not etched cleanly at the edge of the circuit will cause shadow plating, which will cause the product to be scrapped in serious cases. In this case, plasma treatment technology can be used to remove the fine copper particles by ablation, and finally achieve the processing of qualified products.