Plasma Surface Pre-treatment in PCB Manufacturing Process
With the increasing popularity of plasma processing technology, there are currently the following functions in the PCB process:
(1) Hole wall erosion/removal hole wall resin drilling
For general FR-4 multi-layer printed circuit board manufacturing, the removal of hole wall resin drilling and etchback after CNC drilling is usually concentrated sulfuric acid treatment, chromic acid treatment, alkaline potassium permanganate Solution treatment and plasma treatment.
However, for the treatment of the removal of drilling dirt from flexible printed circuit boards and rigid-flexible printed circuit boards, due to the different characteristics of the materials, if the above-mentioned chemical treatment method is used, the effect is not ideal and plasma is used. Drilling and etchback can obtain better roughness of the hole wall, which is favorable for metal plating of the hole, and at the same time, has the connection characteristic of “three-dimensional” etchback.
(2) Activation of polytetrafluoroethylene
However, engineers who have conducted hole metallization of Teflon have the experience that using the method of metallization of FR-4 multi-layer printed circuit board holes, it is impossible to obtain polytetrafluoroethylene whose hole metallization is successful. Vinyl printed circuit board. The biggest difficulty is that the pre-treatment of PTFE prior to chemical copper deposition is also the most critical step.
There are several methods that can be used to activate the PTFE before the chemical copper deposition, but in summary, to ensure product quality and suitable for batch production, there are mainly the following two methods:
(A) Chemical treatment
Metal sodium and naphthalene are reacted in a non-aqueous solvent such as tetrahydrofuran or ethylene glycol dimethyl ether to form a sodium naphthalene complex. The sodium naphthalene treatment solution can etch the PTFE surface atoms in the pores, thereby achieving the purpose of wetting the pore walls. This is a classic and successful method with good results and stable quality. It is currently the most widely used.
(B) Plasma treatment
This processing method is dry process, simple operation, stable and reliable processing quality, suitable for mass production. The sodium naphthalene treatment solution of the chemical treatment method is difficult to synthesize, has a large toxicity, and has a short shelf life, and needs to be formulated according to production conditions, and has a high safety requirement.
Therefore, at present, most of the activation treatment of the surface of PTFE is performed by a plasma treatment method, and the operation is convenient, and waste water treatment is also significantly reduced.
(3) Carbide removal
The plasma treatment method not only has obvious effects on the drilling treatment of various types of sheets, but also shows its superiority in terms of composite resin materials and micro-holes in removing dirt. In addition, with the increasing demand for higher interconnect density laminated multi-layer printed circuit boards, a large number of laser technologies are used to drill blind vias as a by-product of the blind hole application of laser drilling. In this case, it needs to be removed before the hole metallization process. At this point, the plasma processing technology, without hesitation, takes on the task of removing carbides.
(4) Inner layer pretreatment
With the ever-increasing demand for various kinds of printed circuit board manufacturing, higher and higher requirements have been put forward for corresponding processing technologies. Among them, for the inner pre-treatment of flexible printed circuit boards and rigid-flexible printed circuit boards, the surface roughness and activity can be increased, and the bonding force between the inner layers of the boards can be increased, which is also critical for successful manufacturing. .
In this regard, plasma processing technology has shown its unique charm, and there are many successful examples. In addition, before the solder mask is coated, the surface of the printed circuit board is treated with plasma, and a certain surface roughness and high activity can be obtained, thereby improving the adhesion of the solder resist 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, the plasma is used to remove dry film residues/residues before etching to obtain a perfect high-quality wire pattern. If, once the etching is performed after the development, the removal of the anti-etching agent occurs, and short-circuit defects may occur.
(B) Plasma treatment technology can also be used to remove solder mask remaining and improve solderability.
(C) For some special boards, when plating the solderable coating layer after pattern etching, the phenomenon of shadow plating will be caused due to the presence of unclean copper particles on the edge of the circuit. In severe cases, the product will be scrapped. At this time, plasma treatment technology can be used to remove the copper fine particles by ablation, and finally achieve the processing of qualified products.
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