PCB Causes and countermeasures of insufficient strength of penetration plating

- Jul 26, 2018-

The following problems are often encountered in the production of PCB rigid circuit boards and FPC flexible circuit boards:
First, after dry film or wet film treatment, side erosion and concave corrosion occur in etching lines, resulting in insufficient line width or uneven lines.The reason is not only because of the improper selection of dry and wet film materials, improper exposure parameters, poor performance of the exposure machine.Developing, etching section nozzle adjustment, related parameters adjustment is not reasonable, the concentration range of the liquid medicine is not appropriate, transmission speed is not appropriate and so on series may lead to the cause of problems.However, we often find that there is no abnormality in the performance of the above parameters and related equipment after inspection. However, problems such as line over-erosion and concave corrosion will still occur when making the plate.What's the reason?
Ii. In the process of PCB graphic plating, PCB and FPC terminal surface treatment, such as gold sink, electric gold, electric tin, tin melt, etc.We often find that the made plate in the dry and wet film edge or the edge of the welding resistance layer, or most of the plate, or parts of the plate appear, no matter which situation will bring unnecessary scrap or bad for the post-processing section, or even the final scrap, heartbreaking!It is often thought that the dry and wet film parameters, the material performance problems;Resistance to soldering such as inks for hard plates, overlays for soft plates, or problems in printing, pressing, curing, etc.Indeed, every one of these places can cause this problem.Then we are also confused that there are no problems or problems in the above sections after inspection, but there will still be infiltration plating.What is the cause that hasn't been found out?
Third, the circuit board will do the tin test before shipment. Of course, the customer will use the tin soldering elements.It is possible that both stages will occur, or at a certain stage when tin immersion or soldering occurs, the resistance welding foaming, stripping the substrate.Even when the adhesive tape tests the peel strength of ink, when the tensile machine tests the peel strength of the covering film of the soft plate, there will be problems that the ink can be obviously stripped off or the peel strength of the covering film is insufficient or uneven.This kind of problem customers, especially those who make precision SMT packaging, are absolutely unacceptable.Once the resistance layer has blister stripping during welding, it will not be able to accurately mount the original.Lead to customer loss of a large number of components and late work.At the same time, the circuit board factory will face huge losses such as deduction, material supplement and even loss of customers.So what do we usually do when we encounter such problems?We usually analyze the problem of soldering (ink, coating film) material.Is there a problem with screen printing, laminating and curing stage?Is there a problem with the plating solution?Wait...So we usually tell engineers to make sure they look at each of these sections and make improvements.We wonder if it's the weather?It's been wet recently. The boards are getting damp.(base material and resistance welding are easy to absorb moisture) after a hard battle, how much can gain some effect, the problem has been temporarily solved on the surface.However, inadvertently this kind of problem occurred again, what is the reason?Those sections that may have problems have been clearly improved.What else is missing?

For the above belong to PCB, FPC industry wide confusion, problems.We carried out a lot of experiments and researches, and finally found that one of the important reasons for the problems of poor circuit, infiltration plating, stratification, foaming, and insufficient peel strength lies in the pretreatment part.Including dry and wet film pre-treatment, resistance welding pre-treatment, electroplating pre-treatment and other pre-treatment sections.At this point, perhaps many in the industry can't help laughing.Pretreatment is the simplest, pickling, degreasing, and micro-etching.Which of these pre-treatment potions, performance, parameters, and even formulations are clear to many technicians in the industry.The production process of circuit board involves a lot of complex surface treatment potions, such as electroless copper, electroless gold, electroless tin, OSP, etching, etc.These more complex processes in most cases, the process engineers will choose to delve into, analyze;Strive to master these technologies, and as a breakthrough point to improve their technical capabilities.At the same time, most factories also use this as the salary standard of engineers, performance appraisal standard.There are few engineers who have studied this area carefully before.Or buy the finished products from the supplier directly, such as oil remover, microetchant, acid pickling itself with dilute sulfuric acid as acid lotion.Even a number of factories have their own microcorrosion, either with sodium, ammonium system (known formula), or buy hydrogen peroxide stabilizer with their own hydrogen peroxide - sulfuric acid system.Deoiling is diluted by purchasing the supplier's finished deoiling agent or purchasing the deoiling powder.According to our investigation and research, many manufacturers did not understand the subtle effects, or key effects, of each liquid in the pretreatment process from the bottom up, and only paid attention to the surface appearance effect.If the oil removal section, you may always think that the oil can be removed from the board, finger printing can be removed, the naked eye can not see that is oil removal OK, little imagine that the oil removal process for the circuit board is not only the deep combination of the copper oil peeling off, but also the more important liquid medicine can be stripped off the oil molecules.Only in this way can there be no secondary pollution to the surface.The oil remover currently sold in the market, oil remover powder, usually contains only oil removal and rust removal components, while other components such as corrosion inhibitor, surfactant, emulsifier and other important groups are divided into cost reduction without adding at all.Even the formulations of many suppliers are purchased from other places, and they do not understand the function of each component at all, let alone research, or combine with the actual process requirements of circuit boards to add effective components.In fact, many circuit board factories used the oil removal agent is not suitable for the circuit board industry dedicated oil removal agent, but the general hardware, mineral processing industry, the traditional oil removal agent.Such a product how to achieve good degreasing effect, the surface of the plate with the naked eye looks good degreasing effect.Actually?We can find a large number of fine oil molecules attached to the plate by high power microscope or oil film test.How can such treatment effect guarantee the effect and stability of necessary performance in the subsequent production of anti-corrosion layer, anti-welding layer and terminal surface treatment?What is particularly serious is our understanding of microerosion.In fact, the micro-etching process of circuit board industry should have 1.2. Evenly coarsened copper surface, forming micro convex and concave, macroscopic flat coarsening layer.The coarsening effect is stable.3. Activate the copper surface, and have the effect of short-term anti-gas and liquid phase corrosion, so as to ensure the operability of subsequent surface processing.4. Low peroxide and sulfuric acid content, preventing the liquid from boiling violently and forming the residual polymer organic matter surface.In actual production, most of the microetch solutions we have prepared or purchased are regarded as etch solution.It is believed that only the rust stain on the surface of the plate removed foreign matter, can expose fresh copper surface is to achieve the micro-corrosion effect.And in fact?Peroxides such as hydrogen peroxide, sodium persulfate, ammonium persulfate, etc., and strong acids such as sulfuric acid in our self-prepared microsolution.Content was high in order to effect, such as peroxide content in 120 and 150 grams/liter, sulfuric acid content more than 5%, such a high concentration is actually a micro erosion into the etching, was the large number of copper corrosion, and because of the addition of no regulator, bit different corrosion depth shallow, light, led panel processing effect is not consistent, or secondary rework that lead to serious bite erosion of the copper layer to section after processing, cause scrap.Many hydrogen peroxide systems also make the common mistake of assuming that even microerosion can be achieved by adding hydrogen peroxide stabilizers.Hydrogen peroxide stabilizers are added only to inhibit the rapid decomposition of hydrogen peroxide.In fact, the professional micro-corrosion agents used in the PCB industry should be supplemented with low-foaming surfactants, special wetting agents, organic complexing agents, micro-determination agents, anti-corrosion agents and other additives.In this way, the corrosion rate of peroxide and sulfuric acid is too fast, and the content of main components with high side reaction products is reduced as much as possible, and the pharmaceutical liquid is more stable. Besides the basic function of rust removal, the copper surface can be even and stable.And microscopic achieve uniform convex concave coarsening layers (to follow-up the wet and dry films, resistance welding layer processing), antioxidants and strong acid alone does not actually increase the ideal copper surface coarsening area, must join the active agent, wetting agent, etc in order to achieve good depth coarsening effect, increase the copper surface coarsening area, from surface finishing of bonding strength and peel strength.After improvement and improvement, the integrated microetch solution for PCB should be: no boiling of liquid, no pollution of macromolecular by-products, good rust removal ability, good uniform and flat appearance, deep coarsening of copper surface, small amount of corrosion copper.To achieve the smooth surface of the plate, resistance welding or coating processing when strong binding.
With the transformation of PCB to ultra-thin copper type, we need more and more a kind of micro-etching solution with less amount of copper etching (and the effect of rust removal and coarsening).
As the line precision of circuit board is more and more high, we need a kind of oil removal and micro-etching liquid with better pretreatment effect more and more.To ensure the anti-permeability of the corrosion layer (dry and wet film).
As the appearance requirement of PCB terminal surface treatment becomes higher and higher, we need to introduce high quality pretreatment technology.
Model transformation, as the surface welding to lead-free welding temperature of the circuit board need to bear more and more high, the thermal shock resistance of the surface resistance welding layer demand is higher and higher, to the terminal surface treatment and resistance welding layer (film) ink, cover of peel strength, and the adhesion strength of the base copper demand is becoming more and more high, we need a has better effect of pretreatment process for protection.
With the increasingly fierce competition in the PCB industry, we need to improve our process to improve the product yield and gain profit growth.High quality pre-treatment potions can certainly help us at a low cost.
The leading edge of PCB industry, such as Japan, the United States, Korea and Taiwan, has been paying attention to and using the new generation of pretreatment technology.Make the products produced more competitive and stable.The small belt is large, and the previous treatment should be carried out to ensure the stability of the whole process.