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Introduction of PCB rigid circuit board and FPC flexible circuit board production failures and solutions
PCB News
Introduction of PCB rigid circuit board and FPC flexible circuit board production failures and solutions

Introduction of PCB rigid circuit board and FPC flexible circuit board production failures and solutions

2021-11-19
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Author:iPCBer

When doing PCB pattern electroplating, PCB and FPC terminal surface treatments such as immersion gold, electro-gold, electro-tin, tin and other process treatments, we often find that the finished board has seepage at the edge of the dry and wet film or the edge of the solder mask. The phenomenon of plating, or the appearance of most of the boards, or the appearance of some parts of the boards, no matter what the situation will bring unnecessary scrap or defectiveness, which will bring unnecessary troubles to the processing of the post-stage, and even the final scrap. Heartache! Investigating the reasons, everyone usually thinks of the dry and wet film parameters, material performance problems; solder mask such as the ink for hard boards, the cover film for soft boards, or problems in printing, pressing, curing, etc. , Indeed, each of these places may cause this problem, then we are also confused that there is no problem in the above section after inspection or the problem has been solved, but there will still be seepage phenomenon, what is the reason? Didn't find out yet?

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After dry film or wet film treatment in the line section, side etching and etchback will occur during the etching of the line, resulting in insufficient line width or uneven line. The reason is nothing more than improper selection of dry and wet film materials and improper exposure parameters , Poor performance of the exposure machine, adjustment of the nozzles in the developing and etching sections, unreasonable adjustment of related parameters, improper chemical solution concentration range, improper transmission speed and other series may cause problems. However, we often find that after checking the above parameters and the performance of related equipment There is no abnormality, but there will still be problems such as line over-corrosion and pitting when making the board. What is the reason?

The circuit board will be tinned test before shipment. Of course, the customer will tin solder the components during use. It may appear in both stages, or there will be immersion tin or solder mask blistering during a certain stage. When peeling off the substrate, or even testing the peel strength of the ink on tape, when the tensile machine tests the peel strength of the soft board cover film, there will be problems that the ink can be peeled off significantly or the peel strength of the cover film is insufficient or uneven. This type of problem is especially true for customers. Customers of precision SMT placement are absolutely unacceptable. Once the solder mask blisters and peels during soldering, it will cause the original parts to be unable to be accurately mounted, resulting in the loss of a large number of components and missed work by the customer. The circuit board factory will also face huge losses such as deductions, replenishment, and even loss of customers. Then we usually When encountering such problems, which areas will you start with? We usually go to analyze whether it is the problem of solder mask (ink, cover film) material; is there a problem with the screen printing, lamination, and curing stages; is there a problem with the electroplating solution? Wait a minute, so we usually order engineers to find out the reasons one by one from these sections and make improvements. We also think about whether it is the weather? It has been relatively humid recently. Has the board absorbed moisture? (Both the base material and the solder mask are easy to absorb moisture) After some hard work, how many results can be achieved, the problem is temporarily solved on the surface, but this kind of problem occurs inadvertently, what is the reason? Those sections that may have problems have been checked and improved. What else hasn't been noticed?

In response to the above-mentioned widespread perplexities and problems in the PCB and FPC industries, we have conducted a lot of experiments and research, and finally found that an important reason for the problems of poor wiring, infiltration, delamination, blistering, and insufficient peel strength is the pretreatment. Part, including dry and wet film pretreatment, solder mask pretreatment, electroplating pretreatment and other multi-stage pretreatment parts. Speaking of this, perhaps many people in the industry can't help but laugh. The pre-treatment is the simplest. Pickling, degreasing, and micro-etching, among which the pre-treatment potion, performance, parameters and even formula, are well known by many technicians in the industry. .

The circuit board production process involves a large number of complex surface treatment solutions, such as electroplated copper, electroplated gold, electroplated tin, OSP, etching, etc. In most cases, process engineers will choose to delve into these more complex processes. Analyze; strive to master these process technologies and use them as a breakthrough point to improve their own technical capabilities. At the same time, most factories also use this as the salary standard for engineers and performance appraisal standards. Basically, there are few engineers in the pre-processing area. Carefully study, or directly purchase the finished product degreasing and microetching agent from the supplier, and use dilute sulfuric acid as the pickling liquid for pickling, and even many factories also make their own microetching, or they are equipped with persodium, perammonium system (formulation As we all know), either buy the hydrogen peroxide stabilizer and use it with the hydrogen peroxide-sulfuric acid system, and the degreasing is through the purchase of the supplier’s finished degreasing agent or the purchase of degreasing powder for dilution.

According to investigations and studies, many manufacturers have not fundamentally understood the subtle effects of the liquid chemicals in the pretreatment process, or the key effects, and only focus on the appearance of the surface, such as the degreasing section. , Fingerprints can be removed. Degreasing is OK if it is invisible to the naked eye. For the circuit board, the degreasing process is not only to peel off the oil that has been deeply bonded to the copper surface, but also to peel off the more important chemical liquid. The oil molecules are decomposed, so that no secondary pollution will be formed on the board surface. The degreasing agents and degreasing powders currently on the market usually only contain degreasing and rust removal components, while other components such as anti-corrosion agents, Surfactants, emulsifiers, and other important components are not added at all to reduce costs; even many suppliers’ formulas are purchased from elsewhere, and they do not understand the role of each component, let alone research, or combine the actual circuit board. The process needs to mix and add effective components, so in fact, the degreaser used by many circuit board factories is not a special degreaser suitable for the circuit board industry, but a traditional degreaser commonly used in the hardware and mineral processing industries. How can such a product achieve a good degreasing effect? The degreasing effect of the board can be seen with the naked eye. Actually? Through high magnification microscope or oil film test, it can be found that a large number of fine oil molecules are attached to the board surface. How can such a treatment effect ensure good adhesion, peel strength, and solderability during subsequent production of anti-corrosion layer, solder mask, and terminal surface treatment? The effect and stability of the necessary performance, such as sex, is particularly serious in our understanding of micro-etching. The micro-etching process of the circuit board industry actually has:

Remove the rust layer, oxide layer, and other foreign matter on the copper surface;
The copper surface is uniformly roughened to form a microscopic convex and concave, macroscopically flat roughening layer to achieve a roughening effect with a stable rate.
Activate the copper surface, and have a short-term resistance to gas and liquid phase corrosion, to ensure the operability of subsequent surface processing,
Low peroxide and sulfuric acid content to prevent the chemical solution from bumping and the formation of polymer organic residues on the surface,