How to solve the PCB circuit board photoresist white oil yellowing?
Printed circuit board photoresist white oil belongs to the printed circuit board photoresist ink, and photoresist ink has many common points, are composed of resin, monomer, initiator, diluent, filler, color powder, additives, the main difference is reflected in the use of different raw materials, this article is from the resin, initiator, color powder and additives to analyze the causes of photoresist white oil yellowing and improve the method.
I. Resin
The first discussion is the resin, it is known that the resin is the skeleton of the ink is essential for the photoresist white oil resin is particularly important, photoresist ink (such as green oil, black oil, blue oil) used in the resin more than o-cresol novolac epoxy resin or bisphenol A epoxy resin modified from the first graft acrylic acid to introduce a photographic group double bond, and then graft anhydride to introduce alkali developer group carboxyl group. The resin of this structure has a benzene ring structure, and the benzene ring structure is easy to produce free radicals in UV radiation and generate a conjugated system with color-emitting groups, and eventually it is easy to yellowing.
This structure of the resin made of photoresist white oil yellowing is more serious, basically can not meet the needs of customers, so the current photoresist white oil using the resin is mostly acrylic resin, generally with an epoxy group of acrylate copolymer, then grafting acrylic acid to introduce a photographic group double bond, and finally grafting anhydride to introduce alkali developer group carboxyl group.
This acrylic structure of the alkali developer resin is due to the aliphatic acrylic epoxy resin, ultraviolet light or high temperature is not easy to produce coloring groups, solid anti-yellowing effect to be more excellent.
2. the initiator
As this paper discusses the photoresist white oil, the system is naturally less photoinitiators. Photo resist ink system initiator is mostly isopropylthioanthrone (ITX), 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone (907), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl) butanone (369), this initiator system photoinitiating activity is very high, basically can meet the use of most photo resist ink, but such initiators The common characteristic is that these initiators contain sulfur, nitrogen and other heteroatoms, after ultraviolet radiation is also easy to produce chromophores and yellowing, so this initiator system is not suitable for the use of photoresist white oil.
Photoresist white oil is currently used more initiator system is not easy to produce yellowing products, such as 1-hydroxycyclohexyl phenyl ketone (HCPK), 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide (TPO), phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (819), especially TPO, it is a free radical photoinitiator, suitable for low yellowing and white system, with photobleaching effect.
Three, color powder
Photoresist ink using very little amount of color powder, generally phthalocyanine blue, phthalocyanine green and other organic color powder, the amount of additive are generally in a few parts per million to a few thousandths, and photoresist white oil using color powder is mainly titanium dioxide, the content is generally in 20-40%, the current market mainstream titanium dioxide anatase and rutile, anatase titanium dioxide in light scattering, whiteness and coverage are better, but the weather resistance to Poorer, while the anatase titanium dioxide itself on the polymer and the side effects of self-catalytic cracking aging; rutile titanium dioxide because of the surface treatment, so the weather resistance is better, photoresist white oil is made into a lot of lighting panels (such as automotive light panels, LED light panels), long-term light exposure, the weather resistance requirements are relatively high, so the preferred rutile titanium dioxide. At present, the market routinely use titanium dioxide such as DuPont R706, R960, R103, Ishihara R680, etc..
In addition, photoresist white oil in order to make people feel more white effect, generally add some blue-phase color powder in the system, the traditional blue-phase phthalocyanine blue these organic blue powder susceptible to ultraviolet light or high temperature aging, generally not used; commonly used is ultramarine, because ultramarine is an inorganic substance, not easy to dissolve at high temperatures and not easy to crack itself yellowing, in addition to ultramarine can eliminate photoresist white oil in the yellow light, to improve the effect of white. The effect of white.
4. additives
Photoresist white oil system using the resin in high temperature or long-term ultraviolet radiation will be aging process, this aging is the polymer cleavage to produce active radicals continued reaction process, and then cleavage aging yellowing, so photoresist white oil in addition to adding leveling agent, dispersant, defoamer and other general additives, you need to add the specific anti-yellowing additives, the current market use of antioxidants are mainly the following three .
4.1 Amine antioxidant
Amine antioxidant principle of action is to prevent or inhibit the chain initiation reaction and chain growth reaction by capturing peroxy radicals, thereby terminating the free radical chain reaction to prevent oxidation, in short, to achieve the anti-aging effect, such as p-phenylenediamine, phenothiazine, but it is easy to be oxidized and discolored, in the photoresist white oil is not easy to add.
4.2 Phenolic antioxidants
Bit-blocking phenolic antioxidants are phenolic compounds with spatially hindered structure, such as BASF Irganox 1010, Irganox 1076, Japan Sumitomo GA-80.
The principle of action of site-blocked phenolic antioxidants is mainly to capture the reactive free radicals to generate inactive free radicals, so that the chain reaction is terminated, the mechanism of action is as follows.
This type of antioxidant is a general antioxidant for photoresist white oil, generally not used alone, and auxiliary antioxidants with the best effect.
4.3 Auxiliary antioxidant
Auxiliary antioxidants are mainly synergistic with bit-blocking phenolic antioxidants, this category is mainly phosphite esters and thioesters, their role is mainly to destroy the polymer aging process generated by hydroperoxides, and timely stop the polymer self-oxidation process. At present, the market for these products are mainly phosphite ester class three [2.4-di-tert-butylphenyl] phosphite (commonly known as antioxidant 168).
Photoresist white oil is generally used with bit resist phenol antioxidant and auxiliary antioxidant, the market has with the product, mainly in plastic high-temperature injection molding, and the application of photoresist white oil also need to be subject to experimental results.
In the photoresist white oil development, focus on the above points, pay attention to the selection and matching of raw materials, and finally through the optimization of the formula, you can quickly develop a photoresist white oil with excellent resistance to yellowing.