PCB surface treatment of five common characteristics and use-PCB-screen special printing industry

PCB surface treatment of five common characteristics and use-PCB-screen special printing industry

1. INTRODUCTION As human demands for continuous improvement of living environment, the current PCB production process involved in environmental issues is particularly prominent. Currently the subject of lead and bromine are the most popular; lead-free and non-halogenated will influence many aspects of PCB development. Although the present situation, PCB's Surface Treatment Changes in technology is not great, as is quite a long way off, but it should be noted: the slow long-term changes will lead to dramatic changes. In Environmental protection Voice rising case, PCB surface treatment process changes will happen definitely next.

2. The purpose of surface treatment

Surface basic aim is to ensure good solderability or electrical performance. As the nature of copper oxides in the air tend to exist in the form, probably not long remain of the original copper, copper needed for other processing. Although follow-up assembly, you can use to remove most of the strong flux of copper oxides, but the strong flux itself is not easily removed, the industry generally does not use strong flux.

3. Common surface treatment of five

There are many PCB surface treatment, commonly HASL, organic coating, electroless nickel / Immersion Gold, Immersion Silver, and the five dip tin process, the following will go through.

1. HASL Hot Air Leveling also known as hot air solder leveling, which is coated with molten tin PCB surface and the whole heated compressed air (blowing) peace process, to form a layer of both the resistance to copper oxidation, but also provide a good the weldability of the coating layer. HASL solder and copper, usually in the form of copper binding sites tin intermetallic compound. To protect the copper surface of solder thickness about 1-2mil.

PCB for HAL should always immersed in molten solder; air knife blow before the solder solidification of the solder liquid level; air knife to the crescent-shaped solder copper surface to minimize and prevent solder bridging. Hot Air Leveling divided into two kinds of vertical and horizontal, is generally believed that horizontal well, mainly horizontal HASL coating uniform, and can realize automatic production. Hot Air Leveling Technology General procedures: The micro-corrosion coating flux preheated tin cleaning spray.

2. Organic coating Organic coating process is different from other surface treatment, it is in the air between copper and act as a barrier layer; organic coating process is simple, low cost, making it widely used in the industry. Early molecular organic coating is rust from the role of imidazole and benzotriazole, the latest molecular mainly benzimidazole, which is the chemical bonding of nitrogen functional groups to the copper on the PCB. In the subsequent soldering process, if only the copper surface layer of organic coating layer is impossible, there must be a lot of layers. This is why the chemical tank usually need to add copper solution. In the first layer coating, the coating layer adsorption of copper; then the second layer of organic coating and the copper binding molecule, until 20 or even hundreds of organic molecules assembled in the copper coated surface, so you can return several times to ensure reflow soldering. Results show that: the latest organic coating process can be repeated to maintain a good lead-free soldering process performance.

Organic coating process of the general process: degreasing Etching acid water washing cleaning organic coating, process control, surface treatment process compared to other more easily.

3. Electroless Nickel / Immersion Gold Electroless Nickel / Immersion Gold Process not as simple as the organic coating, electroless nickel / Immersion Gold PCB like to wear thick armor; other Electroless Nickel / Immersion Gold Process Unlike the organic coating as the anti- rust barrier layer, it can be useful during long-term use PCB and achieve good electrical properties. Therefore, electroless nickel / Immersion gold is wrapped in a thick layer of copper surface, good electrical properties of nickel gold alloy, which can be long-term protection PCB; In addition, it also has other surface treatment not available in the environment of the patient sex. Nickel is due to be interdiffusion between gold and copper, and nickel layer to prevent the spread between gold and copper; If there is no nickel, gold will be spread to the copper in a few hours to go. Electroless Nickel / Immersion Gold, another advantage is the strength of nickel, nickel thickness of only 5 microns high temperatures can limit the expansion of Z direction. In addition, electroless nickel / Immersion Gold also can prevent the dissolution of copper, which will benefit the lead-free assembly.

Electroless Nickel / Immersion Gold Process general procedures: acid cleaning Etching prepreg activation Electroless Nickel Immersion Gold, there are six major chemical tanks, involving nearly 100 kinds of chemicals, so process control more difficult.

4. Immersion Silver Immersion Silver process between the organic coating and electroless nickel / Immersion gold between the process is relatively simple, rapid; not Electroless Nickel / Immersion Gold as complex, nor is it to put a thick layer of armor PCB , but it can still provide good electrical properties. Silver is golden little brother, even if exposed to heat, humidity and pollution, environment, banks are still able to maintain good solderability, but will lose their luster. Silver does not have the dip Electroless Nickel / Immersion Gold possess good physical strength because there is no nickel-silver layer below. Another good store of silver dip, dip up a few years after the assembly of silver would not be big problems.

Baptist replacement reaction of silver is that it is almost pure silver coated sub-micron level. Sometimes the process of leaching of silver also contains organic compounds, mainly silver corrosion prevention and elimination of silver migration problems; generally difficult to measure out the organic layer, analysis shows that less than 1% of the weight of the organism.

5. Soldering Are due to all the current tin-based solder, so the layer of tin solder with any type of match. From this point of view, most have a dip tin process development prospects. However, by the previous PCB after solder dip tin process must, in the welding had to be, and Xi Cheng Zhongxi migration will bring reliability, so Soldering technology adoption is limited. Later in the dip solution, the addition of organic tin Additive Can be made of tin structure of granular layer structure to overcome previous problems, but also has good thermal stability and weldability.

Dip tin process can form a flat copper tin intermetallic compounds, this feature makes the dip and the hot air solder leveling with the same good weldability without the hot air leveling flat headache problem; dip tin no Electroless Nickel / Immersion Gold metal between proliferation?? copper tin intermetallic compounds can be strong together. Dip tin plate can not be stored for too long, assembly must be based on the order in dip tin.

Attention to business innovation change process management to find new ideas?? Command of the 2010 special screen printing industry of China Development Forum

"Zhen Xing Cup" 2009 China Top Ten selection screen printing special awards ceremony

More exciting, please see>>

POST COMMENT

Buying Discount Ink Cartridges A Reply Letter: Dvd Creator For Your Christmas Gift Preparation Advantages of a desktop computer Affiliate programs Making Extra Money Online The Difficult Options In Poster Printing How to pick a printer New Canon Black and White Photocopiers/Printers – A Winner at On Demand Have Complete Control Over Your Computer Using Keylogger Software Professional Photo Printing For Professional Results quot;Cultural Industry Promotion Plan" release (full text) - the cultural industry, revitalize - Printing Industry Canvas Photo Printing For Art Reproductions DIY Home Photo Printing A Good, above Average entry level Laptop PC