What to pay attention to SMT patch welding

SMT patch processing is the most electronic factory will be used in the placement technology, with high assembly density, light weight and other advantages, which can meet the requirements of miniaturization of electronic.And welding is a very important part in the processing of SMT patch, we need to understand the attention of its welding in order to avoid mistakes. What we should pay attention to SMT patch welding, here Wonderful PCB will give your the answer.

1. Temperature of the soldering iron head

In SMT welding due to the different temperature of the soldering iron head, the put in Rosin block will produce different phenomena.

Therefore, we must make it in the appropriate temperature, usually in Rosin melting faster and do not smoke when the temperature is the most appropriate.

2. SMT patch welding time
SMT welding time should be as far as possible to control the precise point, the general requirements from the heating point of welding to solder melting and welding points should be completed within a few seconds. In order to avoid a long time, the welding flux on evaporate completely, eventually lose their role to help, or because the time is too short, so that the temperature of the welding point is not up to the welding temperature.

3. The amount of solder and flux

Solder and flux are indispensable materials welding, reasonable selection of the solder and flux, is an important link to ensure the welding quality. For the usage of the solder and flux to control, too much will cause the solder joint coarse even next to the circuit and take the tin short circuit, may also in the process of mobile electric soldering iron solder drop caused by other parts of the short circuit; if too small, it can't cover the solder joint, the influence of welding firmness.

In the SMT welding process, we should also need to be careful not to touch welding point, especially in the welding point of the solders have not solidified completely and can not be freely moved welding of welded device and wire, otherwise, will point welding deformation,weld phenomenon, the influence of welding effect. Learn more about What is SMT technology here

FPC flexible printed circuit board material introduction

On the composition of FPC flexible printed circuit board material

Insulating Substrate

Insulating substrate is a flexible insulating film. As the circuit board insulating carrier, flexible dielectric thin film, the heat resistance of the comprehensive survey of the material requirements, covering shape performance, thickness, mechanical properties and electrical properties. Now engineering commonly used is film of polyimide (pi: polyimide with the, the name of the commodity, Kapton), ptfe:ployterafluoroethylene polyester (pet:polyester commodity name Mylar film and PTFE film. The general film thickness selection in the range of o.0127 o.127mm (0.5 ~ 5MIL). Polyimide film, polyester film and poly tetrafluoroethylene film performance comparison.

Adhesive sheet

Bonding sheet is adhesive film and metal foil, or bond films and film coverage (film). For the thin films deposited on different substrates can be used for different types of bonding sheet, such as polyester binder film and polyimide with bonding sheet is not the same, the polyimide substrate bonding sheet with epoxy and acrylic acid. Choose bonding sheet is focused on material flow and thermal expansion coefficient. No bonding sheet polyimide copper clad laminate, resistance to chemical and electrical performance is better.

Due to the low acrylic adhesive sheet of glass transition temperature, a large amount of contamination produced in the process of drilling is easy to remove, effect of metallized hole quality, as well as other adhesive materials to be unsatisfactory place, so multilayer flex circuit layer bonding piece of common polyimide material, since cooperating with polyimide substrate, the CTE (coefficient of thermal expansion (CTE) to overcome the size instability in multi-layer flexible circuit and other properties can satisfactory.

Copper foil

Copper foil is covered with adhesive in the substrate of the conductor insulating layer, after selective etching of the formation of conductive lines. This kind of copper foil most is the rolled copper foil (pcrca copper foil) or electrolytic copper foil (electrodeposited copper foil). The ductility of the wrought rolled copper foil and bending is better than that of the electrolytic copper foil, an extension of the rolled copper foil rate is 20% ~ 45%, the extension of the electrolytic copper foil rate is 4% ~ 40%. The thickness of copper foil is the most commonly used 35um (1oz), thin 18um o.5oz or thick 70UM (2oz), even 105um (for).

Coverage
The covering layer is an insulating protective layer covering the surface of the flexible printed circuit board, which can protect the surface of the conductor and increase the strength of the substrate.

First class is dry film type (coating), polyimide materials selection, without adhesive directly and after etching for the circuit boards in a laminated way pressing. The mulching requirements in the suppression of the pre forming, exposing welding part and therefore cannot meet more fine assembly requirements.

The second category is the photoreceptor development type. Sensitization development type of the first kind is covered dry film by film machine pressed in, by developing photosensitive exposed welding parts, to solve the problem of high density assembly; the second is the liquid screen printing covering materials, commonly used a thermosetting polyimide material, and photosensitive developing type flexible circuit board special solder resist ink.

More info on FPC board

Technology of SMT in PCB industry

SMT chip that is on the PCB Based on for processing series process referred to as the PCB (printed circuit board) for printing circuit board. (source: SMT is processing series process of PCB (printedcircuitboard) in the PCB infrastructure)


SMT is (surface mount technology) (an acronym for surface mounted technology), the electronic assembly industry in one of the most popular and a technical process. Electronic circuit SMT (surface mount technology, SMT), said for surface mount or surface mounted technology. It is a no pin or short lead surface mount components (SMC / SMD, the Chinese call sheet components) installed on the printed circuit boards (printed circuit board, PCB ) surface or other surface of the substrate, welding assembly of the circuit is connected by reflow soldering or other methods.

Usually we use electronic products are by the PCB and all kinds of capacitors, resistors and other electronic components according to the design of the circuit design, so all kinds of electrical appliances need different kinds of SMT processing technology to process.

SMT basic elements: the process of solder paste printing / parts mount -->AOI optical inspection / maintenance / return / welding plate.

Some people may ask answer electronic components why to do so complicated?? this fact and the development of our electronic industry is closely related to, today, the electronic products, the pursuit of miniaturization, previously used perforation plug-in components has been unable to narrow. Electronic product function can more complete, the integrated circuit (IC) has no perforated elements, especially on a large scale, highly integrated IC, had to use surface mount components. Product batch, automatic production, the factory to with low cost and high yield, produce high quality products to meet customer needs and strengthen the development of the market competitiveness of electronic components, integrated circuit (IC) open , semiconductor materials of diverse applications. Electronic technology revolution is imperative, chasing the trend. Can imagine, in Intel, amd the CPU, image processing production process of the component manufacturer strives to 20 nanometers, the SMT surface assembly technology and development is not to the situation.

SMT processing has the advantages of high density assembly, electronic products, small size, light weight, the volume and weight of the SMD components only traditional cartridge elements about a tenth of the common SMT, electronic products smaller 40% ~ 60%, the weight is lightened. High reliability and anti vibration can. Solder joint defect rate low. High frequency characteristics. Reduce the electromagnetic and radio frequency interference. Easy to realize automation, improve production efficiency. Reduces costs by up to 30% to 50%. Save material, energy, equipment, manpower and time.

Source: What is SMT Technology

3 PCB Design Experience

1. if the PCB design of the circuit system contains the FPGA device, it is necessary to use the II quartus software to verify the distribution of the pin before drawing schematic diagram.

2. 4 layer PCB board from top to bottom is as follows: the signal level, power supply and a signal plane layer; 6 layers from top to bottom in turn: signal level, signal in electric layer, signal electric layer, power supply, signal plane layer 6 layer above the plate (advantage is: anti radiation interference), priority in their choice of electric layer wiring, walk not to open plane layer prohibited line away from the ground or power supply.

3. Multiple power system wiring, such as FPGA DSP systems do six plates, at least in general will 3.3V 1.2V at 1.8V 5v.3.3v is generally the main power supply, direct shop power supply layer, through holes easily buton global power supply network.

5V generally may is the power input, need only in a small area of the copper paving. And as far as possible (you ask me the more thick, crude more rough, the thick, the better) 1.2V and 1.8V is separated from the kernel power (if the line is connected with the way will encounter great difficulties in the face of BGA devices), layout as 1.2V and 1.8V, and let 1.2V and 1.8V connected component placement in a compact area, the use of copper skin connection.

In short, because the power network throughout the entire PCB, if the use of the way the line will be very complex and will be around a long way, the use of copper clad method is a good choice!

Chinese and foreign current situation of printed circuit board industry

Printed circuit board as an important electronic components, electronic components supporting body. Due to its important role in the field of electronic components, so it is many people to become "electronic carrier". With the development of science and technology, printed circuit board is widely used in military, communications, medical, power, automotive, industrial control, smart phone, wear and other high-tech fields.

Therefore, PCB board level of production technology has gradually become an important indicator to measure the level of a national science and technology. However, compared with the developed countries of the printed circuit board industry development status and trends, China printed circuit board industry in which stage, there is what problem, how should solve. This is this article tries to answer the question.

1 Development status of printed circuit board industry in China

At present, the global printing circuit board industry development has stepped on a relatively stable period of development, has been formed, including Hong Kong, China, Japan, Taiwan, China, South Korea, the United States, Germany and the Southeast Asian region, including seven major production centers, of which Asia accounted for 79.7% of global gross domestic product.

China due to the distribution in the industrial, manufacturing cost have the advantage, has become the world's most important printed circuit board production base, 2013 circuit board output of China has occupied more than 44.2% of global output, but individual enterprises in China market occupies a smaller share, do not have a strong ability to lead to the market.

2 Development status of global printed circuit board industry

Since the middle period of the fifties of the 20th century, the PCB technology began to widely used. At present, PCB has become the "mother" of the electronic products, its applications almost penetration in the electronics industry in each end of the field, including computer, communication, consumer electronics, industrial control, medical instruments, national defense, aerospace and other fields. Future with the development of a new generation of information technology industry, smart phones, automotive electronics, led, IPTV, digital television and other new electronic products continue to emerge, market and application of PCB products will continue to expand.

In recent years, the global PCB industry overall is steady growth in 2009 due to the impact of the global financial crisis, PCB output value has declined, 2010 with global macro economy to improve step by step, PCB industry began to recover, the annual output value of 524.68 billion U. S. dollars, more than in 2009 increased substantially 27.33%.

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PCB ENIG Surface Finish

ENIG is short for Electroless nickel immersion gold. It is one of the popular PCB surface finish types. ENIG is made of electroless nickel plating and a thin layer of immersion gold, protecting the nickel from oxidation.

ENIG has several advantages. Firstly, it has excellent surface planarity, particularly helpful for PCBs with large BGA packages. Secondly, oxidation resistance is very good. Besides, its usability is suitable for untreated contact surfaces such as membrane switches and contact points. ENIG also does not wet as evenly or easily as HASL.ENIG is a expensive finish, but offers the best characteristics for printed circuit boards. The process requires the most steps compared to other common finishing types. The ENIG also has its other good characteristics, such as excellent flatness for fine pitch components, robust for multiple reflow cycles, supports alternate connections, good for in-circuit testing and press fit connectors.

The Gold readily dissolves into solder and does not tarnish or oxidize. While the Nickel strengthens the PTH and increases thermal cycle life, the Nickel barrier prevents Copper dissolution during wave solder & rework.

The electroless nickel step is an auto-catalytic process, involving depositing nickel on the palladium-catalyzed copper surface. The reducing agent with nickel ions must be filled for proper concentration, temperature and pH levels, creating a consistent coating. During the immersion gold step, the gold adheres to the nickel-plated areas through molecular exchange. This protects the nickel until the soldering process. The gold thickness needs to meet certain tolerances to ensure the nickel maintains its solderability.

Immersion Gold is replacement chemistry. In other words, it attaches to the Nickel by replacing atoms of Nickel with atoms of Gold. Immersion Gold layer is to protect the Nickel surface. The recommended Gold thickness is 2-4 µin. Its primary purpose is to maintain the solderability of the Nickel surface. Nickel, as a barrier layer to Copper, can eventually diffuse to the surface of Gold and cause the same solderability issue, which just takes place at a slower rate than Copper.


Typical ENIG specifications are defined by IPC- 4552 Specification for Electroless Nickel/Immersion Gold. The Nickel thickness must be in the range of 3-6 µm. It is sufficient to prevent porosity through the base Copper.

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