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    Welding Technology

    Lead free and lead different

    Lead-free solder contains no lead and has a higher melting point than conventional (63% tin + 37% lead) solder.

    Common lead-free solder:

    · Sn-Ag (tin + silver, 96-98% tin)

    · Sn-Cu (tin + copper, 96% tin)

    · Sn-Ag-Cu (tin + silver + copper, 93-96% tin)

    · Sn-Ag-Bi (tin + silver + tantalum, 90.5-94% tin)

    · Sn-Ag-Bi-Cu (tin + silver + 铋 + copper, 90-94% tin)

    The 63/37 lead solder bath has a melting point of 183 ° C and the freezing point is also 183 ° C. Note: This solder does not appear colloidal [the same temperature point from liquid cooling to solid (or vice versa)].

    The 60/40 lead solder bath has a melting point of 191 ° C and a freezing point of 183 ° C. Note: This solder has a gelatinous state in the 8 °C range [temperature range required from liquid cooling to solid state (or vice versa)].

    Lead-free solder melting points range from 217 ° C to 226 ° C.

    Lead-free electronics

    From April 12th to 15th, the 15th China International Electronic Production Equipment and Microelectronics Industry Exhibition (NEPCON2005) was held in Shanghai as scheduled. With the participation of 700 exhibitors from 21 countries and regions, this exhibition became China. The most influential event in electronics manufacturing.

    From the perspective of exhibitors and seminars, lead-free, SMT placement machines and soldering have become the three hot spots of this exhibition. Among them, lead-free throughout the entire exhibition, from the basic solder to the lead-free upgrade of electronic equipment, all indicate that the lead-free wave is approaching, becoming the main theme of the current electronics manufacturing industry.

    Welding and lead-free become the biggest highlights

    In 2006, Europe will enforce the “Regulations on the Prohibition of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment”, so this year will be a very crucial year, which is evident from the reaction at the show. The soldering area and lead-free technology have become the highlights of this exhibition.

    Research on lead-free processes has been carried out a few years ago, and the process has matured, so it will not have much impact on the products. Lead-free solders can basically be supported by suppliers. For manufacturers, the biggest concern is cost. In addition to the cost of the solder itself, the cost of the components, connectors, etc., which can be withstand different soldering temperatures, will increase the cost.

    During the NEPCON period, Nitto Technology (Holdings) Co., Ltd. demonstrated their N2 series reflow ovens for lead-free soldering and their recently represented German Rim C2 reflow oven equipment. Liang Quan, the company's marketing director, said that the two directives on waste electrical and electronic equipment and hazardous substances proposed by the European Union provide clear standards for the healthy and stable development of the SMT industry on a global scale, allowing electronic equipment manufacturers to have development strategies. Higher requirements. At the same time, the ban has brought some pressure on Chinese electronics manufacturers to export, requiring domestic electronic equipment manufacturers to have sufficient flexibility to develop feasible development strategies according to national conditions.

    It is believed that many companies such as Electronic Assembly Materials, Kester, Senju Metal (Shanghai) Co., Ltd., Indium Technology (Suzhou) Co., Ltd., and OK Company of the United States have demonstrated their lead-free materials, including solder paste, flux, and solder wire. , preforms, solder balls and flow sealants.

    In addition, the lead-free requirements, in addition to the impact on reflow soldering, the patch device should also be changed accordingly. According to Wang Jiafa, general manager of Universal Instruments China, due to the different temperature and stress of the solder joints, the placement machine has higher requirements for pattern recognition and placement accuracy. In response to this demand, Universal Instruments has improved the performance of the newly introduced placement machine, and the placement accuracy has been doubled from the previous 50 micron to plus or minus 25 micrometers. In addition, image recognition technology has also been simulated. Processing is turned to digital processing to ensure better placement in lead-free processes.

    At present, both consumer household appliances and high-end notebook computers and communication equipment manufacturers are actively preparing for the lead-free era. Some of these manufacturers have begun to adjust the production supply chain, such as some small-volume manufacturing, including PCB circuit board design, raw material and component supply, production process equipment testing.

    The placement machine begins to focus on flexibility

    In the previous NEPCON exhibitions, the placement machine is almost one of the protagonists, and this exhibition is no exception.

    Information from this equipment supplier indicates that the speed or price of the placement machine is no longer the only competitive advantage. The overall manufacturing capacity and high cost have quickly become the focus of the manufacturer, including the flexibility, efficiency, resources and equipment of the production line. Factors such as utilization, assembly yield, and equipment upgradeability are key to maintaining long-term sustainability and strength.

    Universal Instruments Wang Jiafa said that the flexibility of the platform is crucial for customers who need to assemble various types of circuit boards every day. The assemblers of mass production do not have to worry about the complicated assembly requirements of the circuit boards. Universal Instruments can provide the most With a good solution, we can configure the corresponding assembly line for different production needs, and flexibly handle various chip placement or precision placement requirements without affecting productivity and easily balancing the production line.

    Siemens Logistics and Assembly Systems Ltd. has focused on the software optimization management system. The company's marketing director Sven Buchholz said that the system focuses on improving the efficiency of the SMT production line, while the modular design concept is flexible for users to purchase and smooth upgrade It is very convenient.

    The electronics manufacturing industry chain is getting better and better

    In addition to large-scale manufacturing equipment such as SMT placement machines and wave soldering machines, this year's NEPCON exhibition also launched three major sections: measurement and testing, electronic manufacturing services and component manufacturing, thus further improving the concept of the electronics manufacturing industry chain.

    Valor is an Israeli company that provides computer-aided engineering system software products for PCB line. This highlights the Trilogy5000 software package, Enterprise 3000 and Trec Xpert solutions.

    According to Rony Homossany, President of Wallace Technology Far East Co., Ltd., the Trilogy500 solution covers all of the PCB assembly process, integrating new product introduction, manufacturability analysis and computer-aided manufacturing into a smooth workflow; Enterprise3000 is PCB design Dedicated DFM Verification and Optimization System with 700 optimized features for physical design verification and manufacturing for PCB/MCM/HDI layout applications; Trec Xpert solution is a real-time PCB assembly control software It can monitor production in real time, improve machine performance and control inventory, and accurately track each device for overall management to optimize production processes.

    Patrick E. McGoff, vice president of the company, said that Hua Lai Technology's current customers in the Asia Pacific region include Taiwan Inventec, Foxconn and Jabil Electronics. At present, the company's global sales in 2004 reached 800 million US dollars, an increase of 20%, and is expected to maintain a high growth rate of 40% this year. He also said that in order to further strengthen sales and service capabilities in China, the number of employees will double.

    Asymtek is a global supplier of automated dispensing systems that designs and manufactures a full line of automated dispensing equipment for semiconductor packaging, printed circuit board assembly, optoelectronic assembly and precision industries, and is increasingly enriched by such equipment suppliers. Electronic manufacturing industry chain

    Mobile  repair soldering iron tip maintenance

    Mobile phone repair soldering station lead-free soldering iron head maintenance and maintenance

    1. Soldering 63% to 37% lead should be used when soldering the appropriate tin wire, and the soldering iron tip is often protected with a tin layer. In addition, we should try to use thicker tin wire for welding work, because the thicker tin wire butt welding head has more...

    1. Use the appropriate tin wire

    Solder should be used with 63% to 37% lead in soldering and often with a tin layer to protect the soldering iron tip. In addition, the thicker tin wire should be used as much as possible for the welding work, because the thicker tin wire butt welding iron head has better protection.

    2. Keep the soldering iron clean

    Use a moist, special cleaning sponge to apply flux, tin and oxide to the soldering iron tip. After each use, the soldering iron must clean the oxide on the soldering iron tip and add new tin to the tin plating of the soldering iron tip.

    3. Often apply a layer of tin to the surface of the soldering iron

    This can reduce the chance of oxidation of the soldering iron tip and make the soldering iron head more durable. After use, the new tin layer should be applied after the humidity of the soldering iron is slightly lowered, and the tin-plated layer can be used to achieve better anti-oxidation effect.

    4. Place the soldering iron on the soldering iron frame

    When soldering iron is not required, the soldering iron should be carefully placed on a suitable soldering iron frame to avoid damage to the soldering iron.

    5. Instantly clean oxides

    When the tin plating layer contains black oxide or rust, there is a possibility that the soldering iron tip cannot be tinned and the soldering work cannot be performed. If the tin-plated layer is found to have a black oxide and cannot be tinned, it must be cleaned up immediately.

    6. Choose the right soldering iron head

    It is important to choose the correct size and shape of the soldering iron. Choosing the right soldering iron can make the work more efficient and increase the durability of the soldering iron. The soldering iron tip selects the wrong soldering iron tip and affects the soldering iron to achieve the highest efficiency, and the soldering quality is also reduced.

    The size of the soldering iron tip is directly related to the heat capacity. The larger the soldering iron tip is, the larger the heat capacity is, and the smaller the soldering iron tip is, the smaller the heat capacity is. In the case of continuous welding, the larger the soldering iron tip is used, the temperature drop is reduced. In addition, due to the high heat capacity of the large soldering iron tip, it is difficult to oxidize using a relatively low temperature soldering iron tip during soldering, increasing its life.

    The short and thick soldering iron head has a long heat transfer and a fine soldering iron tip is fast and durable. A flat, blunt tip can deliver more heat than a sharp tip. In general, the size of the soldering iron is standard without affecting adjacent components. Selecting a geometry that is in full contact with the solder joints improves soldering efficiency.

    AAA. There is a temperature-regulated soldering iron. Depending on the solder used, it is important to choose the most appropriate soldering iron temperature setting. Before working, it is important to first measure the temperature of the tip with a tip thermometer.

    BBB. Use the authentic soldering iron head matched with the manufacturer

    The poor quality of the soldering iron tip, the aperture (putting into the heating core) are large and small, and the thickness of the sleeve is also different. These causes the performance of the soldering iron to be unable to play, sometimes causing the failure of the soldering iron.

    Way of soldering iron

    Grip of the soldering iron: There are three types:

    1) The anti-grip method is to hold the handle of the soldering iron in the palm with five fingers. This method is applicable to high-power soldering irons, and is connected to the welded parts with large heat dissipation.

    2) Positive grip method, the electric soldering iron used in this method is also relatively large, and most of them are curved soldering iron tips.

    3) Holding the pen method, this method is suitable for low-power electric soldering iron, welding parts with low heat dissipation, such as welding radio, printed circuit board of TV and its maintenance.

    Fourth, the use of soldering iron requirements

    1. Handling of the new soldering iron before use A new soldering iron can't be used. It must be processed before the soldering iron head can be used normally, that is, the soldering iron tip is coated with a layer of solder before use. The specific method is as follows: firstly, the iron tip is twisted into a certain shape as needed, and then connected to the power source. When the temperature of the soldering iron head rises to be able to melt the tin, the rosin is applied to the soldering iron head, and then the rosin is smoked and then coated. The upper layer of solder is so 2 to 3 times that an oxide layer is formed on the blade surface of the soldering iron tip and around it, which causes a phenomenon of "eat tin". At this time, the oxide layer can be removed and replated. Solder on the solder.

    2. Adjusting the length of the soldering iron tip When soldering the integrated circuit and the transistor, the temperature of the soldering iron tip should not be too high, and the time should not be too long. At this time, the length of the soldering iron tip inserted on the soldering iron core can be appropriately adjusted to control The temperature of the tip.

    3. There are two kinds of soldering iron heads: straight head and elbow. When using the pen holder method, the soldering iron of the straight iron head is more flexible to use. Suitable for soldering in circuits with many components. The electric iron for bending the iron head is suitable for the positive grip method, and is mostly used for welding under the vertical table of the circuit board.

    4. The soldering iron is not easy to be energized for a long time without using it, because it is easy to cause the soldering iron core to accelerate oxidation and burn, and at the same time, the soldering iron tip will be oxidized by heating for a long time, and even burned "dead" and no longer "eat tin".

    5. When replacing the soldering iron core, be careful not to connect the lead wires because the soldering iron has three binding posts, one of which is grounded, and the other two are connected to the two leads of the soldering iron core (the two binding posts pass through the power cable directly Connected to 220V AC power supply). If the 220V AC power cord is wrongly connected to the terminal of the grounding wire, the soldering iron casing will be charged and the welding part will be charged, which will cause an electric shock.

    When soldering iron is soldered, it is best to use rosin flux to protect the soldering iron from corrosion. The soldering iron should be placed on the soldering iron stand. Should be handled with care, never mess with tin on the soldering iron

    1, the use of adjustable balance temperature soldering iron is better; 2, the first time you use, you must let the soldering iron mouth "eat tin"; 3, usually do not use a soldering iron, to keep a certain amount of tin on the soldering iron mouth, can not be The soldering iron mouth is cleaned on the sponge and stored on the iron frame; 4, the sponge needs to maintain a certain amount of water to make the sponge moist all day; 5, when picking up the soldering iron to start using, you need to clean the soldering iron mouth, but in During the process of use, it is not necessary to take the soldering iron tip to the sponge for cleaning. Just put the tin on the soldering iron mouth into the tin-collecting carton, so that the temperature of the soldering iron nozzle will not drop rapidly, if there is still difficulty in tin extraction on the IC. , add some tin up (because the tin wire contains flux), you can easily extract more tin down; 6, the soldering iron temperature is between 340 ~ 380 degrees is normal, if some sensitive components only accept 240 ~280 degrees of soldering temperature; 7, soldering iron mouth, can not be treated with metal parts such as blades, but with rosin or tin wire to solve; 8, after daily use, first clean, then add tin, Then turn off the power immediately.

    Ways of Soldering SMT

    1.1 Apply flux to the solder pad before soldering, and use a soldering iron to prevent the solder pad from being tinned or oxidized, resulting in poor soldering. The chip generally does not need to be processed.

    1.2 Carefully place the QFP chip on the PCB with tweezers, taking care not to damage the pins. Align it with the pad to ensure that the chip is placed in the correct orientation. Adjust the temperature of the soldering iron to more than 300 degrees Celsius, apply a small amount of solder to the tip of the soldering iron, use the tool to press down on the chip in the aligned position, and add a small amount of solder to the pins at the opposite corners. Press and hold the chip and solder the pins at the two diagonal positions to fix the chip and not move. Re-check the position of the chip after soldering the diagonal. Adjust or remove and realign the position on the PCB if necessary.

    1.3 When soldering all the leads, solder should be applied to the tip of the soldering iron and all pins should be soldered to keep the pins wet. Touch the end of each pin of the chip with a soldering iron tip until you see solder flowing into the pins. Keep the tip of the soldering iron in parallel with the soldered lead during soldering to prevent overlap due to excessive soldering.

    1.4 After soldering all the leads, wet all pins with flux to clean the solder. Remove excess solder where needed to eliminate any possible shorts and overlaps. Finally, use tweezers to check for solder joints. After the inspection is completed, remove the flux from the board. Dip the hard brush with alcohol and carefully wipe it along the lead until the flux disappears.

    1.5 SMD RC components are relatively easy to solder, you can first put tin on a solder joint, then put one end of the component, clamp the component with tweezers, after welding one end, then see if it is correct; Once it has been put on, it will be welded to another one. If the pin is very thin, you can add tin to the chip pin in the second step, then use the tweezers to clamp the core, smear at the table, remove the excess solder, the third step is not soldering on the soldering iron, soldering directly with a soldering iron . When we finish the welding work of a circuit board, we must check, repair and repair the solder joint quality on the circuit board.

    Solder joints that meet the following criteria are considered to be qualified solder joints:

    (1) The solder joint is in an arc shape (conical shape).

    (2) The whole solder joint should be complete, smooth, without pinholes, and without rosin stains.

    (3) If there are leads, pins, their exposed pins should be between 1-1.2MM.

    (4) The shape of the foot of the part shows that the dispersion of tin is good.

    (5) Solder will surround the entire tin position and the part feet.

    Solder joints that do not meet the above criteria are considered to be unqualified solder joints and require minor repairs.

    (1) Virtual soldering: It seems that the soldering is actually not soldered. The main reason is that the pads and pins are dirty, the flux is insufficient or the heating time is not enough.

    (2) Short circuit: The foot part is short-circuited between the foot and the foot by excess solder, and also includes residual dross to short the foot and the foot.

    (3) Offset: The pin is not in the specified pad area due to the inaccurate positioning of the device before soldering or the error caused by soldering.

    (4) Less tin: Less tin means that the tin point is too thin, and the copper skin of the part cannot be fully covered, which affects the connection fixing effect.

    (5) Multi-tin: The part foot is completely covered by tin, that is, the outer arc shape is formed, so that the shape and the pad position of the part cannot be seen, and it is impossible to determine whether the part and the pad are well tinned.

    (6) Tin ball and tin slag: Excess solder balls and tin slag are attached to the surface of the PCB, which may cause short-circuiting of the small pins.

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