Wave soldering problem solving Perforated (TH) or hybrid technology circuit boards are still used in most products that do not require miniaturization, such as televisions, home audio-visual equipment, and upcoming digital set-top boxes, which still use perforated components and therefore require wave soldering. From a process point of view, wave soldering machines can only offer very little *basic* adjustment of the operating parameters of the equipment.  After the board enters the wave soldering machine on a conveyor belt, it passes through some form of flux application device where the flux is applied to the board using wave, foam, or spray methods. Since most fluxes must reach and maintain an activation temperature during soldering to ensure complete wetting of the solder joint, the board passes through a preheating zone before entering the wave tank.  Preheating after flux application gradually raises the temperature of the PCB and activates the flux. This process also reduces the thermal shock of the assembly as it enters the waveform. It is also used to evaporate any moisture that may have been absorbed or carrier solvents that dilute the flux, which, if not removed, can boil and cause spattering of the solder as it passes over the crest, or produce vapors that remain inside the solder to form hollow joints or grit.  The length of the preheat section of a wave soldering machine is determined by the throughput and conveyor speed; the higher the throughput, the longer the preheat zone is required to bring the board to the desired wetting temperature. In addition, since double-sided boards and multilayer boards have a higher heat capacity, they require a higher preheating temperature than single-sided boards.  At present, the wave soldering machine basically uses heat radiation for preheating, * commonly used wave soldering preheating methods are forced hot air convection, electric hot plate convection, electric heating rod heating and infrared heating. Among these methods, forced hot air convection is usually considered to be the most process wave soldering machine * effective heat transfer method.  After preheating, the boards are soldered with either a single wave (λ-wave) or a dual wave (scrambled wave and λ-wave). A single wave is sufficient for perforated components. When the board enters the wave, the solder flows in the opposite direction to the direction of travel of the board, creating eddy currents around the component pins. This acts as a scrubber, removing all flux and oxide film residues from the top, creating a dip when the solder joint reaches the dip temperature.  For mixed-technology assemblies, a perturbation wave is also typically used before the λ-wave. This wave is narrower and perturbed with a higher vertical pressure, which allows the solder to penetrate well into the placement of compact pins and surface-mounted components (SMD) pads between the λ-wave is then used to complete the formation of the solder joint. As components now become smaller and PCBs denser, the potential for bridging and short-circuiting between solder joints has increased. But there have been a number of effective methods available to solve this problem, one of which is the use of wind knife technology. This is in the PCB out of the wave with a wind knife to melt the solder joints blowing a beam of hot air or nitrogen, this and the PCB as wide as the wind knife can be carried out in the entire width of the PCB for complete quality control, to eliminate bridging or short-circuiting and reduce operating costs.  Other defects that can occur include false or missing solder, also known as open circuits, which can form if flux is not applied to the PCB. Top surface wetting** can occur if there is not enough flux or if the preheat stage is run incorrectly.  Although solder bridges or shorts can be detected during post-solder testing, it is important to realize that false soldering can test acceptable during post-solder quality checks and cause problems later in use. Problems in use can seriously affect the development of * low profit target, not only because of the cost of field replacement will be generated, but also because the customer found to the quality of the problem, and therefore will have an impact on future sales. Highly efficient solder antioxidant also raw materials.  In the wave soldering stage, the PCB must be immersed in the wave to apply solder to the solder joints, so the height control of the wave is a very important parameter. Can be attached to the crest of a closed-loop control to make the height of the crest to maintain a constant, will be installed in a sensor on the crest of the conveyor chain above the rail, measuring the height of the crest relative to the PCB, and then use to speed up or reduce the speed of the tin pump to maintain the correct height of the immersion tin.  The buildup of tin slag is detrimental to wave soldering. If dross collects in the tank, the likelihood

SMT reflow soldering process details Reflow soldering is the primary board-level interconnection method used in the SMT assembly process, and it offers an excellent combination of desired soldering characteristics, including ease of processing, broad compatibility with a wide range of SMT designs, high solder reliability, and low cost. However, at a time when reflow soldering is being used as an important SMT component-level and board-level interconnection method, it is also being challenged to further improve solder performance. In fact, the ability of reflow soldering technology to withstand this challenge will determine whether solder paste can continue to be the premier SMT soldering material, especially with advances in ultra-fine pitch technology. Below we will discuss some of the major issues that affect the improvement of reflow soldering performance. Undersoldering Undersoldering is the formation of solder bridges between neighboring leads. Typically, all the factors that can cause solder paste slumping can lead to under-soldering, these factors include: 1, too fast temperature rise; 2, the thixotropic properties of the paste are too poor or the viscosity of the paste recovers too slowly after shear; 3, metal loading or solids content is too low; 4, powder particle size distribution is too wide; 5; flux surface tension is too small. However, slumping does not necessarily cause undersoldering, and in soft fusion, where the melted undersolder has the potential to disconnect under the impetus of surface tension, the phenomenon of solder loss will make the undersoldering problem worse. In this case, the excessive amount of solder gathered in a certain area due to the loss of solder will make the molten solder become too much to break. In addition to the factors that cause solder paste to slump, the following factors are also common causes of under-soldering: 1, relative to the space between the solder joints, the solder paste melt too much; 2, the heating temperature is too high; 3, the paste is heated faster than the board; 4, the flux wetting rate is too fast; 5, the flux vapor pressure is too low; 6; The solvent component of the flux is too high; 7, the flux resin softening point is too low. Second, intermittent wetting of the solder film intermittent wetting is that there is water on the smooth surface, this is due to the solder can be adhered to most of the solid metal surfaces, and in the melted solder layer hidden under the cover of some of the un-wetted points, therefore, in the * first time to cover the surface with melted solder, there will be intermittent wetting phenomenon. The method of eliminating the intermittent wetting phenomenon is: 1, reduce the soldering temperature; 2, shorten the residence time of soft melt; 3, the use of flowing inert atmosphere; 4, reduce the degree of contamination. Third, low residue for the soft fusion process without cleaning, in order to obtain the decorative or functional effects, often require low residue, the functional requirements of examples include "through the flux residues tested in the circuit to probe the test cladding layer and in the insertion of joints and cladding layer or in the insertion of joints and soft fusion soldering near the point of contact between the through-hole of the implementation of electrical contact "Higher amounts of flux residue often result in excessive residue coverage of the metal surfaces to be electrically contacted, which prevents the establishment of an electrical connection, a growing concern in the face of increasing circuit densities. Obviously, low residue solder pastes which do not require cleaning are an ideal solution to this requirement. However, the associated soft-melt necessity complicates the problem. In order to predict the soldering performance of low-residue solder pastes in different levels of inert soft-melt atmospheres, a semi-empirical model is proposed, which predicts that the soldering performance improves rapidly as the oxygen content decreases, and then gradually levels off. Experimental results show that the solder strength and the wetting ability of the solder paste increase as the oxygen concentration decreases, and furthermore, the solder strength increases with the increase of the solids content in the solder flux. increase. The model presented by the experimental data is comparable and provides strong evidence that the model is valid and can be used to predict the solder properties of solder pastes and materials, therefore, it can be asserted that an inert soft melting atmosphere should be used in order to successfully employ low residue solder without cleaning in the soldering process. Fourth, the gap The gap is the absence of a solder joint between the component leads and the circuit board solder joints. Generally, this can be attributed to the following four reasons: 1, insufficient solder deposition; 2, poor lead coplanarity; 3, insufficient wetting; 4, solder loss dates

Analysis and countermeasures of the "monument" phenomenon In the surface mount process of reflow soldering process, chip components will produce due to warping and desoldering defects, people image called "vertical monument" phenomenon (i.e. Manhattan phenomenon). The "monument" phenomenon occurs in the CHIP components (such as chip capacitors and chip resistors) reflow soldering process, the smaller the size of the component is more likely to occur. The reason for this is that the solder paste on the pads at both ends of the component is not balanced in terms of surface tension between the two soldered ends of the component when it is melted in reflow. "Vertical monument" specific analysis of the following seven main reasons: (1) uneven heating uneven temperature distribution in the reflow oven uneven temperature distribution of the board surface 2) Problems of components The shape and size of the weld end varies greatly The weldability of the weld end varies greatly The weight of the components is too light (3) Material and thickness of the base plate Poor thermal conductivity of the base plate material Poor thickness uniformity of the base plate (4) Shape and solderability of pads Large difference in heat capacity of pads Large difference in solderability of pads (5) Solder paste Poor flux uniformity or activity in solder paste Large difference in thickness of solder paste between two pads Too thick solder paste Poor printing accuracy, serious misalignment 6) Preheating temperature Preheating temperature is too low (7) Poor mounting accuracy, severe component offset. The "monument" phenomenon is the result of a mixture of the above factors, the following is a brief analysis of these major factors. Welding method Incidence GRM39 (1.6×0.8×0.8mm) GRM40 (2.0×1.25×1.25mm) Vapor-phase heating 6.6％ 2.0％ Infrared hot air reflow soldering 0.1% 0 Preheating period: Table 1 is the infrared heating and gas-phase heating reflow soldering in the vertical monument phenomenon in the test statistical results, in the test used 1608 and 2125 chip capacitors, the test is infrared and hot air reflow soldering and no preheating of the gas-phase heating reflow soldering, from the table can be clearly seen in the vertical monument phenomenon of the incidence of the latter is much greater than the former, which is due to the gas-phase heating without a preheating zone, so that the temperature rise is very fast, and the results Components at both ends of the paste does not melt at the same time the probability of greatly increased. Preheating temperature and time is quite important, we were on the preheating time of 1-3 minutes, preheating temperature of 130-160 degrees under the conditions of reflow soldering test statistics, the results can be clearly seen, the higher the preheating temperature, preheating time is longer, "vertical monument" phenomenon of the incidence of the lower. We test the preheating * high temperature is 170 degrees, slightly higher than the normal production preheating temperature to be a little higher, found that the preheating temperature rose from 140 degrees to 170 degrees, the "monument" phenomenon occurs greatly reduced. This is because the higher the preheating temperature, into the reflow soldering, components at both ends of the temperature off the smaller, the closer the two ends of the solder paste melting time. But the longer the solder paste is at a higher preheating temperature, the more serious the degradation of its flux, the worse the flux, the more likely to produce welding defects. The test results of the relationship between the pad size pad size and the incidence of vertical monument phenomenon, it is clear that when B and C decreases, the incidence of vertical monument phenomenon decreases, but when C is less than 0.7mm, with the decrease of C, the incidence of defects of component displacement increases significantly. Tests found that the pad spacing from 2.8mm reduced to 2.0mm, "vertical monument" phenomenon has reduced the incidence of 90%, only one-tenth of the original. This is because the size of the pad is reduced, the amount of solder paste coating is reduced accordingly, the surface tension of the solder paste melting is also followed by a reduction. So in the design, under the premise of ensuring the strength of the solder joints, the pad size should be as small as possible. Solder paste thickness printing template thickness of 20UM when the incidence of vertical monument phenomenon is much greater than the template thickness of 100UM when the situation. This is because 1, reduce the thickness of the mold, is to reduce the amount of paste, paste melting surface tension decreases. 2, reduce the thickness of the mold, so that the paste is thinner, the entire heat capacity of the pad is reduced, the probability of two pads on the paste melt at the same time greatly increased. Mounting accuracy in general, mounting components generated by the offset, in the reflow p

How cell phones work Cell phones can communicate with each other, mainly by three parts of the coordinated work of the results Respectively for the radio frequency part, the logic part and the power part, to understand the working principle of the cell phone in fact, as long as you understand how these three parts work on it First: radio frequency part Usually the radio frequency part, and by the receiving signal part and send signal part composition. Cell phone in the receiving signal, the first use of the antenna to receive the 935-960MHz RF signal, through the U400, SW363, the receiving signal will be separated from the transmitting signal, so that the send and receive do not interfere with each other. The fourth pin input and fifth pin output from U400 enter the receiving front-end circuit, and the working state of U400 is controlled by the third pin potential, which is in turn controlled by the TXON and RXON signals from the CPU. The RF signal after the antenna switch is first filtered by band-pass filter FL451 and then sent to high-frequency amplifier Q418 for amplification, and the output of Q418 is filtered by FL452 and then sent to Q420 mixer tube for frequency mixing. And the local oscillation signal generated by RXVCO, and FL453 filtered and sent to the base of Q420 for mixing, take the difference, from the collector of Q420 output 153MHz IF signal, filtered by FL420 to get 153MHz pure medium diesel signal, now amplified by the Q421 sent to the 31 feet of the U201, 153MHz IF signal with the The 153MHz IF signal and the 153MHz carrier signal are demodulated in 32D53 to produce RXI and RXQ analog baseband signals, which are sent to U501 at pins 14# and 15# via U201 at 46# and 48#. After A/D conversion in U501, it is sent to the digital signal processor for further processing. 153MHz carrier wave is connected to the 306MHz oscillator circuit composed of peripheral circuits by U201's 41#, 42#, and 43# to form the 306MHz flue-wave signal, which is dichroicly formed into a 153MHz carrier wave. For the transmitting part, the TXIN, TXIP, TXQN, TXQP transmit band signals output from 21#, 22#, 23#, 24# of the 501 enter 61#, 62#, 63#, 64# of the U201. 6#, 7#, 10# of the U201 are connected externally to a 216MHz VCO to generate a 216MHz carrier signal, which is divided by a frequency divider in the U201 to generate a 108MHz carrier signal. The signal is divided by the frequency divider in U201 to generate a 108MHz transmitter IF signal. Four modulation signals in U201 to complete the 108MHz carrier modulation from the fourth pin output to the U300 4 # U300 to complete the launch sampling signal and TXVCO phase gentle frequency, take the difference between the 108MHz signal and the 4 # input TXIF phase identification, resulting in phase identification error voltage from the eighth pin output to control the capacity of the varactor diode CR300 to change the oscillating frequency of TXVCO, from the C pole of Q300 to change the frequency of TXVCO, from the C pole of Q300 to change the frequency of TXVCO, from the C pole of Q300 to change the oscillating frequency of TXVCO. Frequency, from the C pole of Q300 output 890-915MHz transmitter signal by Q301 preamplifier and Q302 drive into the amplifier Q302, amplified signal into the antenna U400 pin 1, and then from the U400 4 # send antenna to transmit out. II: Logic Part In the logic part, the received RXI, RXQ analog baseband signals in the modem U501 internal D / A conversion, decryption and adaptive equalization will be completed after the digital baseband signals from the U501 6 # sent to the CPU 10 # in the CPU for channel decoding, remove the error correction code source as well as take the real control information, the restoration of the voice data flow through the data line and the address line, transmitted to the voice device U801 for decoding. U801 for decoding. The resulting digital voice signal is sent from 78# of U801 to 8# of PCM***U803. Digital voice signals in the PCM **** completed decompression and A/D conversion, and then through the digital volume positioner, the received signal, volume adjustment, and then by the U803 of 4 #, the output analog audio signals to the U900 6 # and 21 #. 6 # input ringing signal, by the internal ringing drive support amplification, from the U900 of 4 #, 5 # output to drive the ringer to send between the audio signal, from 21 # input, through the internal ringing drive support amplification, from the U900 of 4 #, 5 # output to drive the ringer to send between the audio signal, from the U900 of 4 #, 5 # output to drive the ringer to send between the audio signal. Input from 21#, after the internal audio amplifier, from 19#, 20# output amplified voice signal to drive the earpiece sound. When our users are talking, the voice through the earpiece after the conversion of sound and electricity into the power supply integrated circuit U0- 9 #, after the internal audio amplifier, from 10 # output amplified analog audi

Methods to improve the placement efficiency of smt placement machine How to improve the placement speed of smt mounter, I believe that many smt industry friends have encountered such a problem. SMT machine is in the case of not causing any damage to the device and the base board, stable, fast, complete, correctly sucking the device, and quickly and accurately mount the device in the specified position, is now widely used in home appliances, communications, computers and other industries. SMT equipment in the purchase of the main considerations of its mounting accuracy and mounting speed, in the actual use of the process, in order to effectively improve product quality, reduce the cost of production in favor of improving production efficiency, then how to improve and maintain the SMT equipment mounting rate is the primary issue in front of the user. First: the meaning of the mounting rate Mounting rate refers to the actual number of devices mounted in a certain period of time and the ratio of the number of suction, that is: Mounting rate = × 100% Sucking number The total number of discarded pieces refers to the number of suction errors, the number of recognition errors, the number of standing pieces, the number of lost, and recognition errors and device specifications size error and device optical recognition of two kinds of bad. Mounter whether it is a small machine, medium-sized machine, large machine, whether it is a medium-speed machine, high-speed machine, they are mainly by the device storage and transportation devices, XY table, mounting head and control system components. The mounting head is the core and key components of the mounter, the mounting head generally has a fixed head and rotary head points, fixed general multi-head arrangement, as few as 1, as many as 8, can be taken at the same time or individually, the rotary head is divided into the horizontal plane rotation and rotation in the vertical plane. A: device suction Nozzle pickup height switching B: θI rotation (±90') C: Device optical recognition D: Device Attitude Detection θ2 rotation (±90') E: Mounting device/nozzle height switching F: θ3 rotation (±180'-θ) Nozzle home position detection of defective products elimination G: Nozzle switching H: Nozzle number detection According to the mounter from the pick and place the whole process, purely from the equipment side, in the correct setting of the nozzle pick height, picking up pieces of the center of the nozzle and the relative position of the feeder, the main factors affecting the placement rate of the device is to pick up pieces of the position, according to the equipment statistics of the production of information intelligence, and its impact accounts for the impact of the whole factor of more than 80%. And the causes are: on the one hand is the device storage and transportation device on the feeder, on the other hand is the suction nozzle, both in the feeder of the film about 60%, 40% or so is due to the suction nozzle pollution caused. Second, the impact of smt mounter feeder The impact of the feeder master concentrated in the feeder abnormal. Feeder drive motor drive, mechanical drive and cylinder drive and so on several kinds, here to mechanical drive as an example, explains the impact of the feeder on the mounting rate: 1: drive part wear Mechanical drive by the cam spindle drive feeding mechanism, quickly knocking to find the feeder to find the arm, through the connecting rod so that the ratchet connected to the components driven by the braided belt forward a distance, while driving the plastic tape disk will be braided on the plastic tape cap away from the suction nozzle down to complete the pickup action. However, due to the feeding mechanism of high-speed access to the feeder, after a long period of use, the feeder pawl wear and tear serious, resulting in the pawl can not drive the tape reel plastic tape normal peeling, so that the suction nozzle can not complete the work of taking pieces. Therefore, before installing the tape should carefully check the feeder, the pawl wheel has been worn feeder should be repaired immediately, can not be repaired should be replaced in a timely manner. 2：Feeder structure deformation Due to long-term use or improper operation of the operator, its pressure belt cover plate, thimble, spring and other movement mechanism to produce deformation, corrosion, etc., which leads to the device suction bias, standing piece or suction can not be devices, therefore, should be regularly inspected, found that the problem is handled in a timely manner, so as to avoid a large amount of waste of the device, and at the same time in the installation of a total of the feeder should be installed correctly and securely installed in the feeder section platform, especially without the height of the feeder detection of the device, or may result in the feeder or the feeder, or the feeder should be replaced immediately. Otherwise it may cause damage to the feede