Technical Library | 2019-09-11 23:33:04.0
There are numerous techniques to singulate printed circuit boards after assembly including break-out, routing, wheel cutting and now laser cutting. Lasers have several desirable advantages such as very narrow kerf widths as well as virtually no dust, no mechanical stress, visual pattern recognition and fast set-up changes. The very narrow kerf width resulting from laser ablation and the very tight tolerance of the cutting path placement allows for more usable space on the panel. However, the energy used in the laser cutting process can also create unwanted products on the cut walls as a result of the direct laser ablation. The question raised often is: What are these products, and how far can the creation of such products be mitigated through variation of the laser cutting process, laser parameters and material handling? This paper discusses the type and quantity of the products found on sidewalls of laser depaneled circuit boards and it quantifies the results through measurements of breakdown voltage, as well as electrical impedance. Further this paper discusses mitigation strategies to prevent or limit the amount of change in surface quality as a result of the laser cutting process. Depending on the final application of the circuit board it may prompt a need for proper specification of the expected results in terms of cut surface quality. This in turn will impact the placement of runs and components during layout. It will assist designers and engineers in defining these parameters sufficiently in order to have a predictable quality of the circuit boards after depaneling.
Technical Library | 2024-04-29 21:39:52.0
In this paper, we develop and put into practice an Automatic Optical Inspection (AOI) system based on machine vision to check the holes on a printed circuit board (PCB). We incorporate the hardware and software. For the hardware part, we combine a PC, the three-axis positioning system, a lighting device and CCD cameras. For the software part, we utilize image registration, image segmentation, drill numbering, drill contrast, and defect displays to achieve this system. Results indicated that an accuracy of 5µm could be achieved in errors of the PCB holes allowing comparisons to be made. This is significant in inspecting the missing, the multi-hole and the incorrect location of the holes. However, previous work only focusses on one or other feature of the holes. Our research is able to assess multiple features: missing holes, incorrectly located holes and excessive holes. Equally, our results could be displayed as a bar chart and target plot. This has not been achieved before. These displays help users analyze the causes of errors and immediately correct the problems. Additionally, this AOI system is valuable for checking a large number of holes and finding out the defective ones on a PCB. Meanwhile, we apply a 0.1mm image resolution which is better than others used in industry. We set a detecting standard based on 2mm diameter of circles to diagnose the quality of the holes within 10 seconds.
Technical Library | 2019-08-07 22:56:45.0
The requirement to reconsider traditional soldering methods is becoming more relevant as the demand for bottom terminated components (QFN/BTC) increases. Thermal pads under said components are designed to enhance the thermal and electrical performance of the component and ultimately allow the component to run more efficiently. Additionally, low voiding is important in decreasing the current path of the circuit to maximize high speed and RF performances. The demand to develop smaller, more reliable, packages has seen voiding requirements decrease below 15 percent and in some instances, below 10 percent.Earlier work has demonstrated the use of micro-fluxed solder preforms as a mechanism to reduce voiding. The current work builds upon these results to focus on developing an engineered approach to void reduction in leadless components (QFN) through increasing understanding of how processing parameters and a use of custom designed micro-fluxed preforms interact. Leveraging the use of a micro-fluxed solder preform in conjunction with low voiding solder paste, stencil design, and application knowhow are critical factors in determining voiding in QFN packages. The study presented seeks to understand the vectors that can contribute to voiding such as PCB pad finish, reflow profile, reflow atmosphere, via configuration, and ultimately solder design.A collaboration between three companies consisting of solder materials supplier, a power semiconductor supplier, and an electronic assembly manufacturer worked together for an in-depth study into the effectiveness of solder preforms at reducing voiding under some of the most prevalent bottom terminated components packages. The effects of factors such as thermal pad size, finish on PCB, preform types, stencil design, reflow profile and atmosphere, have been evaluated using lead-free SAC305 low voiding solder paste and micro-fluxed preforms. Design and manufacturing rules developed from this work will be discussed.
Technical Library | 2019-12-12 02:43:44.0
Today we discuss the reason that causes temperature humidity chamber to alarm,In most cases, the equipment alarm is caused by the improper operation in the process of use, which mainly includes following reasons:that are refrigeration system, temperature system and circulating system. First, Refrigeration system 1, refrigeration compressor overpressure alarm. If the refrigerant pressure exceeds the set value, it will stop and alarm at the same time. At this time, the fault must be eliminated and then manually reset. 2, short phase power supply, phase sequence alarm. When the external power supply of the equipment is out of phase or the phase sequence is changed, it will stop and alarm at the same time. 3. The circulating cooling water is short of water to alarm. When the water pressure of the cooling circulating water system is insufficient, it will stop and alarm at the same time, and it must wait for the fault to be eliminated and reset at the same time before it could run normally. 4, refrigeration compressor overheating alarm. When the coil of the compressor is overheated and the power supply of the line is not normal, it will stop and alarm at the same time. Second, Temperature system 1, the overtemperature alarm in the chamber. The sensors in the channel and the sample area are equipped with overtemperature protection devices, and there are also overtemperature protecter on the control panel. When the temperature in the working chamber exceeds the setting value on the controller, it will stop and alarm. 2. sample overtemperature protection. When the temperature in the sample area exceeds the protection temperature set by the controller, it will stop and alarm at the same time. The overtemperature protection of the sample is divided into upper limit protection and lower limit protection, which can be set according to the demand, Third,Circulating system 1. The alarm is caused by the overheating of the circulating fan. When the coil of the fan is over-heated, the alarm will be stopped at the same time. 2. The fan over-current alarm. When the current of the fan exceeds the allowable value, the alarm is stopped at the same time, and the normal operation can only be carried out after the fault maintenance of the overcurrent is completed. This is what we talk about today,if you have more questions,let us know.
Technical Library | 2020-07-29 19:58:48.0
The majority of flexible circuits are made by patterning copper metal that is laminated to a flexible substrate, which is usually polyimide film of varying thickness. An increasingly popular method to meet the need for lower cost circuitry is the use of aluminum on Polyester (Al-PET) substrates. This material is gaining popularity and has found wide use in RFID tags, low cost LED lighting and other single-layer circuits. However, both aluminum and PET have their own constraints and require special processing to make finished circuits. Aluminum is not easy to solder components to at low temperatures and PET cannot withstand high temperatures. Soldering to these materials requires either an additional surface treatment or the use of conductive epoxy to attach components. Surface treatment of aluminum includes the likes of Electroless Nickel Immersion Gold plating (ENIG), which is extensive wet-chemistry and cost-prohibitive for mass adoption. Conductive adhesives, including Anisotropic Conductive Paste (ACP), are another alternate to soldering components. These result in component substrate interfaces that are inferior to conventional solders in terms of performance and reliability. An advanced surface treatment technology will be presented that addresses all these constraints. Once applied on Aluminum surfaces using conventional printing techniques such as screen, stencil, etc., it is cured thermally in a convection oven at low temperatures. This surface treatment is non-conductive. To attach a component, a solder bump on the component or solder printed on the treated pad is needed before placing the component. The Aluminum circuit will pass through a reflow oven, as is commonly done in PCB manufacturing. This allows for the formation of a true metal to metal bond between the solder and the aluminum on the pads. This process paves the way for large scale, low cost manufacturing of Al-PET circuits. We will also discuss details of the process used to make functional aluminum circuits, study the resultant solder-aluminum bond, shear results and SEM/ EDS analysis.
Technical Library | 2020-11-24 23:01:04.0
The miniaturization trend is driving industry to adopting low standoff components or components in cavity. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing/drying is getting very difficult for devices due to poor venting channel. This resulted in insufficiently dried/burnt-off flux residue. For a properly formulated flux, the remaining flux activity posed no issue in a dried flux residue for no-clean process. However, when venting channel is blocked, not only solvents remain, but also activators could not be burnt off. The presence of solvents allows mobility of active ingredients and the associated corrosion, thus poses a major threat to the reliability. In this work, a new halogen-free no-clean SnAgCu solder paste, 33-76-1, has been developed. This solder paste exhibited SIR value above the IPC spec 100 MΩ without any dendrite formation, even with a wet flux residue on the comb pattern. The wet flux residue was caused by covering the comb pattern with 10 mm × 10 mm glass slide during reflow and SIR testing in order to mimic the poorly vented low standoff components. The paste 33-76-1 also showed very good SMT assembly performance, including voiding of QFN and HIP resistance. The wetting ability of paste 33-76-1 was very good under nitrogen. For air reflow, 33-76-1 still matched paste C which is widely accepted by industry for air reflow process. The above good performance on both non-corrosivity with wet flux residue and robust SMT process can only be accomplished through a breakthrough in flux technology.
Technical Library | 2019-04-08 23:21:29.0
Climatest Symor® adopts molecular sieve to dry air, the whole system is controlled by microcomputer, when humidity is high, It will start to absorb moisture,when the humidity reach the pre-set value, it will stop absorbing, and then discharge the water to outside the cabinet by heating,again and again by automatic control. The most effective and environment-friendly moisture-absorbing desiccant is molecular sieve, molecular sieve is the microporous crystal material synthesized by silicon and aluminium oxide. In order to keep the crystal net discharge to be zero, atoms with cations are located in the crystal structure.and the cation used in these synthetic crystals is usually sodium. At present, there are two kinds of molecular sieves widely used in the dry box industry: Class A and Class X. Molecular sieves are synthesized, shaped and activated under strictly controlled production processes. The whole controlled sythesis process can ensure consistency of the three-dimensional pore size. 3A molecular sieve pore size is 3 angstroms, 4A molecular sieve pore size is 4 angstroms; 13X molecular sieve pore size is 8.5 angstroms. The working principle of molecular sieve: Molecular sieves adsorb molecules onto the crystal surface by physical attraction force. Since 95% surface area of the molecular sieve is within aperture,it needs to screen the adjacent molecules by different size. Only small size molecules can enter into the inner adsorption surface of the molecular sieve through the crystal aperture. This selective adsorption phenomenon is called molecular sieve effect. The molecular sieve adsorption capacity and charge density (polarity) are further related to the adsorbed molecules. The molecular sieves can further distinguish which of the mixed molecules can be adsorbed and determine to what extent the charge density can allow the molecules to be adsorbed onto the crystal. Water molecules are particularly small (2.6 angstroms), that belong to highly polar molecules (very strong positive and negative electron density), and are easily adsorbed by molecular sieves, even under very low moisture condition,once the water molecules are adsorbed,they will be firmly fixed on the crystal. The environment-friendly moisture absorption device is equipped with molecular sieve. When it’s absorbing, the memory alloy controller is in tensile state, and the spring is in contractive state,which just make the valve contact the outer baffle, this insulates the outside air from inside dry box air to achieve dehumidification purpose; and after molecular sieve absorbed moisture inside dry box and become saturated, the program will automatically control the memory alloy device to shrink it so that the valve reaches the inner baffle position. Meanwhile, due to the shrinkage of the memory alloy, the spring is stretched and the valve is pulled out of the outer baffle,so that the moisture in molecular sieve will be discharged into the outside. after the dehumidifying process finished, the program automatically control and reset the memory alloy and spring,to restart absorbing status.
Technical Library | 2019-11-15 02:20:26.0
Material Aging Test-UV Weathering Test Chamber 1.What is UV aging? UV aging chambers use fluorescent ultraviolet lamp as light source to simulate UV radiation and condensation in natural sunlight, and to carry out accelerated weather resistance test in order to obtain the result of weather resistance of the material. UV aging detection is widely used in non-metallic materials, organic materials (such as coatings, paints, rubber, plastics and their products) under the change of sunlight, humidity, temperature, condensation and other climatic conditions to test the aging degree and situation of related products and materials. 2.Why we should do UV aging test? When the product is placed in the ambient environment, there will be different problems taken place, such as appearance changes, including cracking, speckle, powdering or color change, and even performance degradation,which may be due to the loss of components in the resin resulting in chemical bonds changes inside the molecular structure, this is mainly caused by sunlight, industrial exclusion of waste gas, bacteria and so on. The aging performance of the product directly affects the lifespan of the product, so aging test become significant,non-metallic materials, organic materials (such as paints, paints, rubber, plastics and their products) are subject to changes in sunlight, humidity, temperature, condensation and other climatic conditions to test the degree and condition of aging of related products and materials. The natural aging test is to put the plastic specimen under the sun exposure, and it is directly under the natural climate environment,to test the material performance under various factors such as light, heat energy, atmospheric humidity, oxygen and ozone, industrial pollution and the like, the most harsh climate condition should be selected,or near the actual application area of the material, the test site shall be open and flat, no obstacle to affect the test results,the specimen holder shall be facing the equator and at an angle of 45 ° from the ground. When the main performance index of the specimen has been reduced, the test s/b terminated when it achieve the minimum allowable use value . in most case,the test is terminated when the product primary performance index falls to 50% of the initial value. The natural aging process is a very slow process, and there is a great difference in different geographical conditions, which brings difficulties to evaluate the aging resistance of the product. It is an attempt to make an evaluation of the aging performance of the plastic in a shorter time,that is accelerated aging test. The accelerated aging test can be used to simulate the human light source of the fluorescent lamp, including the carbon arc lamp, the xenon arc lamp and the fluorescent ultraviolet lamp, and the artificial light sources can generate more light than the natural sunlight on the ground. When these artificial light sources are used, it is also common to use the combination of the condenser to simulate the rain drop, the dew and the like to conduct the aging test on the product.
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