Technical Library | 2016-09-01 16:21:11.0
Sn3.0Ag0.5Cu (SAC305) is currently the most popular near eutectic lead-free alloy used in the manufacturing processes. Over the last several years, the price of silver has dramatically increased driving a desire for lower silver alloy alternatives. As a result, there is a significant increase in the number of alternative low/no silver lead-free solder alloys available in the industry recently. Our previous study showed that many alternative low silver solder paste materials had good printing and wetting performance as compared to SAC305 solder pastes. However, there is lack of information on the reliability of alternative alloy solder joints assembled using alternative low silver alloy solder pastes.In this paper, we will present the reliability study of lead-free solder joints reflowed using various lead-free alloy solder pastes after thermal cycling test (3000 cycles, 0°C to 100°C). Six different lead-free pastes were investigated. SAC305 solder joints were used as the control. Low and no silver solder pastes and a low temperature SnBiAg solder pastes were also included.
Technical Library | 2019-05-01 23:18:27.0
Moisture can accelerate various failure mechanisms in printed circuit board assemblies. Moisture can be initially present in the epoxy glass prepreg, absorbed during the wet processes in printed circuit board manufacturing, or diffuse into the printed circuit board during storage. Moisture can reside in the resin, resin/glass interfaces, and micro-cracks or voids due to defects. Higher reflow temperatures associated with lead-free processing increase the vapor pressure, which can lead to higher amounts of moisture uptake compared to eutectic tin-lead reflow processes. In addition to cohesive or adhesive failures within the printed circuit board that lead to cracking and delamination, moisture can also lead to the creation of low impedance paths due to metal migration, interfacial degradation resulting in conductive filament formation, and changes in dimensional stability. Studies have shown that moisture can also reduce the glass-transition temperature and increase the dielectric constant, leading to a reduction in circuit switching speeds and an increase in propagation delay times. This paper provides an overview of printed circuit board fabrication, followed by a brief discussion of moisture diffusion processes, governing models, and dependent variables. We then present guidelines for printed circuit board handling and storage during various stages of production and fabrication so as to mitigate moisture-induced failures.
Technical Library | 2019-05-21 00:21:26.0
Continue to talk about the dust removal from temperature humidity test chamber. Cleaning and maintenance: 1) Pls remove internal impurities inisde chamber before operation. 2) The power distribution room should be cleaned at least once a year, and the dust can be removed by vacuum cleaner. 3) The exterior chamber must also be cleaned more than once a year, which can be wiped with soapy water. Inspection and maintenance of humidifier: The water storage in humidifier should be replaced once a month to ensure clean water quality, humidifying water tray should be cleaned once a month to ensure smooth flow of water. The inspection of over-temperature protector:during the test: If the temperature is over 20 ℃ ~ 30 ℃ than the maximum value setted,the power supply of the heater will stop, the "OVERHEAT" overt-emperature warning light will automatically turn on but the fan is still in operation, if the equipment runs without operator around,the operator should check the over-temperature protector in advance to ensure wether it has been setted properly before start [wet ball over-temperature protector set to 120 ℃].
Technical Library | 2022-10-31 17:25:37.0
Mixed formulation solder alloys refer to specific combinations of Sn-37Pb and SAC305 (96.5Sn–3.0Ag–0.5Cu). They present a solution for the interim period before Pb-free electronic assemblies are universally accepted. In this work, the surfaces of mixed formulation solder alloys have been studied by in situ and real-time Auger electron spectroscopy as a function of temperature as the alloys are raised above the melting point. With increasing temperature, there is a growing fraction of low-level, bulk contaminants that segregate to the alloy surfaces. In particular, the amount of surface C is nearly _50–60 at. % C at the melting point. The segregating impurities inhibit solderability by providing a blocking layer to reaction between the alloy and substrate. A similar phenomenon has been observed over a wide range of (SAC and non-SAC) alloys synthesized by a variety of techniques. That solder alloy surfaces at melting have a radically different composition from the bulk uncovers a key variable that helps to explain the wide variability in contact angles reported in previous studies of wetting and adhesion. VC 2011 American Vacuum Society. [DOI: 10.1116/1.3584821]
Technical Library | 2023-07-25 16:50:02.0
Some of the new handheld communication devices offer real challenges to the paste printing process. Normally, there are very small devices like 01005 chip components as well as 0.3 mm pitch uBGA along with other devices that require higher deposits of solder paste. Surface mount connectors or RF shields with coplanarity issues fall into this category. Aperture sizes for the small devices require a stencil thickness in the 50 to 75 um (2-3 mils) range for effective paste transfer whereas the RF shield and SMT connector would like at least 150 um (6 mils) paste height. Spacing is too small to use normal step stencils. This paper will explore a different type of step stencil for this application; a "Two-Print Stencil Process" step stencil. Here is a brief description of a "Two-Print Stencil Process". A 50 to 75 um (2-3 mils) stencil is used to print solder paste for the 01005, 0.3 mm pitch uBGA and other fine pitch components. While this paste is still wet a second in-line stencil printer is used to print all other components using a second thicker stencil. This second stencil has relief pockets on the contact side of the stencil any paste was printed with the first stencil. Design guidelines for minimum keep-out distances between the relief step, the fine pitch apertures, and the RF Shields apertures as well relief pocket height clearance of the paste printed by the first print stencil will be provided.
Technical Library | 2019-11-17 22:46:45.0
Overview of walk-in temperature and humidity chamber: It also belongs to environmental test equipment, it tests whether the product can resist high temperature, low temperature, humidity, or the physical and chemical changes produced under extreme conditions, the walk-in temperature and humidity chamber volume is large, the product is placed, or a large object can be placed, such as automobile, new energy, television and liquid crystal screen, etc. How to do the routine maintenance of the walk-in temperature and humidity chamber: 1. The wet gauze basically, if there is no special case, s/b usually changed once in 3 months 2. The water channel shall be regularly cleaned, including water cup, water tank, etc., so as to prevent the water from being blocked,affect the humidity test. 3. It is forbidden to test the flammable and explosive products inside working room. 4. Clean the chamber on a regular basis 2. How to operate walk-in temperature and humidity chamber: The operation method is same as standard temperature humidity test chamber,the controller is 7-inch LCD programmable color screen, you only need to setthe temperature point---test time--how many cycles need to be tested, This can be done automatically, and the machine will stop automatically when it is complete. If there is any problem during the operation, the corresponding problem point will be displayed on the machine control screen. Walk-in temperature and humidity chamber is a must equipment for reliability test of Automobile,Aerospace,Electronic parts,etc,the operation and maintenance are easy,it is teh tear down mahcine,Climatest engineers will be dispatched to do on-site support,for instance,we will finish commissioning,train customers how to operate,maintain,welcome to follow our company facebook page:https://www.facebook.com/Climatechambers
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 | 2021-09-29 13:35:21.0
In PCB circuit assemblies the trend is moving to more SMD components with finer pitch connections. The majority of the assemblies still have a small amount of through hole (THT) components. Some of them can't withstand high reflow temperatures, while others are there because of their mechanical robustness. In automotive applications these THT components are also present. Many products for cars, including steering units, radio and navigation, and air compressors also use THT technology to connect board-to-board, PCB's to metal shields or housings out of plastic or even aluminium. This is not a simple 2D plain soldering technology, as it requires handling, efficient thermal heating and handling of heavy (up to 10 kg) parts. Soldering technology becomes more 3D where connections have to be made on different levels. For this technology robots using solder wire fail because of the spattering of the flux in the wires and the long cycle time. In wave soldering using pallets the wave height is limited and pin in paste reflow is only a 2D application with space limitations. Selective soldering using dedicated plates with nozzles on the solder area is the preferred way to make these connections. All joints can be soldered in one dip resulting in short cycle times. Additional soldering on a small select nozzle can make the system even more flexible. The soldering can only be successful when there is enough thermal heat in the assembly before the solder touches the board. A forced convection preheat is a must for many applications to bring enough heat into the metal and board materials. The challenge in a dip soldering process is to get a sufficient hole fill without bridging and minimize the number of solder balls. A new cover was designed to improve the nitrogen environment. Reducing oxygen levels benefits the wetting, but increases the risk for solder balling. Previous investigations showed that solder balling can be minimized by selecting proper materials for solder resist and flux.
