Technical Library | 2018-09-21 10:12:53.0
Moisture accumulates during storage and industry practice recommends specific levels of baking to avoid delamination. This paper will discuss the use of capacitance measurements to follow the absorption and desorption behaviour of moisture. The PCB design used in this work, focused on the issue of baking out moisture trapped between copper planes. The PCB was designed with different densities of plated through holes and drilled holes in external copper planes, with capacitance sensors located on the inner layers. For trapped volumes between copper planes, the distance between holes proved to be critical in affecting the desorption rate. For fully saturated PCBs, the desorption time at elevated temperatures was observed to be in the order of hundreds of hours. Finite difference diffusion modelling was carried out for moisture desorption behaviour for plated through holes and drilled holes in copper planes. A meshed copper plane was also modelled evaluating its effectiveness for assisting moisture removal and decreasing bake times. Results also showed, that in certain circumstances, regions of the PCB under copper planes initially increase in moisture during baking.
Technical Library | 2019-01-09 19:19:52.0
The electronics industry has widely adopted Sn-3.0Ag-0.5Cu solder alloys for lead-free reflow soldering applications and tin-copper based alloys for wave soldering applications. In automated soldering or rework operations, users may work with Sn-Ag-Cu or Sn-Cu based alloys. One of the challenges with these types of lead-free alloys for automated / hand soldering operations, is that the life of the soldering iron tips will shorten drastically using lead-free solders with an increased cost of soldering iron tool maintenance/ tip replacement. Development was done on a new lead-free low silver solder rework alloy (Sn-0.3Ag-0.7Cu-0.04Co) in comparison with a number of alternative lead-free alloys including Sn-0.3Ag-0.7Cu, Sn-0.7Cu and Sn-3.0Ag-0.5Cu and tin-lead Sn40Pb solder in soldering evaluations.
Technical Library | 2019-05-06 23:04:05.0
The temperature and humidity test chamber simulate the temperature and humidity, so there are a lot of things customers shoud notice in the process of use, although there is detailed instruction when purchasing the equipment. But some users just know how the device works and start using it. This is very easy to cause problems in the use of the equipment, so Symor intends to describe the safety details during the use of temperature and humidity chamber. 1. Before the test, determine if the sample contains flammable and explosive substances to avoid combustion or explosion during the test. Of course, also make sure there is no flammable and explosive material around the test equipment, otherwise it may cause fire and other accidents. 2, Do not open the chamber door to operate during the experiment, or the gas in the studio may cause the operator to burn and so on. 3. At the end of the test or at the time of regular cleaning of the test chamber, power off the equipment to avoid electrocution accidents. Also, when cutting off the equipment power, pull the power cord to pull out the plug, otherwise it may lead to a rupture of the power cord and so on. You can contact manufacturers if there are some places you donnot understand, do not dismantle and repair the temperature and humidity test chamber without authorization, otherwise it may lead to more serious problems.
Technical Library | 2019-10-10 00:26:28.0
Voids are a plague to our electronics and must be eliminated! Over the last few years we have studied voiding in solder joints and published three technical papers on methods to "Fill the Void." This paper is part four of this series. The focus of this work is to mitigate voids for via in pad circuit board designs. Via holes in Quad Flat No-Lead (QFN) thermal pads create voiding issues. Gasses can come out of via holes and rise into the solder joint creating voids. Solder can also flow down into the via holes creating gaps in the solder joint. One method of preventing this is via plugging. Via holes can be plugged, capped, or left open. These via plugging options were compared and contrasted to each other with respect to voiding. Another method of minimizing voiding is through solder paste stencil design. Solder paste can be printed around the via holes with gas escape routes. This prevents gasses from via holes from being trapped in the solder joint. Several stencil designs were tested and voiding performance compared and contrasted. In many cases voiding will be reduced only if a combination of mitigation strategies are used. Recommendations for combinations of via hole plugging and stencil design are given. The aim of this paper is to help the reader to "Fill the Void."
Technical Library | 2022-09-12 14:07:47.0
Unique component handling issues can arise when an assembly factory uses highly-moisture sensitive surface mount devices (SMDs). This work describes how the distribution of moisture within the molded plastic body of a SMD is an important variable for survivability. JEDEC/IPC [1] moisture level rated packages classified as Levels 4-5a are shown to require additional handling constraints beyond the typical out-of-bag exposure time tracking. Nitrogen or desiccated cabinet containment is shown as a safe and effective means for long-term storage provided the effects of prior out-of-bag exposure conditions are taken into account. Moisture diffusion analyses coupled with experimental verification studies show that time in storage is as important a variable as floor-life exposure for highly-moisture sensitive devices. Improvements in floor-life survivability can be obtained by a handling procedure that includes cyclic storage in low humidity containment. SMDs that have exceeded their floor-life limits are analyzed for proper baking schedules. Optimized baking schedules can be adopted depending on a knowledge of the exposure conditions and the moisture sensitivity level of the device.
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 | 2022-12-05 16:28:06.0
The work evaluates the impact of latent heat (LH) absorbed or released by a solder alloy during melting or solidification, respectively, on changes of dimensions of materials surrounding of the solder alloy. Our sample comprises a small printed circuit board (PCB) with a blind via filled with lead-free alloy SAC305. Differential scanning calorimetry (DSC) was employed to obtain the amount of LH per mass and a thermomechanical analyzer was used to measure the thermally induced deformation. A plateau during melting and a peak during solidification were detected during the course of dimension change. The peak height reached 1.6 μm in the place of the heat source and 0.3 μm in the distance of 3 mm from the source. The data measured during solidification was compared to a numerical model based on the finite element method. An excellent quantitative agreement was observed which confirms that the transient expansion of PCB during cooling can be explained by the release of LH from the solder alloy during solidification. Our results have important implications for the design of PCB assemblies where the contribution of recalescence to thermal stress can lead to solder joint failure.
Technical Library | 2019-03-15 16:26:50.0
While there have been quite dramatic and evident improvements in almost every facet of manufacturing over the last several decades owing to the advent and mass adoption of computer automation and networking, there is one aspect of production that remains stubbornly unaffected. Massive databases track everything from orders, to inventory, to personnel. CAD systems allow for interactive and dynamic 3D rendering and testing, digital troubleshooting, and simulation and analysis prior to mass production. Yet, with all of this computational power and all of this networking capability, one element of production has remained thoroughly and firmly planted in the past. Nearly all manufacturing or assembly procedures are created, deployed, and stored using methodologies derived from a set of assumptions that ceased to be relevant fifty years ago. This set of assumptions, referred to below as the “Paper Paradigm” has been, and continues as the dominant paradigm for manufacturing procedures to this day. It is time for a new paradigm, one that accounts for the vastly different technological landscape of this era, one that provides a simple, efficient interface, deep traceability, and dynamic response to rapidly changing economic forces.This paper seeks to present an alternative. Instead of enhancing and improving on systems that became irrelevant with the invention of a database, instead of propping up an outdated, outmoded and inefficient system with incremental improvements; rewrite the paradigm. Change the underlying assertions to more accurately reflect our current technological capability. Instead of relying on evolutionary improvements, it is time for a revolution in manufacturing instructions.
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 | 2016-04-14 13:49:44.0
A system level test, usually built-in test (BIT), determines that one or more subsystems are faulty. These subsystems sent to the depot or factory repair facility, called units under test (UUTs) often pass that test, an event we call No-Fault-Found (NFF). With more-and more electronics monitored by BIT, it is more likely that an intermittent glitch will trigger a call for a maintenance action resulting in NFF. NFFs are often confused with false alarm (FA), cannot duplicate (CNDs)or retest OK (RTOK) events. NFFs at the depot are caused by FAs, CNDs, RTOKs as well as a number of other complications. Attempting to repair NFF scan waste precious resources, compromise confidence in the product, create customer dissatisfaction, and the repair quality remains a mystery. The problem is compounded by previous work showing that most failure indications calling for repair action at the system level are invalid. NFFs can be caused by real failures or may be a result of system level false alarms. Understanding the cause of the problem may help us distinguish between units under test (UUTs) that we can repair and those that we cannot. In calculating the true cost of repair we must account for wasted effort in attempting to repair unrepairable UUTs.This paper will shed some light on this trade-off. Finally, we will explore approaches for dealing with the NFF issue in a cost effective manner.
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