Technical Library | 2019-07-23 22:33:47.0
The Quad Flat Pack No Leads (QFN) style of leadless packaging [also known as a Land Grid Array (LGA)] is rapidly increasing in us e for wireless, automotive, telecom and many other areas becaus e of its low cost, low stand-off height and excellent thermal and electri cal properties. With the implementation of any new package type, there is always a learning curve for its use in design and processing as well as for the Process and Quality Engineers who have to get to grips with the challenges that these packages bring. Therefore, this paper will provide examples of the common process defects that can be seen with QFNs /LGAs when using optical and x-ray inspection as part of manufacturing quality control. Results of trials conducted on four PCB finishes and using vapour phase and convection reflow will be discussed.
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 | 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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