Powder standard sieves apertures

There are several single-particle characteristics that are very important to product properties (Davies, 1984). They include particle size, particle shape, surface, density, hardness, adsorption properties, and so on. From all these mentioned features, particle size is the most essential and important one. The term "size" of a powder or particulate material is very relative. It is often used to classify, categorize, or characterize a powder, but even the term powder is not clearly defined and the common convention considers that for a particulate material to be considered powder, its approximate median size (50% of the material is smaller than the median size and 50% is larger) should be less than 1 mm. It is also common practice to talk about "fine" and "coarse" powders several attempts have been made at standardizing particle nomenclature in certain fields. For example. Table 1.1 shows the terms recommended by the British Pharmacopoeia referred to standard sieves apertures. Also, by convention, particle sizes may be expressed in different units depending on the size range involved. Coarse particles may be measured in centimeters or... 

Table 9 shows the results of the sieve analysis obtained for a sample of a FCC1 powder. The values reported in the first two columns of the table are the standard diameters of the sieve apertures. From these the mean diameter dp is obtained for each two adjacent sieve sizes and the values are reported in the third column. From the mass fraction of powder in each sieve (values in the fourth column) the weight percentage is obtained and reported in the fifth column. Thus, the sum of the mass fraction over the mean diameter allows the calculation of the volume-surface mean particle diameter of the distribution using Equation (1) ... 

Such sieves were used solely for powder classification, and the inception of test sieving did not arise until sieve aperture sizes were standardized. Standard apertures were first proposed by Rittinger [2] who, in 1867, suggested a V2 progression of aperture sizes based on 75 pm thus, similarly shaped particles passing consecutive apertures, are in a 2 1 surface ratio. Modem standards are based on a fourth root of two progression, apart from the French AFNOR series, adopted in 1938, which is based on a sieve aperture of 1 mm in a tenth root of ten progression this is known as the RIO or Renaud series. 

The size of the particles in a solder paste determines the print characteristics, amongst other things. The particles are produced by a variety of methods, but they are most commonly made by dispersion of a stream of molten solder onto a rotating disk. The particles fall into a tank filled with an inert atmosphere where they solidify and then are collected at the bottom of the chamber. The collected particles are separated by size utilizing in a series of wire-mesh sieves. The mesh size is typically given in wires or holes per square inch. The Joint Industry Standard, J-STD-005, provides for solder paste particle size classification as listed in Table 1. The choice of solder-powder particle size for SMT applications is based on component pitch, part mix and pad arrangement. For example, the paste particle size required for an area array device is smaller compared to a peripheral-leaded device with the same pitch. A 0.5-mm pitch area array device may have 0.25-mm diameter pads which require a 0.25-mm to 0.3-mm stencil aperture to print a Type rv solder paste with an approximately at 60-80% transfer efficiency. Comparatively, a 0.5— mm pitch quad flat pack device would typically have an 0.2 mm to 0.2.5mm wide pad, but require a 0.15 to 0.2mm wide stencil aperture to print a Type III paste with approximately a 80 90% efficiency. 

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