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34 SMT007 MAGAZINE I JULY 2019 an effect on solder paste performance. Solder powder sizes are classified by type in the IPC standard J-STD-005 (requirements for solder- ing pastes) [1] . Table 3-2 details the solder pow- der size ranges for each type, and an excerpt is shown in Table 1. The main particle size range is normally associated with the type. For example, Type 3 solder powder mainly falls within the 25–45 μm size range; therefore, Type 3 solder paste may be labeled as "Type 3 (25–45 μm)." Fig- ure 2 shows Type 3, 4, 5, and 6 sizes of solder powder. Why use Type 4, 5, or 6 solder powder rather than Type 3? The main reason to use smaller solder powders in solder paste is to improve the printability for miniature components. As solder powder size decreases, the solder pastes can be printed through smaller stencil aper- tures. If the "5-ball" rule is followed from the IPC-7525 stencil design guidelines standard [2] , then the minimum aperture size through which printing can occur can be calculated for each solder powder size [3] . These calculations for minimum aperture size were performed using five times the maximum solder powder size of the main range (Table 2). Generally speaking, Type 3 solder paste can be used for components ranging down to the 0402 imperial package size. Most solder paste users prefer Type 4 solder paste for 0201 impe- rial, micro BGAs, and similar components. Type 5 solder paste is used for even smaller sol- dering applications like 01005 imperial compo- nents [4] or when Type 4 solder paste does not print adequately. Type 5 and 6 solder pastes Table 1: Solder powder size (adapted from Table 3-2 of IPC J-STD-005A). Figure 2: IPC Type 3, 4, 5, and 6 solder powders. Table 2: Solder powder size and minimum stencil aperture size for printing using the 5-ball rule.

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