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42 SMT Magazine • August 2015 ments were measured over the entire tempera- ture range of a reflow profile, including room temperature. For the discussion of this paper and to the interests of the authors, the dynam- ic warpage zone corresponding to the reflow profile is defined as the zone between 150°C to the maximum temperature of a profile (i.e., 260°C for a small BGA and 245°C for a large BGA). In both standards, positive warpage is de- scribed as convex whereas negative warpage is described as concave as shown in Figure 6. Figure 7 and 8 show the current acceptable warpage by ball diameter, height and package pitch as a reference for the discussion of this paper. Again, the discussion and proposed ac- ceptance is limited to BGA components with a pitch of 0.8 mm and above. The JEITA and JEDEC specifications are structured differently and have a maximum al- lowable warpage based on pitch, size, etc. Using the most common 1 mm pitch BGA as a com- parison, the JEITA standard allows up to 0.22 mm (8.6 mil) warpage regardless of the size of figure 5: Hop defect escape hypothesis, illustrated. figure 6: Description of the warpage shapes. WARPAGE ACCEPTANCE PROPOSAL continues FeAture