J Fail. Anal. and Preven.(2008)8: 524-532 main cause of failure. The analytical results show that it is T=323℃ the defect of the blind vias that leads to the open circuits. a big open cracking from one side of the blind via with result of a separation completely between the pad and the copper-plating layer is shown in Fig. 6. An obviou cracking from the bottom of the other blind via that partly separated the via and the copper foil is presented in Fig. 7 We can also notice from the location of these two blind vias that the design position between pads and blind vias is somewhat improper. They are not kept in the same Z-direction. and the distance between them is too small Usually, the region close packed with deep color T℃ temperature around the pads covered with solder of color rises faster than pad areas without solder during the heating for reflow soldering; while temperature in the areas T=322℃ with just the pads drops faster than in those overlaid with solder in the cooling segment of reflow soldering. The mismatch CtE of these two areas results in a strong ther mal stress and ric defor the blind via linked closely to the pad uncovered with solder. Accord ingly, the improper circuit design regarding the location of blind vias and pads is the leading cause of vias cracking In addition, the eds results(Fig. 6c and 7c) demon- strate that a certain amount of sulfur which usually leads to embrittlement concentrates at the interface. higher mag- cifications of the cracking and many microcracks can be in Fig. 7(d)g). These grains near cracking has also been obtained by FlB, with a ig. 3 TGA curve of bare board. (a) Type I(b) Type 2 sound characteristic of intercrystalline fracture. It can be Fig 4(a)Location of the via(type 1). b) Appearance of the vi 4.5x(c) and(d) Cracking by 3D and OM. a d 2 Springmain cause of failure. The analytical results show that it is the defect of the blind vias that leads to the open circuits. A big open cracking from one side of the blind via with a result of a separation completely between the pad and the copper-plating layer is shown in Fig. 6. An obvious cracking from the bottom of the other blind via that partly separated the via and the copper foil is presented in Fig. 7. We can also notice from the location of these two blind vias that the design position between pads and blind vias is somewhat improper. They are not kept in the same Z-direction, and the distance between them is too small. Usually, the region close packed with deep color dots shows a comparatively faster rate of heating. Therefore, temperature around the pads covered with solder of dark color rises faster than pad areas without solder during the heating for reflow soldering; while temperature in the areas with just the pads drops faster than in those overlaid with solder in the cooling segment of reflow soldering. The mismatch CTE of these two areas results in a strong ther￾mal stress and an asymmetric deformation in the blind vias linked closely to the pad uncovered with solder. Accord￾ingly, the improper circuit design regarding the location of blind vias and pads is the leading cause of vias cracking. In addition, the EDS results (Fig. 6c and 7c) demon￾strate that a certain amount of sulfur which usually leads to embrittlement concentrates at the interface. Higher mag￾nifications of the cracking and many microcracks can be seen in Fig. 7(d)–(g). These microcracks are generated along the deposited copper grains. Microstructure of the grains near cracking has also been obtained by FIB, with a sound characteristic of intercrystalline fracture. It can be Fig.4 (a) Location of the failure blind via (type 1). (b) Appearance of the via. 4.59 (c) and (d) Cracking morphologies by 3D and OM. 409 and 609 Fig. 3 TGA curve of bare board. (a) Type 1. (b) Type 2 J Fail. Anal. and Preven. (2008) 8:524–532 527 123