SMTA International Conference Proceedings


Authors: Ranjit Pandher, Rahul Raut, Michael Liberatore, Navendra Jodhan, and Karen Tellefsen
Company: Cookson Electronics
Date Published: 10/24/2010   Conference: SMTA International

Abstract: Head-in-Pillow (HIP) defects are a growing concern in the electronics industry. These defects are usually believed to be the result of several factors, individually or in combination. Some of the major contributing factors include: surface quality of the BGA spheres, activity of the paste flux, improper placement / misalignment of the components, a non-optimal reflow profile, and warpage of the components. To understand the role of each of these factors in producing head-in-pillow defects and to find ways to mitigate them, we have developed two in-house tests.

Approach 1: In this approach a BGA rework station was used. A 35mm x 35mm, SAC305 PBGA package was placed on the test board. Rework profiles with different temperature gradients and varying solder paste formulations were used to create HIP defects. This test method showed the effect of: (i) Components, (ii) ?T across the test board and (iii) Solder paste chemistry on HIP defect.

Approach 2: In this approach a custom designed test set-up was used to place a single SAC305 solder sphere on a molten lead-free solder paste deposit. Spheres were placed at different times and temperatures to create varying HIP defect rates. This test method showed the effect of: (i) Sphere oxidation, (ii) Reflow profiles and (iii) Solder paste chemistries on HIP. Further, a detailed comparative study of a number of lead-free solder pastes was also completed.

Conclusions from these test methods are detailed herein. In particular, the focus was on the experiments run to understand the critical role of the flux chemistry on HIP defects. Initial results show that the paste flux chemistry plays an important role in producing and mitigating HIP defects. A quantitative comparison of the paste performance is also presented. In addition, the role of the reflow profile optimization for each of the pastes will be discussed. The main objective of this paper thus is to identify the root causes of the HIP defect and to investigate potential material and process solutions to minimize HIP.

Key words: Lead-free assembly, Head-in-pillow defect, process optimization, solder paste activity, oxidation (of BGA spheres) and BGA warpage.

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