Statistical Study on the Characteristics and Thermal Quality of Solder Voids in Automotive LEDs

Purpose: This study statistically analyzed solder void characteristics and their thermal effects in automotive LEDs to better understand void behavior and contribute to establishing acceptance criteria and process control guidelines.Methods: Solder coverage and void ratios were evaluated using X-ray inspection and ImageJ analysis. Process capability was statistically assessed through normality and <i>C<sub>pk</sub></i> analysis. Voids were classified into macro- and micro-types. Thermal quality was examined via <i>Z<sub>th</sub>(t)</i> and structure function <i>a(z)</i> , with Pearson correlation, Mutual Information, and Hoeffding’s D applied. The relationship between solder voids and LED temperature rise (∆<i>T<sub>s</sub></i> ) was also analyzed under production-equivalent measurement conditions.Results: Solder coverage showed <i>C<sub>pk</sub></i>> 1, with all void ratios below 25%, confirming process capability. Pad size influenced void distribution, peaking at an intermediate size before declining with further enlargement. Thermal pad voids and macrovoids were the main contributors, showing weak but consistent correlations with <i>Z<sub>th</sub>(t)</i> and <i>a(z)</i> . No significant correlation was found between voids and ∆<i>T<sub>s</sub></i> , indicating negligible thermal impact within the IPC 25% limit.Conclusion: It is more effective to control voids in specific pads and macrovoids rather than pursuing uniform minimization. Establishing tailored void management standards that reflect product structures and operating environments can guide automotive LED manufacturers in process design. Since this study did not include void levels beyond the 25% limit, extended research is required.