PCB表面绝缘性能影响因素的研究

Study on factors affecting surface insulation performance of PCB

摘要

[目的]探究印刷电路板组件(PCBA)表面绝缘性能的影响因素，明确板面离子残留浓度与三防漆厚度的作用机制，为汽车电子等领域 PCBA 的工艺控制与可靠性设计提供依据。[方法]以 IPC-B-25A 标准板为试验基板，分别采用水基型和免洗型助焊剂制备不同离子残留浓度(0.5、1.5、3.0、5.0、7.0、12.0 μg/cm ²)的试样，并在部分试样表面喷涂三防漆，获得单面厚度分别为 50、100 和 150 μm 的涂覆板。通过水滴法电化学迁移试验、交变温湿度(25 ~ 65 °C、相对湿度≥93%)下的电阻监测以及划格法涂层附着力测试，系统评估离子残留浓度和三防漆厚度对 PCB 表面绝缘性能的影响。[结果]无三防漆时，离子残留浓度超 1.5 μg/cm ² 会显著增加绝缘失效风险，水基型助焊剂比免洗型更易引发电化学迁移；涂覆三防漆后，离子残留浓度对电阻影响不显著，但会影响涂层附着力。[结论]为保障 PCB 表面绝缘性能，应优先选用免洗型助焊剂；无防护产品需将离子残留浓度控制在 1.5 μg/cm ² 以下；三防漆的厚度应根据产品可靠性寿命要求与离子残留水平综合确定，高离子残留或高可靠性场景下需采用更厚的涂层。

Abstract

[Objective]To study the factors affecting the surface insulation performance of printed circuit board assembly (PCB), clarify the action mechanisms of ionic residue concentration on the board surface and conformal coating thickness, and provide a basis for process control and reliability design of PCBA in fields such as automotive electronics. [Method] Using IPC-B-25A standard boards as test substrates, specimens with different ionic residue concentrations (0.5, 1.5, 3.0, 5.0, 7.0, 12.0 μg/cm ²) were prepared using water-based and no-clean fluxes respectively. Conformal coating was sprayed on some specimens to obtain coated boards with single-side thicknesses of 50, 100, and 150 μm. The effect of ionic residue concentration and conformal coating thickness on the surface insulation performance of PCB was systematically evaluated through water drop electrochemical migration tests, resistance monitoring under alternating temperature (25-65 °C) and at relative humidity ≥93%, and cross-cut coating adhesion tests. [Result]Before spraying conformal coating, an ionic residue concentration exceeding 1.5 μg/cm ² significantly increased the risk of insulation failure, and water-based flux was more likely to induce electrochemical migration than no-clean flux. After spraying conformal coating, the ionic residue concentration had no significant effect on resistance but affected coating adhesion. [Conclusion]To ensure the surface insulation performance of PCB, no-clean flux should be preferred; for unprotected products, the ionic residue concentration should be controlled below 1.5 μg/cm ²; the thickness of the conformal coating should be determined comprehensively based on the product’s reliability life requirements and the ionic residue concentration, and thicker coatings are required under high ionic residue or high reliability scenarios.

关键词

印刷电路板 / 离子残留浓度 / 三防漆 / 电阻 / 附着力

Key words

printed circuit board / ionic residue concentration / conformal coating / resistance / adhesion

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