The circuit board is getting hairy, what's the cause?

Jenny Lee: The circuit board is hairy. The area did not do conformal coating, temperature cycle experiment, -40 ~ +60 ℃, 5 times

Zhu Jia Cheng: did not apply the conformal coating, why solder wire one by one?@ Zhen Zhen Li

Li Zhenzhen: Yes, that area is the test wire, to be desoldered, did not do conformal coating@Zhu Jiacheng

Wen Nengwu: the shot is not clear, can not see whether it is mould or corrosion @Jenny Lee

ZhenZhen Li: There are black and white things growing out, the centre is black, the back of the board is not, it looks like it is not from the root of the wire growing out of no conformal coating, spreading to the surrounding area @Wen Nengwu

Wang Hao: moisture condensation + board surface residue, too many rings, residue should not be easily determined @Jenny Lee

Jenny Lee: It should be flux, can this ingredient be identified?

Liu Haiguang: If it is fungal, 40~50 hot air will shrink and disappear, the white spots of flux emulsification by moisture will continue to exist , see if there is creep corrosion, crystalline @ Jenny Lee

Jenny Lee: Okay, let's see, What is creep corrosion?

Liu Haiguang: crystalline direction of the dendrite (electric field + moisture), no direction of the creep corrosion (only moisture-related) two diagrams of the former creep corrosion, the latter is the migration of ions under the dendrite

Jenny Lee: OK, got it, let's take a look, thank you Mr Liu

Liu haiguang: bacteria is unlikely, the environment is not suitable @ Jenny Lee

Zhang Yongzhong: the probability is that the solder and moisture related to the humidity is now large temperature cycle low temperature will be condensation

Jenny Lee: Liu, the first picture of the two metallographic, the left side is creep, the right side is dendrite, right? The physical appearance of the picture is also the left and right corresponds to the right and left @ Liu Haiguang

Liu Haiguang: The dendrite situation is very interesting, the phenomenon of half a month's service under the conformal coating, that picture is all creep corrosion, only the other one has been tampered with, silver PCB, electron microscope magnification, conformal coating after the dendrites indicate that the degree of cleanliness is not enough, there is ionic contamination @Jenny Lee

Jenny Lee: Well, thank you Mr Liu, creep is also the first pollution and then moisture lead to it? The reason is not clean enough?

Liu haiguang: right, huawei article there are hints of pollution ion category @Jenny Lee - Times Optoelectronics