ICSR (Soldering and Reliability) Conference Proceedings

IPC-CC-830B vs The Real World: Part 3. Factors Influencing the Tendency for A Conformal Coating to Crack During Thermal Shock Cycling

Authors: Carolyn Taylor, Emma Mangham, and Phil Kinner
Company: Electrolube Ltd
Date Published: 5/19/2015   Conference: ICSR (Soldering and Reliability)

Abstract: As electronics continue to become ever more densely populated, and expected to operate in ever more hostile environments, the use of conformal coating is becoming more and more essential to protect the assembly from its operating environment, and ensure acceptable reliability for the application intended.

Conformal coated assemblies are often exposed to harsh operating environments, including high humidity, high temperatures, corrosive gases, condensing environments and rapid changes in operating temperature.

It is important that the conformal coating can withstand its anticipated operating environment. In parts 1 and 2 of this paper, populated SIR test assemblies were subjected to a harsh sequential load and their ability to withstand corrosion was assessed by SIR. Several of the coatings tested cracked during thermal shock testing, and once the integrity of the protective coating was destroyed, corrosion was more evident than on coatings that did not crack.

In this paper, Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used in conjunction with Tensile Testing to characterise a variety of materials that had previously been subjected to the test regime devised in parts 1 and 2 of this paper to better understand the influence of various material properties on the tendency to crack during thermal shock excursions, a key factor in the overall protective capability of a conformal coating. A direct correlation between the tensile properties of the coating after thermal ageing and cycles to thermal shock failure was determined suggesting that the high temperature extreme was as great an issue if not more so than the low storage extreme.

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