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Low Oil Bleed Thermal Paste for Automotive Electronics: Hanast Case Study on ECU and ADAS Camera Reliability

2026-11-09

Project Background

An automotive electronics manufacturer supplying ADAS camera modules and engine control units (ECUs) to European and Southeast Asian vehicle platforms ran into a field-return problem that no datasheet had predicted. After 12 to 18 months in service, a small percentage of camera modules showed a hazy film on the inside of the lens barrel, degrading image contrast and triggering intermittent calibration warnings.

Root cause analysis traced the haze to silicone oil migration. The thermal paste used between the image processor and the aluminium housing had an oil bleed value of 4.1% at 200 °C. Under under-hood temperatures of 105-125 °C and continuous vibration, free silicone oil crept along the housing wall and condensed on the optical surface. The same mechanism was raising contact resistance on ECU power stages, where migrated oil combined with dust to create insulating films on connector pins.

Customer Requirement Summary

Oil bleed below 1.0% at 200 °C and low volatile content
No visible fogging on optical surfaces after 1,000 h at 125 °C
Thermal conductivity of at least 1.5 W/mK to keep the image processor under 105 °C
Soft, compliant interface that survives vibration without cracking or separating
Non-curing behaviour for rework-friendly assembly and field serviceability
Full PPAP documentation, IMDS entry and IATF 16949 aligned quality records

Solution: HNS-TG150L Low Bleed Thermal Paste

Hanast developed the HNS-TG150L as a low-bleed variant of its standard thermal paste platform. The formulation uses a high-viscosity phenyl silicone carrier with a refined filler size distribution, which keeps the low molecular weight siloxane fraction to a minimum. The result is a paste that still wets the surfaces properly at low mounting pressure but releases almost no free oil over time.

Property	Test Method	Incumbent paste	HNS-TG150L
Thermal conductivity	ASTM D5470	1.6 W/mK	1.5 W/mK
Oil bleed, 24 h at 200 °C	FTMS 791 Method 321	4.1%	0.6%
Evaporation, 24 h at 200 °C	FTMS 791 Method 321	1.8%	0.3%
Low molecular siloxane (D4-D10)	GC-MS	> 900 ppm	< 150 ppm
Thermal impedance at 75 µm BLT	ASTM D5470	0.38 °C·cm²/W	0.41 °C·cm²/W
Operating range	TGA	-40 °C to 180 °C	-45 °C to 200 °C

Validation and Qualification Programme

Fogging test: Coated glass slides were placed 3 mm from the paste and aged for 1,000 h at 125 °C. The incumbent paste produced a measurable film; HNS-TG150L showed no visible deposit under 500 lux inspection.
Thermal cycling: 1,000 cycles from -40 °C to 125 °C with thermal impedance logged every 100 cycles. Impedance drift stayed within 5%.
Vibration: Random vibration at 10-2,000 Hz, 7.7 g RMS per ISO 16750-3, with no separation or cracking observed in cross-sections.
Connector compatibility: Migrated-oil effect on gold-plated connector pins was evaluated by contact resistance measurement after 500 h at 105 °C. Resistance change was below 2 mΩ.
Production validation: Three pilot lots were PPAP-approved, with IMDS entries filed for all ingredients.

Results

Metric	Before	After HNS-TG150L
Field returns due to lens fogging	0.7% of units	0 reported in 18 months
Image processor temperature at 85 °C ambient	103 °C	102 °C
Oil bleed at 200 °C	4.1%	0.6%
Connector contact resistance drift	Up to 6 mΩ	< 2 mΩ

Commercial Outcome

The customer closed a supplier corrective action that had been open for two quarters and avoided a potential recall campaign covering roughly 120,000 camera modules.
HNS-TG150L was released as the standard thermal interface for both the ADAS camera line and the ECU power-stage assembly.
Annual volume reached 2.6 tonnes, supplied from Hanast's Shenzhen plant with 4-week lead time and local stock in Southeast Asia.

Design Lesson for Automotive Electronics

Oil bleed is usually treated as a secondary specification, yet in sealed optical or high-impedance assemblies it is the specification that decides field reliability. Thermal conductivity differences of 0.1 W/mK rarely change a junction temperature more than one or two degrees, while an oil bleed difference of 3.5 percentage points can determine whether a camera module fogs up in year two. For automotive electronics buyers, the practical rule is to select thermal interface materials by end-use risk, not by conductivity ranking alone.

About Hanast

Shenzhen Hanast New Material Co., Ltd. has produced RTV-2 liquid silicone, potting compounds and thermal interface materials since 2010 from a 40,000 m² facility, exporting 70-80% of output. Customers include ABB, Apple, Google, Foxconn, ZTE and BYD. Hanast supports automotive and industrial buyers with custom formulation, low-bleed and low-volatile material development, PPAP documentation and OEM/ODM private labelling.