发表于: 2019-7-1 12:26:41 | 只看该作者 |只看大图 |倒序浏览

? ? 大家一起来讨论下,我们目前的热界面材料基本都是通过点胶机点在界面上的,不过这会带来应力问题,不知道大家知道英飞凌的丝网印刷技术不,全名叫做screen printing process ,效果看起来非常棒,界面非常均匀,整体厚度在0.05~0.1mm 厚。

?? 6 Application of the thermal interface material
Due to the individual surface shapes of the module base plates and the heat sinks, there are inherent air gaps in-between both mating surfaces. To dissipate the losses in the module and to achieve an efficient heat flow from the chip into the heat sink, these gaps or cavities must be filled by a thermal interface material (TIM). An optimum layer thickness displaces all air, but also does not prevent the metal-to-metal contact between the baseplate and the heat sink surface where it occurs.
When using a thermal conductive paste (TCP), a homogenous application has to be ensured.
A TIM should be selected that shows permanent elastic features in order to ensure a constant good heat transfer resistance. The TIM should be applied in a way that no screw holes are contaminated so that screw torqueses are not compromised.
6.1 Application of thermal conductive paste by screen printing
It’s everything but easy to apply thermal conductive paste manually with a constant thickness in the ?m-range. Homogenity and reproducability of the resulting thermal layer are always questionable. Therefore it is recommended to apply the thermal conductive paste by screen printing (see figure 7). Besides applying the TCP homogeneously and reproducably, this method offers the possibility to adjust the distribution of the paste to the individual module.
Proposals for module specific drawings of such screen printing stencils can be requested using the normal Infineon channels. The suitability of the stencil in combination with the specific TCP and the assembly process and application has to be tested and qualified by the user.

6.2 Alternative: Applying TCP by roller or spatula
If the application of thermal conductive paste can’t be done by the recommended screen printing process, the paste could be applied using a roller or spatula alternatively. The layer thickness of the applied grease should be typically between 50μm and 100μm.
As a guideline for the required the amount of thermal conductive paste depending on the thickness d the following volumes can be given:
d = 50μm → VTCP≈0,4cm3
d = 100μm →VTCP ≈ 0,8cm3.
These volumes can be either measured with the aid of a syringe or applied from a tube.
Common rollers or fine toothed spatulas can be used to apply the thermal conductive paste. Unfortunately, the homogenity and reproducability of the resulting layer thickness is always questionable. For qualification and verification of the assembly process and during training phases, the thickness of the paste can be controlled by the aid of a wet film comb.



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