Stablcore - CTE replacement for Thermount


STABLCORE® - CTE replacement solution for THERMOUNT®

Elmatica can deliver PCBs with STABLCORE 
from Europe and USA

STABLCOR® is an excellent replacement material for Thermount, when used in conjunction with FR4 and Polyimide.
If a designer has a multi layer board made from Thermount, he can directly replace that board now with multiple layers of
standard FR4, and 2-3 layers of STABLCOR® embedded in the PCB to achieve the desired Coefficient of Thermal Expansion (CTE)
to match their old design.
STABLCOR® even has the ability to tailor the CTE anywhere from 2.5ppm/°C to 12ppm/°C depending on the placement and
amount of the STABLCOR® material in the FR4/Polyimide stack-up.
See .pdf


Typical material application usage:

-  Thermount Replacement
-  Copper Invar Copper Replacement
-  Heavy Copper Replacement
-  Aluminum Heat Spreader Replacement
-  Thermal Interface Materials
-  Rigidity
-  Controlled CTE


Additional benefits:

-   Less than 50% Z-axis expansion of Thermount
-   No moisture absorption issue
-   PCB acts as Heat Spreader. Substantial increase in Thermal Conductivity
-   Increased Rigidity without increasing weight
-   Benefits in lowering lead-free assembly temperatures


STABLCORE test report (NASA)

see .PDF

Design guide lines for STABLCORE
see .PDF

Rigidity Design guide lines for STABLCORE
see .PDF


Data Sheets for Epoxy and Polyimide STABLCORE

ST10-EP387(Epoxy) Data Sheet
see .PDF

ST10-LC909(Polyimide) Data Sheet
see .PDF

ST325-EP387(Epoxy) Data Sheet
see .PDF


A technical description of CTE

CTE stands for Coefficient of Thermal Expansion. It describes a number of percentage relating to how much a PCB expands
as it is heated or cooled. Every material in the world expands or contracts with a change in temperature;
for example, your house doors are actually a little larger in the summer than in the winter.

Very few materials change for the negative like carbon fiber, so the part shrinks when it experiences a rise in temperature.
But most items expand by a small percentage as they heat up. The expansion is expressed in parts per million
per degree Celsius (ppm/°C).

A PCB will expand in length or width by 14 parts per million per Celsius degree.  This means that if a PCB were 1 million inches long,
it would expand by 14 inches for every Celsius degree of temperature increase.

A typical FR-4 laminate used in PCB’s have a CTE of 14 to 17 ppm/°C. This is fine; until we consider that the large silicon chip packages
like FPGA’s we solder onto a PCB have an expansion rate as low as 6 ppm/°C.

The difference in expansion rate is enough, (especially on the larger BGA packages), that when the PCB and chip are heated up, the PCB will expand
more than the FPGA chip package and shear the solder joins off the chip.

So, how does CTE affect the board and the way we design and fabricate them?
When selecting the laminate in an attempt to reduce CTE, we notice many of the FR-4 brands have similar CTE values, and most
are far too high (14 ppm/°C) to be used with large sili-con packaging.
This is where using carbon fiber or STABLCOR inside your PCB can lower the surface expan-sion to more closely match that of your chip.

The alternative is to use metal cores like CIC and CMC, which feature CTEs of 8 ppm/°C and 6 ppm/°C, respectively. The metal core is used to anchor the expansion of the FR-4 outer layers and provide an overall CTE of 12 ppm/°C and 9 ppm/°C, respectively.

However both these solutions are very expensive and have problems with fine features drill-ing through thick metal.

As low-CTE laminates go, the most expensive are metal cores, followed by Kevlar and Aramid fiber laminates. All of the low-CTE cores
are hard to drill and process, except STABLCOR.                                             

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