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AN-9190
Impact of DBC Oxidation on(A)SPM Module Performancewww.onsemi.com
Introduction

APPLICATION NOTE(A)SPM modules with Direct Bonded Copper (DBC),
substrates aim for high thermal performance. The backsideof the DBC substrate is formed by a bare copper layer which
is supposed to contact external heat sink through thermal
grease or any other Thermal Interface Material (TIM). The
surface of the copper layer may get oxidized when it is
exposed to the atmosphere during storage or themanufacturing process. The objective of this AN−9190 is toclear up the concerns on any performance degradation dueto the DBC oxidation by illustrating the effect of copperoxide layer on the thermal and electrical characteristics of(A)SPM products and proving that there is no impact on theperformance of the modules.

What is Copper Oxidation?

The copper oxide consists normally of Cu2O or CuO. The
oxide layer is formed very thin and non−uniformly. For
example, the thickness of oxide is known to reach around
125 nm when the copper surface is exposed to air at 200°C
for 1 hour.[2] Actual measurements performed with special
equipments show that thickness of oxidation layers oftypical oxidized samples are from 1.8 nm to 14 nm.

What is DBC?

As seen from Figure 1, the DBC substrate is composed ofa thin ceramic layer with a sheet of copper bonded to bothsides by a high−temperature oxidation process. It is
commonly used in power modules because of its excellent
thermal conductivity. The top copper layer can bechemically etched using printed circuit board technology toform an electrical circuit, while the bottom copper layer isusually kept plain.

Figure 2. DBC Oxidation Process

Oxidation starts with the formation of Cu2O, which is redor pink in color, when copper atoms initially react withoxygen molecules in the air. [3]2Cu ) O 2 ³ Cu 2O(eq. 1)

Cu2O can be further oxidized to CuO which is black incolor.
2Cu 2O ) O 2 ³ 4CuO

(eq. 2)In the case of SPM products, a very thin Cu2O layer canbe generated if exposed to air for a long time. It is known thatthe storage in a high temperature and high humidity setting
would accelerate Cu oxidization. It is better to keep thedevices in an environment with humidity of50 +25/−20% RH and temperature of 24 ± 5°C.
Figure 1. Structure of DBC

Thermal Performance

Thermal characteristics of semiconductor packages arerepresented as thermal resistance, Rthjc and Rthjs. The
thermal resistance by conduction is expressed as following:

Alumina (Al2O3) or Aluminum nitride (AlN) are used as
ceramic material. AlN has much better thermal conductivity(> 150 W/mK) than Al2O3 (24−28 W/mK) but is much more
expensive. The DBC substrates have excellent electricalinsulation and good heat spreading characteristics.[1]© Semiconductor Components Industries, LLC, 2019

September, 2019 − Rev. 3

R th,conduction + LkA(eq. 3)

whereRth, conduction is thermal resistance of solid conductor in[℃/W]
1Publication Order Number:
AN−9190/D

AN−9190
L is thickness of solid conductor in [m]A is heat dissipation area of solid conductor in [m2]k is thermal conductivity of solid conductor in [W/m°C]

Table 2. DETAILS OF Rthjs

Rthjc is thermal resistance from junction−to−case andrelated to the package structure. Rthjs is thermal resistancefrom junction−to−sink and includes the thermal resistanceof the contact between package and external heat sink.
Figure 3 shows a general cross sectional view of an(A)SPM package mounted on a heat sink. Thermal grease
with a thermal conductivity of 1 W/mK is commonly usedin order to reduce the thermal resistance of the contact. The
thickness of thermal grease is assumed to be around 50 mm
in (A)SPM package.
Rthjc and Rthjs of the (A)SPM package is expressed as thesum of thermal resistances of each layer as shown in Table
1 and Table 2 respectively. These results are generated byFloTherm, thermal analysis software based on thedimensions and properties of the each material. The thermal
resistance of copper oxide layer is 0.0021% of the Rthjc, and0.0013% of the Rthjs when the thickness of copper oxide is
100 nm and thermal conductivity is 10 W/m°C.
Contribution of copper oxide layer to Rthjc and Rthjs is sosmall that the copper oxide layer does not affect the thermal
performance of (A)SPM package.

Rth_Top Cu

1.50%

Rth_Al2O3 Substrate

47.85%

Rth_Bottom Cu

0.54%

Rth_OxideLayer

0.0013%

Rth_thermal Grease

40.67%

Rthjs

100.00%

Rth_chip

5.80%

Rth_adhesive

3.65%

Actual measurements of thermal resistance were also
performed with the FSBB30CH60 and FSBB20CH60 toprove the software analysis. Measured Rthjc with oxidized
samples and non−oxidized samples showed similar values
and the difference is smaller than measurement tolerance
5%. According to the test result and simulation outcome, it
can be concluded that Oxidation of DBC does not have any
impact on thermal resistance.
Isolation Voltage

DBC oxidation does not have any impact on electricalcharacteristics of (A)SPM products because all electricalcomponents such as IGBT’s, diodes, IC’s, bootstrap diodes,
lead−frame, and bonding wires are totally isolated from theexternal copper layer of the DBC.
There is no degradation of isolation voltage. It is theceramic layer in the middle of the DBC that provides thehigh level of isolation. Therefore, the oxidized copper layer
does not have any impact on the isolation voltage level of(A)SPM products.
Examples of Oxidized DBC

As seen from Figure 4, fresh copper layer is a golden color
for SPM3 and ASPM27 series modules.

Figure 3. Cross Section View of SPM Package
Table 1. DETAILS OF Rthjc
Rthjc

100.00%

Rth_chip

9.78%

Rth_adhesive

6.15%

Rth_Top Cu

2.52%

Rth_Al2O3 Substrate

80.64%

Rth_Bottom Cu

0.91%

Rth_OxideLayer

0.0021%Figure 4. Fresh Sample

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AN−9190
Figure 5 shows oxidized copper layer as time passed fromcopper atoms reacted with oxygen molecules in the air.

Figure 8 is a sample for a fingerprint or glove mark whenusers are assembling or touching the modules directly on theproduction line. It can cause oxidation on the copper layerby sweat. However, there are no effects with the modules

Figure 5. Oxidized Sample

Figure 6 shows an example of oxidized copper layer withpicker circle printing of SPM3 and ASPM 27 series
modules.

Figure 8. Fingerprint Mark

Figure 9 shows discolor and oxidation by water remainedon DBC surface. Water remain and splash in manufacturing
process by high humidity, old equipment or facilities etc.

Figure 6. Pick−up Nozzle MarkThe picker circle printing is just trace of handler in mass
product line. Please refer to the Figure 7.

Figure 9. Water MarkConclusion

The exposed DBC copper layer of the SPM package canbe oxidized during storage or the manufacturing process.
The oxide layer formed is very thin on the outer surface. But
the impact of the oxidation on thermal resistance isnegligible, and there is no degradation of isolation voltageof the package. The oxidized copper layer does not affectthermal performance, electrical characteristics and productreliability.

Figure 7. Picker Picture

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AN−9190
References

FSBB30CH60D – Product Folder
FSBB10CH120D – Product FolderFSBB10CH120DF – Product Folder
FNA23512A – Product Folder
FNA22512A – Product Folder
FNA21012A – Product Folder
AN−9086 — SPM 3 Package Mounting Guidance
RD−404 — Reference Design of FSBB10CH120D
RD−354 — Reference Design of 1200V Motion SPM 2Series
AN−9075 − Users Guide for 1200V SPM 2 Series
AN−9076 − Mounting Guide for New SPM 2 Package
AN−9079 − Thermal Performance of 1200V Motion SPM 2Series by Mounting Torque[1] http://en.wikipedia.org/wiki/Power_electronic_subst
rate[2] S. Cho, K. Paik, and Y. Kim, “The effect of theoxidation of Cu−Base Lead Frame on the Interface
Adhesion between Cu Metal and Epoxy MoldingCompound”, IEEE Transactions on Components,
Packaging, and Manufacturing Technology−Part B,
Vol20,No2, May1997, pp167~175.
[3] http://en.wikipedia.org/wiki/Copper%28I%29_oxide
Related Resources

NFVA33065L32 − Product Folder
NFVA34065L32 − Product Folder
NFVA35065L32 − Product Folder
FSBB30CH60C – Product Folder

SPM is a registered trademark of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries.
ON Semiconductor andare trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries.
ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor’s product/patent
coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein.
ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards,
regardless of any support or applications information provided by ON Semiconductor. “Typical” parameters which may be provided in ON Semiconductor data sheets and/orspecifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer
application by customer’s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are notdesigned, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification
in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized
application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, andexpenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if suchclaim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This
literature is subject to all applicable copyright laws and is not for resale in any manner.

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AN−9190/D