Wide Band-Gap Semiconductors

Wide band-gap semiconductors demand new thinking materials and interconnect techniques: –

Most interconnection at the packaging level with power devices uses aluminum wires in parallel arrays. This approach is satisfactory with Silicon because power density and thermal limitations constrain both die size and spacing. The area that is required for wire bonding is not a significant limiting factor.

WBG Substrates

SiC and GaN change all that and demand completely new thinking.- provide exciting opportuntites!

The dies themselves can be much smaller at a given power rating – down to 30% less – and the high temperature capability means that the dies can be placed much closer together. In addition, the long, thick wires used in power packaging present parasitic inductances. This is not an issue at the tens of KHz switching speeds of MOSFET and IGBT devices but at the 100KHz plus of SiC switching power supplies, parasitics become a real issue.

The high temperatures of SiC devices also accelerate the formation of Kirkendall voids in aluminum/gold combinations.

Al Wire LeadsWhiles ribbon is becoming more popular for power applications – there are a number of advantages including less heel cracking, reduced risk of pad cratering and greater current carrying cross-section- hear again the area required is large as with parallel wires.

The need for efficient thermal conductivity as well as high current suggests that the ‘MiB’ principle of aligning thermal and electrical paths should be applied for SiC packaging.

This could be achieved through 2.4D packaging techniques similar to those employed in very high volume device applications where additional silicon area is achieved by staking chips in ‘package on package’ configurations. In this case a mezzanine substrate could be used to provide both a planar interconnect from die electrodes to the outside world as well as a heat spreader/thermal pad.

The exciting capabilities of SiC semiconductors in high speed switching and power density, bring with them demands and opportunities for new packaging methods and materials, substantial modifications form the tried-and-true techniques in:-

  • Package substrate materials
  • Die attach/bonding
  • In-package interconnections
  • Moulding/encapsulation
  • 2nd level(board level) interconnect and materials

Opportunity awaits

For more information, contact Bill Burr or Nick Pearne.

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BPA Consulting Ltd

Tel: +44 (0)1306 875500
Skype: bpa-consulting

Company No.: 3709460

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