QFN / DFN / MLF

Challenges and of Solutions for Contacting Quad Flat No-Lead / Dual Flat No-Lead / Micro Lead Frame

  • Features

    • wide variety of pitches, sizes, and pin counts
    • used for a wide range of applications
    • low cost packages
    • typically NiPd or tin plated
    • most have exposed ground pad
    • very high volume
  • Contacting Challenges

    • high currents
    • high voltages
    • recessed pads
    • device asymmetry
    • Kelvin test
    • tin migration
    • high contact spring wear on NiPd platings
    • tin oxide on leads
  • Contactor Features for QFN, DFN & MLF Packages

    • self-cleaning wipe
    • wide spring tips
    • high contact force
    • relatively high surface area for heat dissipation
    • relatively high thermal mass
    • durable one piece design
    • low and stable contact resistance
    • high current carrying capability
    • large mechanical operating window for stable contactor performance

DFN / QFN / MLF Packages

DFN / QFN / MLFs are leadframe or organic substrate based packages that are usually encapsuled in a rectangular plastic body with contact pads on two or four sides. For better thermal performance, most DFN /QFN / MLFs have exposed pads, typically on the bottom of the device. DFN /QFN / MLFs are industry standard sized and the pads are typically spaced at pitches ranging from 0.35 mm to 0.65 mm.

Challenges

DFN / QFN / MLFs can be tested as single devices or in Strip form. In both cases ensuring a stable contact even if there is tin oxide on the device leads is critical. With multiple retests at different temperatures the contact pressure and wipe need to be aggressive enough to penetrate the tin oxide layer without resulting in exposed cooper. Also, since DFN / QFN / MLFs are an industry standard packaging that is suited for many different applications, the test requirements can vary a lot.

For singulated devices, due to the trim and form process, the geometry of the leads is not always symmetric contactable part of the device lead. Since the contactable portion of the device lead is usually at an angle, it causes a lateral force at the point of contact.

For strip applications in cases where DFN / QFN / MLFs are tested with extremely high currents, a contacting technology that can handle these high current without sacrificing the capability of testing at high parallelism is required.

Addressing the Challenges

Since there is a wide variety of tin alloys and NiPd based lead platings, Xcerra offers a wide variety of Kelvin and non-Kelvin cantilever springs with different tip styles, geometries and platings, designed to address the issues of tin oxidation and wear out. Xcerra cantilever springs have a high compliance window to compensate for coplanarity issues of the DFN / QFN / MLF leads.

The durable one piece design of Xcerra’s BlueLine and Link contactors allows for lateral forces at the point of contact, without damaging the contact spring tip.

Each socket is manufactured out of high quality materials and custom designed of match the customers test requirements.