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DQN, X2SON, DPW packages disambiguation, and land/stencil problems

lloyd konneker
Expert 1790 points
Other Parts Discussed in Thread: TPS3839

For TPS3839, the package is "DQN (S-PX2SON-N4)."  While for other parts there is a DPW package also loosely called X2SON, but having different lead pitches and land dimensions.  Can you help me understand the nomenclature, which are industry standard and do they just describe the relative positions without prescribing a pitch?

The DQN land pattern has only 0.1mm (4mil) between pins and the thermal land.  That is less than the typical minimum between pins (8mil) of many PCB fabricators.  Worse, the distance between paste is only about 0.15mm, which makes for a very thin web on the stencil.

The DQN land pattern has a thermal pad that is larger (0.58) than the thermal pin under the chip (0.48).  If the pin on the chip sticks out from 0.0 to 0.05 mm, I suppose the intent is to get a fillet underneath the chip?

Is soldering the thermal pad really necessary on the TPS3839 which only uses 150nA?  Do you really need the mechanical strength since the part is so small, any board bending should not stress the part?

Also, TI doc SLUA271 suggests that a land pattern for a pin extend 0.4mm past the component outline and pin.  The DQN only extends 0.2mm.  I suppose the DQN is not a member of the QFN family, since the pins have trapezoidal shape?

The context is, I am a hobbyist and have suffered 2 failures in 7 boards.  I am wondering if there is not an alternate land pattern and stencil pattern for this part.

  • 0
    TI__Expert 3540 points

    Can you help me understand the nomenclature, which are industry standard and do they just describe the relative positions without prescribing a pitch?
    For example, for "DQN (S-PX2SON-N4)"

    "DQN" is the TI Package Name also known as in datasheets as Package Drawing (Reference Code)
    "X2SON" is the Package Type, which is the same across the industry
    "4" is the number of pins (not taking in account the Thermal Pad)

    I'd recommend you visit TI's Packaging Information site for more packaging information

    Is soldering the thermal pad really necessary on the TPS3839 which only uses 150nA?  Do you really need the mechanical strength since the part is so small, any board bending should not stress the part?

    It is recommended (as seen on the Datasheet), that the Thermal Pad is "connected to ground or to a floating copper plane for mechanical stability"

    Also, TI doc SLUA271 suggests that a land pattern for a pin extend 0.4mm past the component outline and pin.  The DQN only extends 0.2mm.  I suppose the DQN is not a member of the QFN family, since the pins have trapezoidal shape?

    SLUA271 mentions "TI uses a typical value of 0.4 mm toe length beyond the package body as a standard...", however, it also mentiones "It is recommended that the PCB lead finger pad be designed a minimum of 0.1 mm longer than the package land length...".

    For the TPS3839 in the X2SON package the recommendation is 0.2 mm.

    Also, DQN is not part of the "Quad Flat No Lead (QFN)" package type, but rather part of "Small Outline No Lead (SON)" (as its package type is X2SON), you can see this here: http://www.ti.com/packaging/docs/searchtipackages.tsp?packageName=SON.

    When in doubt you can look up a part by TI Package number (e.g. www.ti.com/.../searchproductbypackage.tsp)

  • 0 in reply to Victor Salomon
    Expert 1790 points
    Thanks, that is very informative.

    In my case, I think the essential point is "or a floating copper plane for mechanical stability", which is kinda hidden in the TPS3839 data sheet, and more specialized than the DQN document (which says it is for thermal purposes.) I'm not designing a cell phone, mechanical stress is not a concern.

    It turns out only one of my two failures is attributable to the TPS3839, where the part is skewed on the board, maybe my hand placement was off and I suppose one pin was sucked to the thermal land. But my stencil leaves a horrible glob of paste over the whole part (again, hobbyist, I don't clean the stencil after every squeeze.) So I'm planning on eliminating the thermal pad.

    Finally, using KiCad software, it is a pain to design a trapezoidal pad (you must overlap many regular shaped pads having the same pin number) And with OSHPark PCB fabricator the PCB comes out with ragged pads (I'm guessing it is a rounding error somewhere.) So I'm pondering just using rounded rectangular pads.