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  • Author Author: Jan Cumps
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Hercules LaunchPad and GaN FETs - Side Note B: Look at the PCB

Jan Cumps

I'm designing a BoosterPack to evaluate GaN devices with the help of a microcontroller.

I've received PCBs from Seeed. Let's have a look ...

image

 

This is my first Seeed order (a kind element14 community member gave me a rebate coupon that I happily used).

Board specifications:

 

  • PCB Dimension - 10cm Max*10cm Max
  • Layer - 4
  • PCB Thickness - 1.6mm
  • PCB Qty. - 5
  • PCB Color - Green
  • Surface Finish - ENIG
  • Copper Weight - 1oz.
  • Panelized PCBs - 1
  • Expedited Option - NO

 

The price without shipment for this board is 65.12€. Shipping was 7.37€. The coupon got me 9.15€ off ($ 10). Totals to 63.97€

image

This design requires 2oZ copper layers. My budget can't carry the cost of such a board - so I will not be able to draw full current out of my design.

This is a compromise, one of the many I had to make. I tried to avoid compromises in the design, but did make them when ordering.

Getting a board that has enough copper on it will not require a design change. It's just ticking a different option when ordering and coughing up the monies.

I'd rather do that after I validated that I didn't make mistakes in the PCB layout.

image

image

Just like previous designs I did with OSHPark, the Seeed boards look very good at first inspection.

This design is 4 layers, so I have no mechanism to look at the two inner layers. The top and bottom layer look very nice, so that's a good sign.

 

In the images below, the artist renditions on the left side are generated by the Seeed portal.

The photos on the right side are the actual thing. Click on them to get a detailed view.

 

imageimage
imageimage

 

 

Populate Order

This is the first time I'll populate a two-sided board. I'll use hot air for the smd components.This is how I plan to approach it:

  1. solder the GaN IC and the inductor. These two have the pins under the device. I'll have to massively bombard them with heat to transfer the energy underneath where the solder paste is.
    I'll use the pre-heater that shabaz gave  me to get the whole board to a close-to-reflow temperature.
  2. then all the smd components on the bottom side. If they fll of later, that's not a big deal, because the are only few.
    I'll also use the pre-heater but on lower temperature, because its heat will be radiating on the inductor and GaN chip.
  3. Then I'll do the remaining top smd components.
    The pre-heater again on a temperature low enough to not desolder the bottom components.
  4. the trough-hole components by hand

 

It is my first time. I'd be happy to take your advice on the preferred order to solder the components.

The tools I have at hand:

  • hot air
  • soldering iron
  • pre-heater

 

 

edit: I've attached the waveform of one High input pulse as hi01.wfm.

If you have a Rigol DS1052E you can upload that to your scope and examine the ringing with cursors.

image

 

 

Related Blogs
Hercules LaunchPad and GaN FETs - Part 1: Control Big Power with a Flimsy Mouse Scroll Wheel
Hercules LaunchPad and GaN FETs - Part 2: Make a BoosterPack
Hercules LaunchPad and GaN FETs - Part 3a: BoosterPack Layout - Reference Design
Hercules LaunchPad and GaN FETs - Part 3b: BoosterPack Layout - my version
Hercules LaunchPad and GaN FETs - Side Note A: BoosterPack Layout - Custom KiCad Parts
Hercules LaunchPad and GaN FETs - Side Note B: Look at the PCB
Rotary Encoders - Part 1: Electronics
Checking Out GaN Half-Bridge Power Stage: Texas Instruments LMG5200 - Part 1: Preview
Rotary Encoders - Part 4: Capturing Input on a Texas Instruments Hercules LaunchPad with eQEP
Vintage Turntable repair: Can I fix a Perpetuum Ebner from 1958 - part 4 - Hercules LaunchPad Enhanced PWM try-out
Attachments:
hi01.zip
  • in reply to Jan Cumps

    When you have the footprint of the terminal blocks wrong and you don't want to drill new holes trough a 4-layer board:

     

    image

  • in reply to Jan Cumps

    I've fixed the board layout for C30, P2 and P3. New archives are attached to the relevant posts.

    C30 was me selecting a wrong existing footprint.

     

    P2 and P3 is pure blindness and lack of feeling for numbers.

    In the KiCAD footprint editor, I had put the (0.0) in the middle of the connector.

    I should have then placed pin 1 on X coordinate -(distance between pins)/2. Pin 2 on X coordinate +(distance between pins)/2.

    Silly me first halved the distance, and then applied above formulas.

    Doh.

  • in reply to Jan Cumps

    The levels work nicely with the 3.3V signal from the processor board without having to do any level conversion.

     

    Looks like you're going to be ok with the signals.

  • Captures annotated with the hysteresis info.

     

    The orange cursor (B) for the rising edge

    The white cursor (A) for the falling edge

     

     

    image

     

    Typical IC:

    image

     

    Lowest in bell curve:

    image

    Highest in bell curve:

     

    image

     

    Extreme Low and High (this is hypothetical. hysteresis is always 400 mV):

    image

     

    And the frequency of the ringing. 100 MHz as indicated by Jon.

    image

  • in reply to jc2048

    Jon Clift wrote:

     

    So it's working. What do you think the problem was before?

    I had soldered the first GaN device two times. I think it had too much heat.

     

    What happened:

    I put the GaN IC and the inductor as first on the board, because they are the only ones with pads under the device.

    The GaN chip reflowed nicely and the capillary effect pulled it right on the pads.

    But the inductor has a strange tendency to twist on its footprint. And it is so close to the GaN chip that it pushed it off the pads.

    (you can see in both Michael's and my photo that for both of us the inductor isn't square in its footprint:)

    image

     

    So I had to first heat up the GaN chip again to remove it from the board (I had to heat it for significant time before it decided to give).

    Then, after cleaning the pads and re-applying paste, I had to reflow it again, 3rd time it had a blast of hot air over it.

    Internally, this hybrid GaN device has a pcb inside its package, so that may have reflowed along the way, during the unsoldering activity.

     

    I have removed it again, wicked the pads, applied fresh paste and soldered the new one in place.