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HMC8500 Bias Problem and Soldering


We have made a small PA board using HMC8500PM5E, I have few problems.

1- While soldering using hot air gun, top of the IC just melted. Soldering maximum temperature says 260 degrees, but it is just same for other ICs which we dont have any problems at all, I am attaching a picture just to show it. When we soldered from bottom it was fine. We are guessing that, top of the IC is a different material which is a soft one to conduct the temperature, is that right?

2- For Biasing, I follow similar steps to datasheet. I apply -4V to Vgg/RFIN pin, then apply +28V to Vdd/RFout pin, then turn on the RFIN signal. I dont see anything working, when I check the Igg there is no current at all. Design is very similar to the EVAL board. When I remove R1(25ohm, page 14 on datasheet) to check the current, I see no current, and smokes start coming from the PA. What could be the issue?

3- Also, is it normal that when everything is powered off, the resistance between the Vdd/RFout pin and ground is 0.6 ohm?

Best regards.

photo added
[edited by: baykalyu at 12:14 PM (GMT -5) on 29 Dec 2021]
  • I found the solution.

    So obviously the datasheet is correct, I had no idea that the Vgg would be so important, but when I removed my regulator and applied Vgg externally. Vgg at -2V made the PA work, it does absolutely nothing when it is at -3V, but suddenly starts working below -2.5V. I will modify the LDO output and use it as it is.

    The melted IC works just fine, so it is not damaged. As I said it is probably some heat transfer material.

  • Hi Bayklyu,

                       The package used in the manufacture of the HMC8500 is not a solid injection molded package. It is a pre-molded package with a lid epoxied on top, (air cavity). That is why you experienced melting.


    Jim B