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Building RF Power Transistors Test fixtures

Views: 4746


CJ

#57256

Building RF Power Transistors Test fixtures | 12 November, 2008

I have to build test fixtures for RF Power transistors. These components generate alot of heat so the PCB is soldered to a baseplate. The problem I am having is that I am getting too much solder flowing thru the via's and flooding the topside of the PCB. I have tried to use less solder, but I know I need to have enough solder between the PCB and baseplate in order to get a coverage for ground. Does anyone have any suggestions on how I can solder the PCB to the baseplate?

Thanks

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#57261

Building RF Power Transistors Test fixtures | 12 November, 2008

How about plugging the via with a temporary solder mask or coving them with thermal tape?

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CJ

#57267

Building RF Power Transistors Test fixtures | 13 November, 2008

I have tried covering the vias with thermal tape and that did not work. I like the idea of plugging the via with a temporary solder mask. I will try that the next time I build a fixture which should be tomorrow. This is mainly a problem only because the PCB is gold plated and my boss does not like the way the fixture looks when the solder gets on topside of the PCB. IF the PCB had a silver color finish this would not be a problem because the solder would just blend in.

Thanks

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CJ

#57292

Building RF Power Transistors Test fixtures | 14 November, 2008

Plugging the holes with temporary solder mask helped some, but once the solder starts to reflow, the fumes from the flux pushed the solder mask out. What I ended up doing in addition to using the temporary solder mask was covering the areas of pcb with thermal tape that I definitely did not want solder on. This was time consuming, but it was worth it. After reflowing the fixture, I only had to wick the solder off of the areas around the vias.

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#57296

Building RF Power Transistors Test fixtures | 15 November, 2008

So next time that you order boards from your fabricator, consider asking the your fab to cap these pesky via on the solder side with SR1000 [or whatever they think will be good and cheap]. Think of the money you'll save. Your boss will be ecstatic!!! And you, you'll have time for a coffee and to chat-up that cute lil' so-and-so at the copy machine.

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CJ

#57300

Building RF Power Transistors Test fixtures | 16 November, 2008

Thanks for the tip on SR1000.

> Think of the money you'll save. Your boss will be > ecstatic!!! And you, you'll have time for a > coffee and to chat-up that cute lil' so-and-so at > the copy machine.

I like the way that you think! :)

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#57309

Building RF Power Transistors Test fixtures | 17 November, 2008

Continuing with the idea of capping the via with SR1000: If you have boards in-stock that will require all the putzing around that you've doing to prevent the solder flowing through the via, consider reworking your stock with SR1000 to prevent all the extra work. It's not hard to do.

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CJ

#57319

Building RF Power Transistors Test fixtures | 18 November, 2008

Fortunately, I only have one more set of boards left. I may or may not have to assembly, I have not gotten the word yet. Anyway, it would be good to know how to rework the boards with SR1000. I usually do not have any input when design team spins a board, and I get left with trying to solve a problem like this one after I get the boards.

Could you provide me information on how to do that rework?

Thanks

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#57345

Building RF Power Transistors Test fixtures | 19 November, 2008

Here you go: * http://www.engineeringlab.com/soldermask1.html

* http://www.circuitrework.com/guides/2-4-1.shtml

... or just go to Walgreens, buy some finger nail polish, and paint all the via with the polish.

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CJ

#57358

Building RF Power Transistors Test fixtures | 20 November, 2008

Thanks, I guess I was making this harder than what it is. I don't know why I did not checkout Circuit technology Center's website. I have been there before.

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CJ

#57568

Building RF Power Transistors Test fixtures | 10 December, 2008

Just to update. I tried using the temporary solder mask again and it worked great. I guess the first time I did not let the mask to cure long enough. Also, I inquired about have the via's plugged with SR1000 in the future and I was told by our PCB designer that the place that builds our boards charges to much for that.

Thanks again.

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#57571

Building RF Power Transistors Test fixtures | 10 December, 2008

So, this fine designer thinks the cost of you putzing around with is thing is cheaper to the comapny?

No. The fine designer is measured on in-bound cost, but not on the impact on overhead of those in-bound costs.

OK, try this one: Have your fabricator apply the removeable solder mask.

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