Re: UBITX V3 TX GAIN VARIATIONS

Jerry Gaffke
 

Parts do not come with solder on the pins.

When manufacturing, the usual process is to lay a stainless steel mask over the board with holes cut into it for each pad,
then squeegie on some solder-paste, which is solder with the consistency of play-dough.
Then auto-insert all those dinky R's and C's and transistors with a pick-and-place machine.
Send the board through a heat process of some sort.
Surface tension of the melted solder tends to pull any slightly wayward arts into the center of their pads.

Some hobbyists do this by applying solderpaste from a syringe, laying down a straight bead across consecutive pads
on something like a QFP with 100 pins on 20 mil centers. Then run it through a toaster oven.
When the solder melts it will adhere to the pad and separate nicely to one little blob per pin/pad.
    http://store.curiousinventor.com/guides/Surface_Mount_Soldering/Solder_Paste_and_Toaster_Oven

For rework on a uBitx of course, you can't use a toaster oven.
I'd melt some ChipQuik low temp solder alloy in around the part to be removed using a soldering pencil,
then use something like an embossing gun (a hot air heat gun, maybe 250 watts?) to get the part 
hot enough to pluck it off the board with tweezers.  For R's and C's, it's easiest to take two soldering
pencils, one on each end simultaneously.  For 3 pin parts such as all those mmbt2n3904's, perhaps heat
up that single pin on one side with the soldeirng pencil and lift it up off the board using a knife, then 
free up the other two pins using two soldering pencils as if it was an R or C.

Jerry, KE7ER


On Fri, Aug 31, 2018 at 12:20 PM, Bo Barry wrote:
Question. Do the tiny parts have solder on them? I read about some that do and they can be mounted by using hair dryer. I assume you have to hold them down good.

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