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Step 11Building - The surface mount
When soldering a PCB you normally start with the smallest devices first so I started with the FT232R USB-to-Serial chip that is a SOIC28-device with the pins as 0.65 mm interval. Thats really tight. But it's not impossible to solder it even with a rather wide tip on your soldering iron.
I started by putting a layer of solder on the pads where the chip would be mounted. I had to use a desoldering wick to remove excess solder from a few of the pads where solderbridges between the pads were.
Then I put the chip on to the pads and carefully adjusted the position of it. I then touched one of the corner pins of the chip with the tip of the soldering iron so that the solder below it melted. I checked that the rest of the pins still were on the pads and had not been skewed and did the same thing with the pin at the opposite corner.
Now the chip were securely fastened I held the tip on each pin (or more likely, two pins at the same time) for a second or two so that all pins got soldered onto the pads.
I checked for unwanted bridges between the pins with a bright light an a magnifying glass and it all looked good straight away.
So I temporary installed the capacitor that handles the 3.3 volt generation for the chip and the USB-connector and plugged it in to the computer.
The computer said Bing-Bong! A new USB device and a new Serial port was detected. So far so good.
As you can see in the picture I had to put a piece of insulating tape due to a minor mistake in the layout of the circuit. I forgot that the USB connector is metallic on its underside and that will short circuit any connections or vias that is beneath it - and I had three vias there. Oh well, the next generation of boards will be better.
I started by putting a layer of solder on the pads where the chip would be mounted. I had to use a desoldering wick to remove excess solder from a few of the pads where solderbridges between the pads were.
Then I put the chip on to the pads and carefully adjusted the position of it. I then touched one of the corner pins of the chip with the tip of the soldering iron so that the solder below it melted. I checked that the rest of the pins still were on the pads and had not been skewed and did the same thing with the pin at the opposite corner.
Now the chip were securely fastened I held the tip on each pin (or more likely, two pins at the same time) for a second or two so that all pins got soldered onto the pads.
I checked for unwanted bridges between the pins with a bright light an a magnifying glass and it all looked good straight away.
So I temporary installed the capacitor that handles the 3.3 volt generation for the chip and the USB-connector and plugged it in to the computer.
The computer said Bing-Bong! A new USB device and a new Serial port was detected. So far so good.
As you can see in the picture I had to put a piece of insulating tape due to a minor mistake in the layout of the circuit. I forgot that the USB connector is metallic on its underside and that will short circuit any connections or vias that is beneath it - and I had three vias there. Oh well, the next generation of boards will be better.
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