Pre-Program SMD PIC Before Soldering?

[Angry Badger]

Hi,

Just about to solder my first smd PIC onto a pcb. Wondering whether it should be pre-programmed before soldering it to the board. That way when power first applied to cct (via ICSP) either it or other chips connected to it won't be damaged due to possibly incorrect states on i/o pins.

Necessary or not?

Thanks in advance for any advice.

 

[Nigel Goodwin]

Not required, PIC's power up with all pins set as inputs.

But you shouldn't be designing your boards so damage could be caused anyway.

 

[colin55]

You have to make sure that the programming lines (pins) are not heavily loaded.
One or two LEDs in series on an output is ok as the line will go HIGH before drawing current when programming and the programmer will produce a HIGH.
But a resistive load of 25mA will be a problem with some programmers.
And a capacitive load between two programming line will create a problem.
I prefer to pre-program the PIC chip, then place it HARD on the board and turn the project on and see it work.
Then, when you solder the pins and it does not work, you have damaged the chip. I have not yet damaged a chip, but I do use a temp controlled iron and keep the temp below 320 degrees C
Some people prefer to use a higher temp and create a faster joint. There are merits to both methods.

 

[Nigel Goodwin]

Then, when you solder the pins and it does not work, you have damaged the chip. I have not yet damaged a chip, but I do use a temp controlled iron and keep the temp below 320 degrees C
Some people prefer to use a higher temp and create a faster joint. There are merits to both methods.

To be honest, damaging chips during soldering is EXTREMELY rare - and you would need to be exceptionally bad at soldering to do so.