This is somewhat weird...
I have a TMP006 wired up on a double-sided FR4 PCB. This board was manufactured in-house as a quick-turn prototype, has 1oz copper on a 1.6mm laminate, and no solder mask. This is the same board for which I requested design advice in a previous thread. There IS a metal pad under the centre of the chip (grounded), but it doesn't have an insulating solder mask over it. The IC was soldered with paste flux (which has been removed with an ultrasonic cleaner and electronics-grade Isopropyl Alcohol) and a hot-air soldering station (preheater and hot-air jet).
The Gerber files for the board are in my 'files' area.
The TMP006's Ambient sensor seems to be behaving itself, and is reading 25C in my fairly warm office / lab (that'll teach me to leave the heating on). Thing is, the IR sensor is misbehaving quite badly. If I leave the sensor in 'free air' (actually mounted in a Panavise), I get these values in the registers:
R[0] (Vobject) = 0xFBE1
R[1] (Tambient) = 0x0C5C
Putting this into the TMP006 spreadsheet results in an ambient temperature of 24.718750 Celsius... and an object temperature of 2.295038 Celsius...
OK, so what happens if I put my hand about an inch above the sensor?
R[0] (Vobject) = 0xFA82
R[1] (Tambient) = 0x0C6C
Putting this into the spreadsheet gets me an ambient temperature of 24.843750 Celsius... and an object temperature of -8.337225 Celsius. Now, I've been accused of having cold hands, but if they were that cold I doubt I'd be typing this message!
So, here's the question -- what's going on? Is it possible that the exposed copper pad is shorting out the IR sensor? Would I be better off removing it if I can't place an insulating solder mask over it?
Thanks,
Phil.