OTP versus soldering process

[felixc]

Hi,
I have the option to use OTP microcontrollers (an old 87C42) on a surface-mounted board. I am wondering if the OTP can lose its contents when it is subected to the heat of the surface mount reflow. Or should I use sockets all the time? Did anyone go through an issue like this?
Felixc

 

[MacGyverS2000]

Follow the datasheet's specified heat flow cycle and you'll be fine. I'm surprised to find an OTP in surface mount config, though... didn't realize they still made those combinations.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[leonar40]

You should be fine but I would highly recommend using a flash microcontroller like most of the Microchip PIC families. You can get them in surface mount packages and include a connector on your board for reprogramming them right in the circuit (without having to take the chip off the board).

 

[felixc]

Surface mounted OTPs were a popular item 10 years ago, before flash started taking the place. Unfortunately Intel does not support these products anymore, although they still make them.

leonar40, this is for a "shrink down" design, that allows no software rewriting, so I am stuck with this MCU. Take a look at the Zilog Z8Encore chips, they're cheaper than the equivalent PICs.

 

[IRstuff]

OTP's used to come in two varieties, fuse-link and EPROM. The fuse-link variety were programmed by physical destruction of fuses, which was extremely permanent and not affected by temperature.

The EPROM variety was basically a UV-erasable EPROM without a window, hence OTP. Slightly less robust, but a short jaunt through a reflow machine should be no big deal, since they were capable of maintaining storage at 125ºC junction temperatures for years.

TTFN

 

[nbucska]

isn't OTP cheaper than FLASH ?


<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[felixc]

It is an older technology. Flash devices are now cheaper to produce.
I'll try to manage enough space for PLCC SMT sockets so both ways will do.

 

[WorkedVYSV8]

The answer to your questions is no, unless you are applying MASSIVE amounts of heat, this is in the data sheet.

Flash devices are only now starting to be cheaper for 8 bit processors, i can still get fairly powerful 8bit OTP processors from motorola that do the job and are dirt cheap...

I actually just started a design with a 16K ROM, 1.1K ram, full LCD driver, DTMF encoder/decoder, 4 8 bit i/o ports, PLL, timers, interputs etc for US$1.60... Like to see somthing like that in flash not likely but would LOVE to be proven wrong!! (i only really need the DTMF enconder/decoder, but this is cheaper than mode DTMF encoder/decoders that i could find with a cheap micro)