Last April I wrote about the cheap Chinese SOIC-8 test clips. In that post I primarily discussed the wiring – specifically that, as wired, it isn’t useful for in-circuit programming of the ATTiny85 SMD SOIC-8W chip. Ultimately, I rewired the clip so that it would work correctly for the ATTiny85 SMD SOIC-8W chip. I went on to use the chip quite successfully, programming a number of ATTiny85 SMD SOIC-8W chips while in-circuit. I was thinking that this cheap Chinese test clip was pretty good until today. I had extreme difficulty getting it to program in-circuit on one board and this was right after a good program on another board. Since one board programmed successfully I assumed that the second board had a problem and, after a lot of investigative work ended up tearing the board apart piece by piece when the problem was actually in the test clip.
With further, magnified, investigation (see photos below) I discovered that (1) the clip rode too high on the chip; (2) slight variation in chip profile made some chips fail when others would work; (3) the culprit was the clip’s retention spurs – little extensions of the plastic part of the clip that are intended to grasp the IC around its base and hold the clip firmly in place with good contact to pin connection. The plastic is simply too soft for the retention spurs to survive very long – I probably used it less than a dozen times before it failed.
I thought that a better brand of test clip might not have this problem but, after reading THIS ARTICLE and also THIS ARTICLE, it seems that it is a universal problem and that the brand-name clips are no better. I am going to be forced to abandon in-circuit programming using a SOIC-8 test clip and, instead, I’ll design in a programming connector. A 10 or even 6 pin ISP connector is too large for my boards so I may just put in some plated-through holes for pogo pin connection and create a custom programmer cable with the pogo pins secured in a small PCB. TAG-CONNECT cables and pads are one solution but I think that I’ll probably just roll my own.
UPDATE: On eBay I found and interesting pogo pin adapter for SOIC-8 chips. Unfortunately, its pins are at 5.08mm which is designed for a standard SOIC-8 (SOIC-8-N) and the ATTiny84 SMD package uses a SOIC-8-W (wide) package and this adapter’s pins will not clear the case – so, no good for the ATTiny85. I’ve been wondering if I can 3D print my own pogo-pin adapter? Hmmm – I’ll ponder on that while I wait for my new 3D Build-One printer to arrive. I’ve retired my old OneUp printer as it was getting too loose for good prints.
For new designs TINDIE has a pretty neat little Tiny AVR-ISP pogo-pin programming adapter.