Jan-Erik Soderholm wrote:

>Hi.
>I've been thinking of the issue of ICSP of the 10Fs in SOT23 packages.
>
>The "product" will be very small (one 10F/SOT23, one SMD LED and
>a few SMD passives, probably just 10x10 to 15x15 mm's).
>
>The two methods I've thought about are :
>
>1. Using a bed-of-nails using "pogo" pins.
>Pro: easier to lay out the PCB. The ICSP-pads could be anyware.
>Con : a bit more complicated hardware setup. Have to make a fixture
>with the pogo pins and probably a couple of indexing pins with matching
>holes in the PCB.
>
>  
>
I've done the pogo pins bit before. No extra alignment posts are needed 
if you make the pads
thru-holes and use the  chiseled probes. The probes are almost 
self-aligning. You can probe from
the top (just holding the probe array), or probe from the bottom in the 
usual way. I like arranging
5 pads on 2mm or 2.54mm centers in a line.

>2. Using contact fingers on one side and a PCD edge connector.
>Pro : Reasonable easy harware setup using a standard connector.
>Con : Have to route the signals to the edge of the PCB and possible 
>have the extra space for the depth of the connector.
>
>  
>
You will have poor results because the contact point pressure is too 
low; if the PCB is not
very clean, or if the surface is slightly oxidized, you can't cut through.

A good way to do this (what I did for Imagic in 198X) was to design a 
test station with the
important contacts taken to the edge of the PCB, like conductive ribbons 
of tinned copper;
when the PCB array was properly inserted, photo-sensors would cause the 
probes to be
forced against an almost arbitrary point on each conductive ribbon. VERY 
fast testing ; 12
PCB's was tested at the same time, with LED's indicating which PCBs were 
OK & which
were bad. We tested and sorted Good/Bad for 12 PCB's in less than 1sec 
each. 

NOTE: Pogo pins have a finite lifetime, usually 10K actuations. Usual 
failure is the internal
springs breaking. This has to be monitored.

>I don't want any additional hardware (connector) directly on the PCB.
>I'm hoping to be able to make a few 100's of these...
>  
>
--Bob

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