| We are all faced with increasing interconnect density in all we do. This means smaller everything, especially components and that which they are mounted upon but, hopefully, without smaller minds and thoughts. It all demands more process control and evidence of quality effected by it. Therefore, I am again off to seek better ways, and forums, to ensure quality through more effective process control so we don't react to defect without it. | | Go get 'em folks. | | Earl Moon (MoonMan) | MoonMan
Yeah! Things advance. The first PCBs I had to deal with (in 1954) were on SRBP with, believe it or not, rolled copper foil (electrodeposited copper foil was an invention of the Royal Mint in England c. 1955 and was initially made on polished stainless sheets as a batch process). The line widths and spacings were c. 3 mm and the copper came off even if it saw molten solder 1 m away. Do you know how we made them? They were printed in a plate offset machine with a sticky ink on which we hand sprinkled an asphalt powder (dragon's blood) which we fused in an oven. Etching was initially done in nitric acid, quickly replaced by ferric chloride after a guy was poisoned by NO2 fumes. For prototypes, our photoresist was fish glue sensitised with potassium bichromate: exposed to the sun for three hours, developed with hot water. Those were the days (God forbid!)!
Now we have HDIS with 25-50 �m vias and I have even seen an experimental circuit with 15 �m track widths and spacings, 2.5 orders of magnitude finer than our original ones. It has been a very hard job to keep up with progress in our industry and, after only one year's semi-retirement, I'm beginning to feel it all slipping past me. The rate of change is alarming.
But don't abandon us here, Earl, in your seeking new pastures of green information. Your advice and wit will always be appreciated.
Best regards
Brian
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