2017 Spring Break

Works Closed

29th May-2nd June

Printed circuit board Manufacturer, Photoplotting Established 1964  All types of Pcb, surface mount sm, PTH, SS single     single sided, PTH, IMS, ML multi layer printed circuit board  prototypes. Cheap high quality PCBs Printed circuit boards. 

Printed circuit boards tooled up from Gerber,JPG,DXF,and most common file types, or camera ready artworks either 2:1 or 1:1 std scale.

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Silver :-
 
Silver is a widely used surface finish for surface mount PCB's. Its relatively cheap and works well during surface mount assembly. Although PCB shelf life is very poor, somewhere in the 3-6 months range, dependent mainly on storage and the condition of the working solution used to apply it. PCB's that have exceeded their shelf life normally sill look the same, unfortunately an intermetalic layer will have formed at the silver copper junction. In extreme cases a small tap has resulted in all the surface mount components dropping off, in less extreme cases dry joints result. If multiple heat excursions are used to assemble a mixed technology board, it's highly advisable if the boards have been stored to fully assemble a sample first.        

Silver is another traditionally banned metal for our industry, but when used in a thin layer the risk of whisker growth is supposedly small. One of it's biggest downfalls is the rapid risk of surface tarnishing, it only takes a splash of tap water containing chlorine or even simply been handled without protective gloves. Very often an OSP style coating is also applied on top to protect the silver, which with the recent developments in OSP does raise the serious question as to quite what the silver is actually there for? Best answer is probably cosmetics, having made the ROHS leap we still want everything to aesthetically look the same as before. 

It's best to always have full solder masking so that the no exposed  silver coated areas remain after assembly. A recent good example of a bad application using silver was a car Key Fob, it's once bright battery connecter pad had turned jet black and turned from conductor to insulator.  

Please note P & M Services recommend prompt assemble if this surface finish is used. If boards are to be stored for any reason before assembly keep them tightly wrapped interleaved with acid & chorine free tissue paper in a cool damp free environment. 

Many thanks to Macdermid for the Storage and Handling data sheet essential reading if you plan to specify this finish.   

Oddly enough eventhough silver is supposedly a green and ROHS compliant, it is a most unwelcome element in our trade effluent stream, as dating back to it's mass use in photographic and surface finishing industries only small amounts are known to poison the good bacteria in sewage works. From a manufacturing and environmental perspective we advise skipping the silver + OSP and using just OSP, as a longer circuit board shelf life and greener environment result.     

 

 

 
 
 

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 Rev  25 April 2017

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