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Guard Ring on SC70-5 Footprint??

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ChicagoTom

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I have an voltage follower buffer amp with a very low input bias current (AD8627, 250fA), and I would like to place a guard ring around the inputs to protect from leakage current. Due to space constraints, I have to use the SC70-5 package.

What is the best way, if any, to place guard rings around the +IN pin for this package? Placing traces between V- and +IN is not possible due to the small package size.

Thank you in advance!

**broken link removed**
 

As you use it as buffer, I'd recommend to connect the GR to OUT A :
21_1299166735.jpg
 

Obviously, you can't place a guard ring in this case. If low leakage currents are an objective, use a different package, or at least conformal coating.
 

Would hot glue be a conformal coating? Or some sort of silicon for potting?
 

The first point is to clean the soldered board thoroughly. From household chemicals, I prefer methylated spirit. Then dry it.

Clear lacquer, as used for wood or metal (solvent, not water based) should basically work as coating. It's important, that the space between the pads is wetted by the lacquer to prevent moisture from invading the critical zone later on. The coating should be allowed to dry suffcient slowly.

Thin silicone or epoxy resin would work too. Silicone must be free from acetic acid, e.g. special types for electronics coating. Epoxy (e.g. araldite) gives a very durable encapsulation. Unfortunately it would be nearly impossible to repair the circuit after applying it.
 

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