I don't know what frequencies you are working at... But, The 'prudent' approach would be to proto the boards and have your supplier make 2 or 3 different 'flavors' of surface finish approaches for your assembly people to populate and then test them for performance issues. Immersion Gold works very well, Immersion silver also, so does OSP and white Tin. ALL of them are sensitive to environmental and handling issues and some of them are incompatible with certain processes or environmental conditions... but all of them can be overcome by setting up procedures to deal with the issues. None of them is a solution to all problems... but they all have their special applications for solving issues with assembly and manufacturing of the boards. HASL is a good finish... it's just not real flat. If you have very fine pitch parts, it may cause you some trouble with coplanarity of the leads to be soldered on Quad flat packs or BGA's. OSP works and is flat, has a shorter shelf life less than a year more like 6 months, and needs to be individually wrapped in sealed poly bags to protect it on the shelf until assembly. Gold works and is flat, solders well, and as long as the plating is not too thick it doesn't present a problem... down sides are if the plating is too thick it can embrittle the solder joint through gold contamination of the solder and some issues with 'black pad' occur if the plating process isn't kept clean. Good thing is it doesn't oxidize. Silver solders well, is flat and needs protection as it tarnishes or oxidizes but the oxide it makes is still conductive... in fact silver is the best conductor, better than gold in most cases... Tin also is very flat, and there is some promising work that has been done with tin finishes, Florida Cirtech did some work with White Tin that seemed very impressive. Realize that you are only flashing gold or silver or Tin or OSP on the surface and so little of it is present just to protect the copper surface until soldering is done... After soldering is complete we really don't care what happens to the plating, our solder joints are good. Just a little food for thought... after all the choice you make will depend on the type and complexity of the board you are manufacturing... and how it is handled before soldering. Good luck. Bill Brooks - KG6VVP PCB Design Engineer, C.I.D.+, C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 Datron World Communications, Inc. _______________________________________ San Diego Chapter of the IPC Designers Council Communications Officer, Web Manager http://dcchapters.ipc.org/SanDiego/ http://pcbwizards.com -----Original Message----- From: Wenger, George M. [mailto:[log in to unmask]] Sent: Wednesday, June 15, 2005 2:33 PM To: [log in to unmask] Subject: Re: [TN] RF board finishes Martin, The use of nickel or ENIG is not necessarily a "no- no" for RF circuits. If your RF products have long strip lines than your designers may not want to use PCB traces that are plated with nickel. When you start using many small size discretes and fine pitch IC packages many people have found that HASL is not a good choice. From a soldering standpoint ENIG or immersion silver should work fine. Because of the brittle solder joint failure that have been associated with ENIG we decided to use immersion silver for all of our PCBs. It has been a good choice for us and we've not had any reliability issue since 1997. Regards, George George M. Wenger, Andrew Corporation Reliability / FMA Engineer Base Station & Subsystems Group 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Martin Butcher Sent: Wednesday, June 15, 2005 5:15 PM To: [log in to unmask] Subject: [TN] RF board finishes Hi All, We are currently assembling an RF product (first time build) that utilizes several fine pitch devices, leadless fine pitch devices and a great many 0402's. The board finish is currently HASL and as the volume ramps up there is concern that defects related to the fine pitch and HASL will result in unacceptable costs. We prefer to use ENIG as a surface finish for non-RF products that fit this Bill. I seem to recall reading something on this very Net that mentioned nickel or ENIG being a no no for RF ccts. I am not an RF guy and would love to get some feedback as to the effects of various board finishes on RF products. Perhaps even recommendations as to a "good" finish that will give better yield than HASL. 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