joeft wrote: > I have found similar info as what Steve has noted. Many vendors > are letting their parts automatically "roll over" to lead free > compliant versions. This means that if you manufacture something > now (during the transition) you will have a mix > of RoHS and non-RoHS compliant parts.
In fact, a lot of parts have been manufactured for years without lead. Thing is, you don't know which ones because the manufacturers will not give a guarantee in writing. But, they will tell you _verbally_ that they are lead free - A lot of good that does. > Some will solder better > than others depending on your assembly shop's process. And you > might find this leads to extra documentation overhead should > someone want to know what your compliance status is down the road. > Lead free solders will be mostly tin with a small amount of other > metals (usually bot not always silver), and they will indeed require > higher soldering temperatures. Board materials and plating will have to > change if you were using HAL, as Steve points out. Many shops will > not have gold available as a plating option however and will use > matte tin instead. This brings into play the "tin whisker" problem > which it seems not everyone has solved yet. Research that has been done recently indicates all metals (Including gold) used in PCB manufacture can grow whiskers. See: http://nepp.nasa.gov/whisker/other_whisker/ Even so, we have never been bitten by whiskers. We think (But, how do we really know?) this is because the manufacturing lines that have done our assembly are _very_ clean. all of the valid literature regarding whisker reduction emphasizes cleanliness (Which makes sense when you think about it). > Gold does not always > solder as well as you might like since it can actually diffuse out > into your solder. Unless your shop uses some really bizarre fire-retardant, > the plating should be the only board material problem. One note on part > compatibility - watch out if your are using certain plastic packaged ICs > (QFP, QFN, some BGAs). The higher solder temperature profiles can exacerbate > problems with moisture. Some parts manufacturers already require a "bake out" > for certain parts. When you go to the higher solder temps required for > lead-free soldering, the "moisture sensitivity level" can increase by two > levels (usually from MSL 2 to MSL 4). This means your pre-loading handling, > moisture exposure, and bake out may have to be changed. Be sure to ask > whoever places and solders your parts how they deal with this issue. We had a bad experience due to moisture - As far as we are concerned, baking is a must. > I regards to what you need to put on the drawings - I suggest contacting > your vendor(s) and ask them exactly what wording to use to get the process > you want. And then make sure they label the finished boards with date codes, > UL file numbers etc. so there is some traceability or record of what they did. > > Joe Regards Marvin
