On Thu, Mar 24, 2011 at 1:44 PM, RussellMc wrote: > I'd be interested in comments on practical experience with mechanical > alignment of 5mm through-hole LEDs with and without "stoppers". > > LEDs are to be wave soldered. LEDs may be being machine or hand > inserted. Leads may be being trimmed and bent before soldering, or > just trimmed, or ... . > ... > The LEDs have "stoppers", small protrusions on the leads which > position them about 10mm above the PCB surface when correctly > installed. > ... > LED leads are 0.5mm square so a 0.7mm hole is acceptable but close to > minimum. > ... > > Manufacturer wants to slot board so LEDs sit hard on board and > stoppers are bypassed. I am very resistant to this suggestion as slot > for leads 9about 1.2mm x 0.6mm for 0.5mm square lead) not only is an > invitation to disaster soldering wise, but allows so much mechanical > slop that LED alignment is still not guaranteed. > Your resistance is correct - I would not even start down this path. > > Questions > > 1: Presumably a typical pick and place machine that can handle 5mm > LEDs will also cut and cinch LED leads well enough for them to be > aligned when using stoppers. Yes? > Depends on the machine. Hand cut/clinch is better with a good operator. > > 2. How common is pick and place capability for 5mm LED package? > Probably not very - I happen to use a CM nearby that has a complete leaded P&P system in addition to SMT. > > 3: I'd assume that LEDs wave soldered without cinching would be a > disaster whether using stoppers or sitting LEDs on PCB. > I'd assume that solder wave would tend to push LEDs up and also > tilt them at an angle as the wave passed. Also that some flotation may > occur. > Yes? > Oh yeah! > > 3. If LEDs were hand inserted prior to wave soldering I'd assume that > use of a manual cut and cinch tool would be a minimum in order to > stabilise LEDs from wave soldering process. > Yes? > Yes - IME this has always worked better than any machine for leaded LED alignment. > > Based entirely on circumstantial information it appears that the > manufacturer MAY be using manual insert, trim without cinch, wave > solder. > If so I'd like to change that to include either auto insert with cut > and bend or manual cut and bend. > If you need the LEDs spaced off the board, then you can cut the leads above the stoppers and use nylon LED spacers or the kind that dissolve when the board is washed after soldering. > > Any other thoughts welcome. > If LED alignment is really critical, a custom built alignment fixture may b= e necessary. If you use a proper fixture, then running the board with LEDs not cut or clinched should work well. Vertical location as well as X & Y position would be determined by the fixture. > > > > > Russell > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .