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PCB Through Hole Size for Lead Free

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#52367

PCB Through Hole Size for Lead Free | 7 November, 2007

Hello all, we are having issues with some specific package type aluminum caps we use while running lead free. We used to run these leaded with none of these issues. Basically we are not getting more than 25% hole fill on these parts. I have tested different thermal settings and flux settings with no luck. I believe the hole size needs to be enlarged. Currently the lead diameter is 77% of the hole diameter. Is there a recommended IPC spec that would have this info I need? I can approach engineering on this but they will not be very receptive without standards. Id like to enlarge the hole so the lead is only 50%-60% of the hole diameter.

Thanks in advance

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#52396

PCB Through Hole Size for Lead Free | 8 November, 2007

I have not seen hold size as an issue when switching Sn/Pb to Pb Free wave soldering. Trying increasing your dwell time in the wave- typical for Sn/Pb is 2 to 3 seconds. Try 5 seconds to see what you get.

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#52399

PCB Through Hole Size for Lead Free | 8 November, 2007

Hole size may not have been an issue for you because your holes were already big enough? The alloy you are using has a lot to do with this I believe also. We are already at 5 seconds dwell for this which is mfg recommended for our solder. The caps we see this problem on have .030" diameter leads with a .039" diameter through hole in a .062 board. That doesn't leave much room for turbulence of the wave to enhance wicking... We have no issues at all with components that have smaller lead to hole size ratios.

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RDR

#52402

PCB Through Hole Size for Lead Free | 8 November, 2007

60% ratio would be great start. that is what we typically shoot for with all leaded for the most part.

25 mil diameter in a 40 mil hole, works great for auto insertion as well

Russ

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#52409

PCB Through Hole Size for Lead Free | 8 November, 2007

Josh: Your 0.009" [0.228 mm] clearance should be fine. The minimum clearance should be ~0.008" [0.20 mm].

Is the 0.039" [0.99 mm] the measured or the expected hole diameter? While we wouldn't like it, we wouldn't be surprised to see 0.008" [0.20 mm] tolerance on holes that size.

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#52411

PCB Through Hole Size for Lead Free | 8 November, 2007

Did the PTH barrel ends in massive copper clad ? If yes this type of poor thermal layout topside heating is often recommended.

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#52412

PCB Through Hole Size for Lead Free | 9 November, 2007

We design and assemble PCB's and use a min of .015 thou over the component lead diameter without incident but if your component pad is in a copper mass either top or bottom this can create other problems especially if you don't have top heating as the above poster stated, good luck.

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#52422

PCB Through Hole Size for Lead Free | 9 November, 2007

Thanks for all the great suggestions guys. We do not have topside heating but topside temps are where they should be before hitting the wave. No excessive copper in the area either. We are going to start with the most problematic board and use it as a test case and go from there. Im going to say .020" clearance is the target with a .015" min if necessary.

DaveF... where are you getting the info of .008 clearance should be the minimum? Is there an IPC spec? I already have IPC-2222 on order if thats the one...

Regards JD

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#52433

PCB Through Hole Size for Lead Free | 9 November, 2007

Try raising the part off the board a little. I bet this will help.

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#52440

PCB Through Hole Size for Lead Free | 9 November, 2007

Are you thinking for the soon to be displaced air to be able to escape out the top? Raising components wouldn't be ideal from a process standpoint.

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#52446

PCB Through Hole Size for Lead Free | 10 November, 2007

Josh: 2222 will meet your requirements. 2221 is a companion to 2222. So, if you're going to try to get your engineers to follow an accepted standard, you might need both. Although, they probably already have both and are just playing dumb with you.

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