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Pad size and soldermask expansion questions for RGB LED footprint

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amaningd:
Hi everyone,

I'd like to add this Kingbright 5mm RGB LED (WP154A4SEJ3VBDZGC/CA) to a PCB that I'll have fabricated with JLCPCB.  The recommended hole layout consists of four 0.9 mm diameter holes spaced 1.27 mm apart.  I've attached what I have so far for the footprint. I usually add a few tenths of a mm to the pad diameter around the hole to give someplace for the solder to flow, so I made the pads 1.1 mm wide. JLCPCB lists a solder mask requirement of 0.038 mm (1.5 mil), so I rounded up the Solder Mask to 0.051 mm (2 mil).  But now there's only about 0.051 mm between each pad's solder mask expansions, and JLCPCB's minimum solder mask bridge is 0.1 mm. I've also tried a pad size of 1 mm, which gets me a 0.152 mm gap, but I wasn't sure about the pad size being too small compared to the hole.  What's the best way to handle this?

Thanks!

Kean:
I recommend keeping the solder mask gap as large as possible.  The pins on these will easily bridge during soldering, and can be a bit of a pain to rework.  When soldered into a plated through hole, they should still form pretty strong solder joints even if the pad is somewhat smaller.  Using oval pads will provide a bit more surface area.

I have used similar 5mm RGB LEDs in a client product, except I used the QT Brightek QBL8RGB60D0-2897 which is pretty similar spec and pinout.  Pin numbering is reversed vs the Kingbright datasheet but I believe they are actually drop-in equivalents.  A little dimmer, but noticeably cheaper.

My drills are 0.65mm with 1.0mm wide oval pads, and 1.27mm spacing.

The CM I work with actually asked me a few months ago to increase the spacing between the holes as they are seeing too many solder bridges.  I think they are using automated lead forming, hand insertion, and selective wave soldering.  I have now increased the 1.27mm (50 mil) spacing to 1.52mm (60 mil) as I wasn't tight on space.  The new PCBs arrived just before the holidays, so I will be assembling some samples this week but a quick checked showed that they still insert quite easily.

For the 0.5mm square leads (per DS) I maybe should have gone with a 0.75mm or 0.8mm drill, but I have not see any issues there.  I've hand soldered hundreds of these, and the CM also hasn't mentioned an issue for mass production other than the bridges.  Pretty sure the pins on the leadframe are not perfectly square, as a quick measurement shows 0.5mm square but just over 0.6mm on the "diagonal".  It is possible that the Kingbright may not fit my holes - not sure if I have any to hand to test...

amaningd:
Kean, thanks for the recommendations!  I was so focused on whether it was fab-able that I kinda forgot to think about the part where I hand-solder them... I've increased the lead spacing to 1.52mm / 60 mil. One other question: how critical is the solder mask expansion value?

thm_w:
JLC spec is 1.5 mil so you can use 1.5mil.

You can use less but the pad might get covered up, which could cause problems. Or they might just modify your design anyway.
Oval pads would help as recommended above, then you can expand the pad and guarantee a good connection on at least two sides.

tooki:
I also immediately thought that oval/oblong pads would be a wise idea here. You could also stagger the holes slightly, moving e.g. pins 1 and 3 up a little bit, and 2 and 4 down a little bit. The pins still fit in a row, but you gain a bit of distance between pads. See https://www.eevblog.com/forum/eda/zig-zag-pad-spacing-for-self-clamping-connector/ for what I mean.

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