Suddenly 0.5mm QFN becomes a piece of cake.. - Page 1
Forum section: electronics / projects

author: nctnico
author_rank: Super Contributor
timestamp: June 17, 2013, 09:45:16 pm
content: The past few days I've been putting together various prototypes. This one is interesting. It has a 0.4mm QFN on it. It makes a 0.5mm QFN look like a walk in the park. On the right is the tip I used to solder both chips. The extended pads make it easy to solder these chips by hand. I just add some flux, put solder on the tip and gently swipe the soldering iron along the pads after fixating the chip by soldering a few pads.

author: Dave
author_rank: Super Contributor
timestamp: June 17, 2013, 09:57:05 pm
content: Looks great.How did you solder the large center pad?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 17, 2013, 10:15:00 pm
content: Quote from: Dave on June 17, 2013, 09:57:05 pmUnless it's needed for thermal or decoupling reasons, you can often just leave it unsoldered.An option is to either put a big-ish hole underneath to manually solder, or some thermal vias and leave a hole in the underside resist, so you can paste it using heat applied from below.

author: nctnico
author_rank: Super Contributor
timestamp: June 17, 2013, 10:26:34 pm
content: Quote from: Dave on June 17, 2013, 09:57:05 pmThermal via's like this (if imageshack is working):I use the same tip to let solder flow in 2 or 3 vias and then wait until the solder gets sucked up into the other vias.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 18, 2013, 12:28:23 am
content: QFNs are easy if you have a small heat gun, try doing a BGA if you really want something difficult...

author: westfw
author_rank: Super Contributor
timestamp: June 18, 2013, 05:27:51 am
content: Will a special QFN package created with "extra long" pads for hand soldering end up interfering with automated assembly?

author: Smokey
author_rank: Super Contributor
timestamp: June 18, 2013, 05:33:49 am
content: Quote from: westfw on June 18, 2013, 05:27:51 amThey already make these..... they call them QFPthe pads even stick out the sides like legs(Ill be here all week)

author: poorchava
author_rank: Super Contributor
timestamp: June 18, 2013, 06:14:44 am
content: Quote from: westfw on June 18, 2013, 05:27:51 amYes they may. It generally depends on multiple factors like paste screen thickness, paste particle size, paste bonding agent density, reflow profile and type of metallization on pcb and components.In general the failure mode is excess solder on pads which forms a droplet and makes QFN float. Sometimes the chip will yank to the side and some pads will remain unconnected. It's all about process parameters.

author: nctnico
author_rank: Super Contributor
timestamp: June 18, 2013, 05:16:36 pm
content: Quote from: westfw on June 18, 2013, 05:27:51 amAs far as my experience goes it doesn't interfere. I'm using these footprints on boards which get manufactured by the hundreds.

author: poorchava
author_rank: Super Contributor
timestamp: June 19, 2013, 06:06:45 am
content: It will function most of the time, yes. But in some industries the customer will come to you with a 50k units claim about "wrong shape of solder meniscus, according to this and this and that standard". No experience with avionics or military, but that approach is typical in automotive and medical industry. "100% like in the book or else we don't buy it"