Soldering LQFP64-50 package

Is there any secret people use to successfully solder the STM32F4? About half of my boards come out with solder bridges. I can cut down the size of the paste stencils, but I’m worried about open disconnects. Do you guys have any soldermask between pins on the package?

I’ve never soldered one, but I think there definitely SHOULD be soldermask between the pads.

No soldermask between pads on mine…
Is your stencil 100 microns or thinner?

It’s a 5mil thick solder stencil (127 micron)

I use 75 or 100 with good results

Thanks for the advice. I’ll try a thinner stencil!

Are you using a reflow oven? If so, what kind?

Just a cheap Chinese desktop model we got off eBay for a few hundred bones. Are you suggesting there’s a problem with my reflow oven’s settings? I couldn’t imagine what that would have anything to do with.

@ jay - What solder paste are you using? Leaded or lead free, No-Clean or watersoluble. A 5mil thick screen is the right thickness. The openings on the screen, are they 100% to the pads, if so reduce the opening size by 10%.

Leaded solder (I can’t remember specifically what I’m using right now, but I think it’s 63/37). I think it’s no-clean flux in the paste.

The pads have been reduced by 10%.

I’ve never had any problems with soldering, and all the other parts on the board come out beautifully.

I’m using N-sized (nominal) landing pattern (not the high-density one).

I might try shrinking the stencil’s pads for that particular part a bit more.

Any other ideas?

I’m using a pretty hot profile (my stupid reflow oven doesn’t seem to solder all the boards properly if I use a cooler profile for the 63/37 solder), but intuitively, I’d think a hotter oven = better soldering.

@ jay - i have been using cheap and cheerful 63/37 paste up until today.

I sprung for some 62/36/2% Tin/lead/silver fine pitch paste

Glad i did, much easier to use and better results - there is an Octopus out of the cheap and cheerful oven…

Looks great, Justin.

I can’t decide what I want to buy more… o-scope or oven.

If your going to do a few then oven - don’t list to Brett about being a purist and using an iron - remember he’s an Aussie :whistle:

Looks great! I’ll try some nicer paste.

You only need an oven if you’re building lots of boards or soldering chips with hidden pads (BGAs, chips with thermal pads, etc). A scope is way more useful.

Sooooo you’re saying scope this month, oven next month? :slight_smile:

I’d say get whichever you need more urgently. If your design works and you don’t need to debug anything then a scope isn’t going to give you anything except another toy to play with. If your design works and you need to assemble a bunch then an oven will be more useful. If your design doesn’t work and you need a scope to fix it then an oven is going to be useless…

Haha, well, those two things are also in widely different price brackets. You can get a perfectly functional reflow oven for less than $300, but a decent oscilloscope costs quite a bit more than that.

EDIT: I guess I’m seeing quite a few used (but decent) 100 MHz DSOs on eBay for roughly the same price. Never mind! Get both!

Actually, you can get a very good new Rigol 1052E for $329.

I’ve got a couple of those and 100Mhz version. A solid piece of equipment. Excelent build quality.

in AU at least, the DS1052E isn’t being sold in numbers - the 100mhz variant DS1102E is only $80 more (that’s the genuine way to get 100mhz). Although my eyes have been more than a little taken by the DS2072 at a bit over double the DS1102 price ($923 vs $439 inc tax)