Surface mount Stencils

Hi,
Just edging myself into surface mount and plan to make a board featuring at 16pin SSOP chip , plus other through hole bits ( its for a battery manager (LTC4006); only package type available for this ).
The problem I have is not making a complete mess of putting down solder paste and getting a tidy result. I have my DIY oven in a workable state.

I was wondering if anyone knows of or has a solder stencil for this type of chip?

If I could find a mask for individual chips or for a board that has some, that could be aligned to suit ( I could put alignment points on my PCB), then I'd be able to neatly add this device, or make up some nice adapters with chips fitted.

I've looked at the DIY type UV exposed stencils on the net which look a complete disaster.

Ha ha,...

Just noticed Hobbytronics sell such an item !!

This is what I do if I don't have a stencil for an smd chip...

I smear some solder paste in a thin layer with a spatula on a piece of metal/plastic.
Then use the chip as a hair-comb to scrape some solder onto the pins (hold with tweezers).
Each pin of the chip has now a small blob of solder paste on it.
Then just drop/press it on the circuit board.
Leo..

1 Like

Thats brilliant

https://www.bing.com/videos/search?q=soldering+smd&go=Search&qs=n&form=QBVR&sp=-1&pq=soldering+smd&sc=8-13&sk=&cvid=CF09E79836B64475A40A5673A48DBEF1

Some PCB services offer stencil cutting as an extra option.

The problem I've had with solder paste is the shelf life. I don't solder many boards (but they are all SMD) so the solder didn't last from one board to the next.
I have been able to hand solder some pretty small parts, but after reading Leo's excellent suggestion I am considering giving it another shot. Does anyone know of a long shelf life solder paste?

I only use small tubs (no syringes).
If you don't use it (leave it in the fridge) the alcohol evaporates slowly.
One or two drops of alcohol and a stir gets it back to the right consistency again.
If you use it, some of the flux stays behind on the stencil.
One or two drops pushed out of a flux-pen could replace that too.
I use one tub already for more than two years.
Leo..

If I remember correctly your eyes are up in age.

Time to get a microscope, makes things a lot easier. :wink:

FYI

Using the hair comb method and a hot plate with a hot-air rework station is easy.
And less thermal/ESD stress for the smd chip and circuit board traces.
Leo..

1 Like

Sounds interesting will have to try it.


The solder wick method works well too.

I first solder all SMD capacitors, resistors, SOT23s etc. with a hotplate.

Then solder the SMD I.C.s with the solder wick method.

Do you have a favorite?

My ideal would be water soluble as I like my boards clean.

No. The only affordable option here is from China.

I try to avoid adding extra flux, and you don't need as much solder paste as you might think.
My boards look clean from the start, so I rarely clean them.
Leo..

You may not need solder paste. You can get wire solder that is finer than a hair and soldering iron tips to match. If you insist on paste, store it in a refrigerator, warm to room temp before using.
Paul

I've never put paste in a fridge, no problem (I was taught in no uncertain terms than solvents do not go in fridges (explosion hazard), so I'd be very careful to check before putting anything solvent-based in a fridge anyway.)

Have had good results keeping Solder Paste Syringes in the fridge.

Almost 3 years for a T5 syringe and it still works fine.

We put them in fridge for 20 years with no problems. Had separate fridge just for solder paste. What the cool temps do is slow the migration/consolidation of the heavy metal particles to the bottom of the container.
Paul

I have a tub of Chipquik SMD291SNL50T3 which is now over a year old and still seems fine. The datasheet mentions that it is still good past the stated shelf life.

I do keep it in the fridge but I'm confident that there is no explosion risk since the amount of solvent in one 50g tub would be fairly low, the fridge gets ventilated (opened) regularly and if there was a lot of vapour coming off of it it wouldn't last more than a few days before being dried out and useless.

At the rate that I'm using it I'm definitely hoping for a long shelf life...

I have 0.015" solder and a little 0.010" (solid). However it would seem to be easier when soldering some many pin ICs. The refrigerator is a problem, I won't put chemicals in my food fridge.

I think the next time I need solder paste I'll get a "tub". Store if in a cool corner of my basement and hope for the best the next time its needed.

Thanks for all the ideas.

Boy your probably as old a I am :grinning_face_with_smiling_eyes:

1 Like