clear flux under 1206 resistor

The difference between 1 oz and 2 oz is only 1 mil or so, not a lot. It would take a lot of plating.

Just more solder paste would float the part up a bit.

It would be interesting if someone made paste with built-in spacers.

Or high-ohm surface-mount resistors with spacer balls. LTC added spacer balls to their LGA bricks to stop shorting. We complained about shorts, they said it was our fault, then they added the balls.

John Larkin wrote in news: snipped-for-privacy@4ax.com:

No, it would not. The surface tension of the solder will suck it down to the pad, AND the result MAY only be a mil or two higher off the board. My method is proven. It merely requires hand placement, but that is not unusual in HV or applications where very low leakage currents are expressly required. My method results in over a half mm ride height and finished placement.

Phil Hobbs wrote in news:peq7hp$q9n$ snipped-for-privacy@dont-email.me:

Only if the solder has someplace else to go. Otherwise it'll have no choice but to lift the part. Of course if you use too much, it can do a Kilauea and slide off to the ocean.

Seems like a lot of work just to avoid putting in a slot, which our vendors do for free.

Cheers

Phil Hobbs

Everyone had trouble with the LTC micro bricks. I have never used them and when I asked my contract assembler what to do to improve my boards for manufacturing they say never use an LTC part! lol

Rick C.

By "my method" you mean the solder bumps? What exactly is that? Are you talking about a high temperature solder that doesn't melt when the parts are reflowed with a lower temperature solder paste? I'm not picturing this.

Rick C.

Since when doesn't the solder have other places to go? The nice curved fillet is likely the first thing to absorb excess solder, bulging and no longer meeting spec.

Rick C.

Which will lift the resistor.

Cheers

Phil Hobbs

Yep. We had this happen with the central pad on a QFN. Until the stencil aperture was reduced the QFN got lifted up on the central blob of solder, usually losing contact along one edge.

As you say a slot is the way to go of course if at all possible.

you have to use way too much for it to lift the part, normaly those concave fillets that form show that the solder is pulling the part onto the board.

maybe if you put copper under the nonmetallic part of the resistos with enough excess solder you could float the resistor on the solder.

no added cost, is not exactly the same as for free.

That isn't the point. Dipping in an ultraound tank just dilutes the flux in the larger volume of iquid; ultrasound (nanobubbles) is what gets under the parts, but removing the now-diluted flux/water solvent is what gets it away from the board.

You can easily dilute 1000:1 in each rinse, and removing 99.99% of the solvent+flux, after the dip is ten times as effective as removing 99.9%. Three tanks at 99.99% removal is better than leaving a part per billion of the flux in place.

You have three untrasound tanks? And you monitor the water quality in each?

We have a water-wash system that does successive washes until the water impedance hits some setting, then it bakes the boards dry.

But we don't use it for leakage sensitive boards, or for certain parts.

What do you use for leakage sensitive boards?

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@googlegroups.com:

That is because you are a dopey f*ck. Hand placed parts are done AFTER all other operations in the HV realm.

You sound like an elementary school playground meaah meaah with your "what exactly is that".

Was I supposed to reply "I'm rubber and you're glue"?

How about "get a basic clue." Yeah... that's the line for you.

Now make up another retarded scenario, putz.

I worked in HV power supply manufacture and design for years.

Rosin flux and solvent cleaner. The board gets dunked in boiling solvent with a deflux agent for a minute, then sprayed with distilled solvent with a wand. It's lifted slowly out of the tank so the expensive solvent flows back down. It's done one board at a time, and requires a person to be there for a couple of minutes, so it's more labor intensive than the batch water wash.

Thanks. I'm familiar with the solvent cleaner. I had one when I did my own pcbs. They were amazing.

I forget what the solvent was. I wonder if methanol might work. It is quite cheap, available at any hardware store. I pay about CAD $11.00 for 4 litres.

Here's a Youtube video on making your own rosin flux:

He uses isopropyl alcohol, but that is expensive and difficult to find here. I tried methanol, and it seemed to work, but I couldn't find pure rosin on ebay. The stuff that was claimed to be rosin was very poor quality. So the results were not good. But it showed that methanol will dissolve rosin flux, so maybe it can be used for cleaning pcbs.

I make my own distilled water, starting with plain water purified by reverse osmosis:

The purified water is extremely cheap at a local water store. It is very good quality, and measures around 11 microsiemens using a pure water tester. My distilled water comes to about 1 microsiemen, which is adequate for silver electrolosis. But ordinary purified water may be good enough for rinsing pcbs.

There is another water store here, but the quality is not nearly as good. It measures around 30 microsiemens and is much more expensive. So you need a good pure water tester to check the water. These can be inexpensive. I use a HM Digital COM-100. I think I paid CAD $40.00 for it new. The readings compare very well with a Hanna 98308 which I use for backup. In no way is a cheap TDS meter adequate for this work.

The HM Digital site is

A single ultrasound dip can dissolve the (viscous, sticky) flux that holds solder paste together. One ultrasound tank, two wash tanks would work. One ultrasound tank with multiple inner tubs (lower 'em like baskets) would do, too.

I haven't washed PC boards for years; my cleaning tasks are more like getting tungsten particles out of boron carbide, monitoring progress by looking at the tungsten L edge on a spectrum of bromine K absorption ... finding a trace of flux in rinse water might work easiest if you could add a dye, because even pure water has some conductivity.

An uncertaintly exists in the nature of the contaminant; if it really is on the surface, in wetted spaces, the ultrasound tank will disperse it into solvent, but if ions move into the epoxy or solder mask, they can emerge days after the washing is done. After the molasses flood, Boston had an aroma for decades so we know the rainfall didn't remove it in the first few years.

The self-ionization of pure water gives a resistance of about 18 megohms per cm, or a conductance of 5.55e-2 microsiemens. About the best distilled water you can buy in grocery stores is about 0.5 microsiemens. The slightest contamination will quickly raise this, so you should easily be able to detect any ionic residue from the flux.

Can ultrasonics reach into the tiny gap between the smd component and the pcb?

Ultrasound can go through the pcb and components just fine; we get power transmission through a human skull, for instance, even at higher frequency. It's the cavitation in the water, though, that does the work, and that happens preferentially near surfaces (because of reflection condition), so one would expect agitation of the solvent to be effective next to any flux deposit.