So The blog ate my comment, thanks! =P
This isn't (I think) the exact app note I was looking for, but it is close enough.
http://www.ti.com/lit/an/slua271a/slua271a.pdf (http://www.ti.com/lit/an/slua271a/slua271a.pdf)
This app note has the profiles discussed on IRC, JEDEC STD 20.
It is important to note that the preheat and ramp down are multiple-purpose.
1: It decreases the high temp, solder flow time
2: It normalizes thermal expansion, both in the chip and in the chip to board connections.
A appropriate demonstration is maybe cold water on a hot light bulb, common failure for a mechanics drop light.
Figure 1 shows the internal lead, and we all know any picture with that color scheme means really really small =D
Sorry about the blog, ian did install some kind of cookiemonster on the new server :) I guess it is very hungry.
Thanks for sharing this link, it is very informative!
I did some preheating on the vid, but not as extensive and the right temperatures as described in this apnote. Due to cutting the movie it looks like it was just a few seconds, but the whole soldering (the hotair part) took about a minute.
Could you tell the settings you use to solder QFN?
Brute force! I still solder in the dark ages, It is the only way with a 35(?) watt Radio Shhack.
The custom tip is the only thing note worthy. I really hate the round pointy bits. It is now a diamond like or screw driver shape, _/ the angled sides are flat .81mm or so. It has to serve multiple functions or I'd have gone smaller.
I would not solder anything I really liked, eg not easily replaceable, and not get some practice warm up on something else directly before hand. It doesn't turn out well using "dark-age" method. Some of it's best work doesn't "show" well, the parts they replace burnt the board pretty bad looks like my fault.
I did notice the preheating, I noted or thought "it was too close too long and something started to flow". There maybe time lapse altering the audio, the air sounded jet like. In fact there is one point you see a/many solder balls leaving the area.
Please don't think you did bad, I loved it! My comments are just comments.
I'm thinking reflow plate is the cheapest dyi method for things you can't get at with iron. This will be my approach, 2nd hand hotplate, or toaster with fire brick. I know these work. I believe the only difference between the home built manual timed ones and the big fancy commercial ones are the software, insulation, and above all cost. The first two issues can be solved with time and effort, and they are a large portion of the cost aside from R&D and scale.
Perhaps a nice ebay pencil and the open sourced iron drivers.
I'm open to comments :)
I'm interested how to easily preheat the board and chip. I guess you need some kind of stand/fixture to hold the hot-air handle and keep it steady on the board. then you could adjust the temperature without juggling hot parts too much :) Any suggestions here?
If there is interest I have many scrape boards and desoldered chips (also QFN/DFN) of which I don't have a public datasheet. It was fun desoldering these chips (kinda a form of therapy ;)). I can send them to the DP PCB store. I see there are still some left of the last batch I send to Ian.
Something like a wood bending jig maybe. Have you seen these. It is a tube on two cross braces, they feed steam in the back.
Let us build a pseudo hardware..
Inner and outer shell:
2 Coffee cans Large and Medium
Or 1 Medium Coffee can 1 soup can
Centering/Stand-off device:
1 soup can.
Some amount of fiberglass type insulation, Foil wad may suffice
Lid:
Pie tin, Aluminium foil, Another flattened can.
Heater:
Paint stripper, Air wand, Charcoal fire?
Heater stand:
Soda pop, Soup cans,
They create a cradle when crushed. Use two crushed into cradles for paint gun. for Air wand same or cut cradles in the tops.
Wire coat hangar, if the heater is light enough or enough are used.
Proceedure:
1: Cut three sided rectangle/square in bottom of inner can, leave flap for airflow adjustment and direction tuning.
2: Cut entry hole in the large. You can choose direct flow or Circumferential(I swear i didn't invent that word)
a: For direct flow enter the bottom of the outer can, off-center for adjustment purposes, with a hole sized for heater
b: For circular flow, enter the side near the bottom. Large cans can fit the paint gun here, small cans might not leave enough PCB space.
3: Put on leather gloves, or get band-aid ready.
a: Cut third can length wise, if you have one, into three nearly even concaved pieces.
b: Cut three small strips from these cutting across the short side about a finger width from the top, these will be feet later
4: With some luck the larger strips will wedge the inner can.
a: Place the outer can long end on the table.
b: place two braces inside the bottom, left and right of center
c: place inner can on braces,
d: separate the braces so the can looks centered.
e: Wedge third/last brace at the top.
F: If it doesn't fit force it, if it's sloppy increase the dish in the braces.
5: Feet/Anti roll device
a: bend each foot pieces into a V, now fold down the ends like to make a M. Should look like _A_ with out the middle brace.
b: I'm getting lazy get the screw gun, rivet gun, or work out the H tabs and slots.
c: Attach feet,
6: Using "poking device" of your choice, stuff insulation down the sides. The primary goal is to fill the bottom, so the hot air chooses the easy path.
a: "Flake" the fiber glass into sheets, and cut strips (hand width)
b: Wrap several folded strips (fold short length, 1-2 times) on the bottom of the inner can. Medium taunt. Test fit until close fit.
c: Add 1 layers of tight wrap, folded 3-4 . We want a slip fit. "Strip C" loosens and lets the inner stuffing expand.
D: poke it with a stick! Gently at first. The smaller tight wrap lets the upper portion slide over it some. After one circle of tamping, add more stuffing until you run out get bored or it is full.
7: Cap it off, some origami foil work is in order here. And is left largely to the artist. It shouldn't be a tight fit just a restriction, and easy to remove.
8: Adjust air flap.
a: Side feed shove it to the bottom of outter with a bit of twist. Picture a car ramp in large parking structure.
b: Bottom feed, the flap is a baffle in this setup, Adjust to reduce air speed. Perhaps a crease in the center to stiffen it.
That maybe lost some coherency between the brain and keyboard, The feet and flap adjust ments need consideration before the stuffing.
Lol, I forgot this was open here. Hope I was done