How would you guys solder TQFP208 0.5mm pitch ? - Page 1
Forum section: electronics / repair

author: alpher
author_rank: Frequent Contributor
timestamp: January 25, 2020, 01:28:58 am
content: Hi, in need of some advice, have a couple of this ancient VGA cards out of HP scope.Managed to burn couple of cards already, so decided to fix them by replacing the main chip, a C/T T65550B. It comes in TQFP 208 with .5mm pitch. Somehow managed to solder one successfully but it took many tries and over an hour.Used medium knife T12-K lots of flux and even more patience.Is there a better/easier way ?Have one more to go.Thanks for any pointers.

author: thm_w
author_rank: Super Contributor
timestamp: January 25, 2020, 01:34:44 am
content: An even line of solder paste (dispenser would help), toward the outer side of the pads and hot air would work too.Its more about your preference than anything IMO.I assume you have a microscope?

author: ataradov
author_rank: Super Contributor
timestamp: January 25, 2020, 02:05:21 am
content: Assuming you have a microscope or some sort of magnification, it is not that hard.1. Align the chip on the pads2. Solder one pin on the corner3. Check the alignment and solder a pin on the opposite corner4. Drag solder all the pinsFlux can be introduced at any point, but I like to do it after item 3, it makes the alignment easier.I have not soldered 208-pin packages, but I do solder 144-pin devices regularly and it takes may be 10 minutes after some practice.

author: alpher
author_rank: Frequent Contributor
timestamp: January 25, 2020, 02:20:17 am
content: Don't have a microscope to speak of, use a magnifying glass/lamp.Also don't have any good solder paste let alone dispenser.Was thinking more in line with what ataradov does plus maybe running hot air afterwards just to smooth things out.What do you think?And what type of iron tip would you suggest?Thanks again.

author: ataradov
author_rank: Super Contributor
timestamp: January 25, 2020, 02:26:07 am
content: No need for hot air. If you do it right, it will look fine without it.Tip does not matter, whatever you are used to most likely will work. I use the same Pace 1124-0035-P1 tip for almost everything, including this.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 25, 2020, 02:48:21 am
content: I usually do pretty much as ataradov suggested.If you end up with a few solder bridges after you've drag-soldered all the pins, don't sweat it, they can be removed by adding some flux to the affected pins, then clean the tip of your iron to get as much of the solder off the tip as possible, and gently swipe the tip along the bridged pins, from the IC outward toward the pad, some of the solder will migrate onto the soldering iron tip, removing solder from the bridge. If the first try doesn't do it, clean your tip again and repeat as necessary until the bridge is gone.Also be careful when drag soldering not to apply any pressure, as this could bend the pins out of alignment or damage pads. Let the flux and solder do all the work of transferring heat from the tip to the pins/pads.Lastly, there's no such thing as too much flux IMHO. Sure, you'll have a bigger mess to clean up once you're done, but flux is the magical ingredient that makes the solder flow nicely to where it's supposed to go. Drag soldering only really works with a liberal application of flux.

author: alpher
author_rank: Frequent Contributor
timestamp: January 25, 2020, 02:54:39 am
content: Thanks guys, much appreciated, here's what I have to go with and the result of the first one.Card works fine so far, given that they go for, way over a hundred bucks even today. I think that even 1 hour of my time its worth it.The chip itself can be had for $8 btw.

author: thinkfat
author_rank: Unknown
timestamp: January 25, 2020, 08:49:53 am
content: Quote from: ataradov on January 25, 2020, 02:26:07 amI'd even go so far as saying it's easier with just enough flux and a soldering iron than using paste and hot air:- applying the paste without a stencil is always messy business, especially for fine pitch components. It will always be too much.- if your paste is not fresh, you'll have all kinds of issues with tiny solder balls in between the leads.- QFP packages will not self-align easily, even when using paste and hot-air so there is really no advantage.I've seen people try paste and a soldering iron and it was a big mess in most cases and is best avoided.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 25, 2020, 05:56:04 pm
content: Quote from: alpher on January 25, 2020, 02:54:39 amWho's your source for these graphics "Chips"?They're known to fail on other DSO's too, I feel like getting a couple just in case while they're available.

author: alpher
author_rank: Frequent Contributor
timestamp: January 25, 2020, 07:25:50 pm
content: Quote from: shakalnokturn on January 25, 2020, 05:56:04 pmhttps://www.utsource.net/

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 25, 2020, 10:36:54 pm
content: do you people have to quote the large pictures as well?Quote from: alpher on January 25, 2020, 01:28:58 ami wonder why you have to ask, since desoldering out such large IC, which you did is 10X more difficult than soldering a new one back into place... for your level i guess the better/easier way is... do many more times (practice makes perfect) if you have to ask me what tip? i use $5 temp-no-control normal and cheap conical tip soldering iron to do it...

author: james_s
author_rank: Super Contributor
timestamp: January 26, 2020, 01:33:26 am
content: I've hand soldered TQFP208 parts several times, it's no problem. First double then triple check that pin 1 is in the right spot because it sucks when you do a perfect job and then realize you've got it flipped around 180 degreesThen align it carefully and solder one corner, fine tune the alignment and solder the opposite corner. Verify the orientation again, then add flux and drag the little ball of solder. If you get any bridges use a bit of wick to clean it up. Wash the flux off and you're done. I use a $3 illuminated loupe to verify the alignment but usually I can manage with a naked eye.

author: Miti
author_rank: Super Contributor
timestamp: January 26, 2020, 02:52:33 am
content: In my experience, the best flux for "drag soldering" is the water soluble flux. Wash and air blow it after and you get a perfect, shiny, clean job in 10 min.If you can wash the board, of course.