PCB Repair Procedures & Techniques

[Mark Black]

Ran across this today and just wanted to share:

Circuit Board Repair and Rework Guide

To be sure they would like you to buy some of their rework products, but the guide is free for the viewing and has lots of great info.

[kblues]

Thanks for the great link. Just what I've been looking for to make a repair on a pcb for a pedal I have been working on.

[jrfrond]

Something NOT mentioned on this site, and that a surprising number of tech do NOT know about is low-melt solder, sold as Chip-Quik and also offered by Zephyrtronics (my source, because it's cheaper). It is one of THE easiest and most effective ways of removing SMD and/or large components from PCB's. The solder, which is a tin/bismuth alloy, and flux is applied to a joint soldered with standard electronic solder (RoHs or Non-RoHs, no difference) and alloys with the original solder, lowering the melting point to somewhere near the boiling point of water. So, as long as you keep ALL joint on the component as hot as boiling water (quite easy to do), you can just lift the component off or out of the board, as the case may be.

Though we have two Pace vacuum desoldering units here in the shop, low-melt solder figures heavily into everyday life for us, as we use it to achieve the near-impossible. Also great for those can caps soldered to chassis.

Seriously, if you haven't used or heard of this stuff, you need to check it out. We've been using it since the late 90's and it's a Godsend.

[Mark Black]

Hey John thanks for bringing up the Chip-Quik. I've never used it myself, but then again my need to desolder complex surface-mount stuff hasn't been common so far (usually 8-pin at most). Do you use it for some through-hole as well?

I'm curious too - do you have/use the associated "air-bath" system shown on the Zephyr website? That looks fairly slick if it works as advertised.

[jrfrond]

Hey John thanks for bringing up the Chip-Quik. I've never used it myself, but then again my need to desolder complex surface-mount stuff hasn't been common so far (usually 8-pin at most). Do you use it for some through-hole as well?

I'm curious too - do you have/use the associated "air-bath" system shown on the Zephyr website? That looks fairly slick if it works as advertised.

No, we don't have that system. It would be nice to have, but it's a heavy hit. Currently, we don't replace any BGA-type IC's.

Low-melt for through-hole can sometimes work wonders. Let's take, for example, a standard pot soldered to a double-sided PCB. You can either wrestle with Solder-Wick, and not get all of the solder up, and hence, possibly lifting the hole plating out if you force the pins out of the PCB. Or, you can go to you desoldering unit (if you have one), change the tip to the right orifice size, wait for it to warm up, and then hope that you can grab all of the solder with THAT. You might need to crank up the heat on the desolder tip, which might compromise the glue on the traces. OR, you can use some low-melt to bridge all of the pins, heat it for a few seconds, and the pot will pop right out. This is just one example.

Just want to mention that you need to use an RMA paste flux with low-melt to get it to work. The Chip-Quik kits come with it. I purchase the Zephyrtronics Low-Melt in bulk tubes, and purchase the flux elsewhere (Howard Instrument Corp.). Of course, this flux comes in handy for other rework procedures as well, such as wholesale reflow of multiple suspect solder joints on a PCB.

Even if you DO have a desolder unit, AND have the fancy tips to remove flatpacks of all sizes, it's worth it to note that low-melt absolutely minimizes the chances of PCB trace damage, due to the low melting point as well as the lack of physical contact with a huge desolder tip.

A linky for y'all: http://www.zeph.com/lowmelt.htm

[km6xz]

I have been using Chip-Quik for years, before it was called that and everyone I demo it for, regardless of how long they have been removing parts from boards is amazed. It pays for itself many times over in reduced damage to reusable parts, pc boards and traces and speeds removal of hard to remove parts, such as those with heatsinking or ground-planes on multiple layers. Surface mount SO14 for example come off cleanly, start to finish in 2-4 seconds. I have rework stations gathering dust because they are more trouble than their worth quite often and require regular maintenance of the vacuum pumps.
One tip, use very little of the low temp solder, it is easier to clean up and more does not speed anything up. The Chip-Quik is one of the reasons I prefer working on SMD over through hole and point to point. When we were doing dozens of Behringer 19" units or mixers a day, it reduced work time to test, diagnosis and replace, say, a 4580 on the vertical main board in all of 10 minutes or less from start of disassembly to final assembled performance test.
Over the years it likely has earned an extra $50,000 in time savings.

[Mark Black]

Well the thought of it making things easier with heavily-sinked parts is definitely intriguing. I just did full filter cap replacements on a Crest CA9 and CA12, and those had so much copper around the component leads I had to use my Weller station jacked up to 800 degrees and with a big tip right next to my desoldering gun to get enough heat in there to melt the solder (let alone free-up & bend the leads straight).

Reason I never tried the Chip-Quik is I always thought it was kind of expensive for the amount you get - might have to invest in some after all.

[jrfrond]

Reason I never tried the Chip-Quik is I always thought it was kind of expensive for the amount you get - might have to invest in some after all.

Well, it is. That's why I purchase the Zephyrtronics Low-Melt. It's cheaper. 32ft. is $147.95.

[km6xz]

The solder is expensive but you only notice the cost once, after using it it becomes as essential as your solder station and you factor in the $.05 cost per IC or pot removal compared to saving 10 minutes and possibly a pc board. Another way it saves is that now you will not throw away replaced pc boards. When we started doing Behringer for example they had no parts department and had no clue what parts ever were. John and I were left to our own devices to figure out parts sources and equivalent characteristics. Also few if any schematics. The low temp solder meant we had a mountain of spare parts in units that had been replaced by Behringer to the store or customer. Being able to remove a pot or switch, or processor from a bad junker unit and having the part undamaged and looking like new was the next best thing to having all the original parts. Lots of those dead units were disassembled to removed the boards which were labeled and cataloged. When a tech needed a part that was not in normal inventory, he knew exactly where to find it on a surplus board, in the same location. If anything it sped repairs a great deal because 95% did not need to be put aside to await parts. When we took over Alesis service when the factory closed its own shop, we were flooded with a similiar situation, with hundreds of units coming on on pallets every week, mostly large boxed units like keyboards, ADATS, mixers and speaker. Parts were a real problem again but Chip-kwik filled in just fine. When we started supplying reworked rotary head to other shops, there was a frequent problem of a small SO video amp inside the head that needed to be replaced. It became a 10 second operation.
We had expensive rework stations but we stopped using them because they took more work, time and training for the techs to accomplish a less effective less safe operation.
So, really, how much was that worth to us? We would have paid 10 times as much and still been ahead in profits. The first time a big gullwing chip or a 4 gang pot is removed from a heavily heatsunk multilayer board in 30 seconds and have an undamaged board AND component, you will forget about cost.

[jrfrond]

The solder is expensive but you only notice the cost once, after using it it becomes as essential as your solder station and you factor in the $.05 cost per IC or pot removal compared to saving 10 minutes and possibly a pc board. Another way it saves is that now you will not throw away replaced pc boards. When we started doing Behringer for example they had no parts department and had no clue what parts ever were. John and I were left to our own devices to figure out parts sources and equivalent characteristics. Also few if any schematics. The low temp solder meant we had a mountain of spare parts in units that had been replaced by Behringer to the store or customer. Being able to remove a pot or switch, or processor from a bad junker unit and having the part undamaged and looking like new was the next best thing to having all the original parts. Lots of those dead units were disassembled to removed the boards which were labeled and cataloged. When a tech needed a part that was not in normal inventory, he knew exactly where to find it on a surplus board, in the same location. If anything it sped repairs a great deal because 95% did not need to be put aside to await parts. When we took over Alesis service when the factory closed its own shop, we were flooded with a similiar situation, with hundreds of units coming on on pallets every week, mostly large boxed units like keyboards, ADATS, mixers and speaker. Parts were a real problem again but Chip-kwik filled in just fine. When we started supplying reworked rotary head to other shops, there was a frequent problem of a small SO video amp inside the head that needed to be replaced. It became a 10 second operation.
We had expensive rework stations but we stopped using them because they took more work, time and training for the techs to accomplish a less effective less safe operation.
So, really, how much was that worth to us? We would have paid 10 times as much and still been ahead in profits. The first time a big gullwing chip or a 4 gang pot is removed from a heavily heatsunk multilayer board in 30 seconds and have an undamaged board AND component, you will forget about cost.

Amen to all of that Stan! Yeah, those early Behringer days were quite frightening, because they were still caught up in the mentality of their old Samson-distributed regime, which was a nightmare I lived for over a year when I managed service there.

In addition to what Stan said, if you price out a fancy rework station with all of the tips and trimmings like a Pace PRC2000 (we have one which was purchased before I started here in '95), which is around $5K+, and divide that by the cost of the Low-Melt solder, which will be SO much more effective and less time-consuming, you will realize that the Low-Melt is the MUCH better alternative, and that you can then spend only about $500-$700 on a very basic vacuum-desoldering system. You would essentially be throwing away over $4K+, because the fancy rework station will be relegated mostly to basic through-hole desoldering on double-sided PCB's.

[babysgottheblues]

Hey Thanks guys for all the great links and info! Can't have too much knowledge. Knowledge is Power. I'm fixing to embark on my first 8 pin chip pull. I'm taking out a chip to install an IC Socket so I can try out a few chips to see how I like their different sounds in some guitar effect circuits. Guess you guys have messed with those little 8 pin chips at one time or another. I bought an IC Inserter & Extractor Set (6-40 Pin DIP) to help but have never pulled a chip so do I just use solder wick or my solder sucker as I have no work station to use? I use $100 a roll Cardas Quad Eutectic Solder to solder all my parts in my boards as I do it all by hand and almost never pull anything, so this works fine for my hand built boards. Any help is greatly appreciated!

[J M Fahey]

You guys made a bell ring in my head.
It's wood's metal or some close alloy ... or better said, "incomplete" wood's metal, which becomes so with *your* tin/lead solder.
For a general reference on them: Wood's metal - Wikipedia, the free encyclopedia
For the price of 1Kg of it : Woods Metal Alloy 1kg Stonecarving, Woodcarving, Modelling, Sculptor supplies, Tools, Materials-Alec Tiranti products
*Very* affordable £35.40 Inc VAT per Kilo.
I'll check whether I can find it in Argentina and, did I tell you that a solder wire maker not only is my customer, but wants to trade a 2x12" speaker cabinet for equivalent $$$ in solder?
Mmmmmmmmmmmmmmmmhhhhhhh !!!! , you give me ideas !!!
U$S 125 for 32 feet? No way José.
Thanks for the hint.

[km6xz]

Wow, that is a great bit of information.
But it is dangerous containing Cadmium and lead but according to Wikipedia a non-toxic-vapor low temp alternative is available:
"Field's metal, or Field's alloy (named after Simon Quellen Field) is a fusible alloy that becomes liquid at approximately 62 °C (144 °F). It is a eutectic alloy of bismuth, indium, and tin, with the following percentages by weight: 32.5% Bi, 51% In, 16.5% Sn.
As it contains neither lead nor cadmium, it is a non-toxic alternative to Wood's metal. It is used for die casting and easy prototyping."
Find out if that is available from you solder wire maker friend. You might have stumbled on a lucrative business opportunity. Since it used in casting and fixing iron work into stone, and used in casts of sculptures, this city must be crawling in it. I'll ask a sculptor I know here about it.
I notice the electronics stores here feature soldering above all else, even the smallest shop has dozens of specialty solders and 20-50 different flux on the shelf. I never figured out what some of them are for so maybe its time to find a tech or assembly specialist who can explain it in English because my Russian does not include much technical or chemical terms. My language skills are fine for chatting up a girl in a club but not reading technical research papers;>) I do have my priorities;>)

[J M Fahey]

Yes. I mentioned Wood's metal because this is the "famous" one, but I was really interested in the topmost alloy, with *only* lead, tin, and bismuth.
That would be the least exotic of them all, and still good for our purposes.
I've already sent an email to http://www.cordes.com.ar/index.php?m...er&idf_mater=9 , a local "any metal you wish" supplier; don't know if they deal in less than 1 Ton amounts though. They refer to many alloys, including a 47ºC melting point one, which they sell for fire safety sprinkler heads.
I asked price and delay quotes for a 1Kg ingot.
Of course they might be laughing their 4ss off at my request !!!
My customer has a small , family operated solder wire and bar factory; I'm sure he could put this ingot in his machine and put out 1 or 2 Kg of real low temperature rosin core solder wire.
He's coming next week with 4Kg solder wire, a 1 or 2 Year supply for me, as part payment for a 2x12" cabinet for his son, who already owns one of my heads.
Never actually seen the process before, I think I'll pay him a visit.

[Steve Conner]

I'm sure I've seen the guys over at 4hv.org make their own low melting point alloy for this purpose. I think bismuth is the main ingredient, maybe they used a hint of gallium too.

I've never tried the stuff before, but we deal with SMTs a lot at work, and you have me sold on it. I'm no chemist and somebody else is paying, so I'll just get the commercial stuff.