Disintegrating circuit boards?

[Reed]

I started recapping my Sansui QRX 6001 last night. To my surprise, when I applied heat to pull the old caps off the PCBs, some of the areas on the PCBs where the solder attached the cap to the board actually separated from the surface of the PCB. Solder will not stick to the area vacated by these soldering "rings." Fortunately I have been able to bend the legs of the caps over to the next component in the circuit and complete the circuit that way, but why are the PCB soldering areas coming of the board?

I am using a Radio Shack soldering station that has "low (20 watt)" and "high (40 watt)" settings. I am using the "high" 40 watt setting. Am I using too much heat? Or are these 35 year ld PCBs just beyond their service life and disintegrating due to age?

Any tips are appreciated.

 

[Q8]

I've found that the lower settings on soldering equipment usually works better for electronics. Also age of the board may come into play. Especially if it was ever somewhere extremely dry or extremely humid or both.

 

[Reed]

Thanks. Both my QRX 6001s were eBay purchased and I don't know their history. I will forge ahead on the low-watt setting.

I am treating this first QRX 6001 recap as my learning/practice run. Once I get the hang of it, I will recap my other 6001 using better caps. Better to learn these things on this one.

 

[quadsearcher]

Been there, done that. A temperature controlled solder station is much safer. I set mine to about 750F and use a drop of liquid flux to help spread the heat faster and always use fresh wick. In and out in a few seconds is the key, if you hold a lower heat longer the bond between printed circuit and circuit board breaks down then you get traces of circuit pad on the iron and have to fold the leads over to the next undamaged part of the trace.
Hakko 936 iron, GC 10-4202 flux, .031 solder = ~$100. Undamaged circuit board = priceless.

 

[Reed]

I kept on recapping tonight. Even with my iron on the "low" 20 watt setting I still had a few spots pull off the PCB. It looks like something was spilled in this unit at some point. I can clearly see residue trails across the PCBs. I wonder if that has something to do with why it hardly works anymore and why the PCBs are disintegrating.

 

[Doug G.]

Speed is of the essence and solder wick is not the best in that respect. The best way to remove solder from pads with leads through them is with a heated solder sucker (not the ones requiring the use of a separate soldering iron). They have a bulb on them which you squeeze, hold the heated tip over the lead and on the pad, and release the bulb, sucking the solder up the special tip, which has a hole in it, and up a tube. You can be very fast with this method and not loosen the pads. It's not really a matter of the boards being old. It's just that heat loosens the adhesive and the faster you can get in there and out, the better.

Radio Shack has an acceptable model I use at home. I used to have a more professional model where I used to work which enabled the user to hold the tip at an angle to the board, thus clearing other components but there is usually enough clearance with the straight Radio Shack model.

Believe me, I have used every desoldering method ever devised and the heated sucker is the best.

Doug

 

[Reed]

Thanks! I might pick one of those up before I do my next 6001. I am about 1/3 of the way through replacing every electrolytic capacitor in this first 6001, so I am going to press ahead with what I have and see if it even works. I know I need to make a trip to Radio Shack to pick up some fuses, LED lights for the face panel, and heat sink compound for the transistors on the heat sinks. I will look for a heated solder sucker then.

 

[quadsearcher]

Doug is correct. I tend to forget about those because I'm so cheap. The pros I used to work with swear these motorized ones are even better: http://www.amazon.com/Hakko-Desoldering-Kit-With-808/dp/B000ARPULW and will do multilayer boards. Liquid flux helps with wick, makes it faster than wick alone. Wick does dry out over time, dip it in flux and like new again.

Again, too low of a temperature takes longer to melt the solder which allows the adhesive to work loose.

 

[Reed]

Thanks.

 

[Q8]

I will look for a heated solder sucker then.

Sounds like a slang name to call the Radio Shack employee that runs up to you and asks you what they can help you with as soon as you walk through the door.

 

[Reed]

 

[Doug G.]

OK, I guess I haven't tried the motorized suckers but I can see where a continuous vacuum source would be terrific (no hand fatigue from squeezing the bulb over and over in multi component desoldering).

And quadsearcher's advice is good re wick if you use that. It is important to have fresh wick that is nice and shiny copper and not oxidized. Wick has flux included in the braid but it can dry out or evaporate leaving the copper exposed to the air and resulting in oxidation. Then it will not work efficiently anymore requiring more heat and a longer dwell time on the pad, leading to loosened foil.

Doug