Reflowing pcb boards?

[CT Jim]

Assuming a board needs reflowing, as in now nothing works, is it better for hot and fast, or low and slow using an adjustable soldering station?

 

[Dingman]

I'm all about hot and fast.
I have no data to support my opinion, even temp measurements can be controversial here, LOL.

But my theory is that if you can get in and out in 5 secs or less, even with small components, the heat transferred is minimal.

Plus, I find some larger, older globs of solder really need that high heat to get them to melt.

 

[Hyperion]

I never reflow entire PCB's as I think you can do damage by doing so with little or no reason. I clean boards and inspect all the joints with a watchmaker's eyeglass, and resolder joints that don't look good. (maybe 2 or 3 joints per board). Sometimes I'll remove all the solder from a joint and add new, sometimes adding paste flux if needed, hot and fast is good.

 

[elnaldo]

In a large board, I do things like this, so I don't miss any point:

I prefer hot a short time. PCB traces don't like heat for long periods. Many components datasheets specify 10 seconds as max soldering time.

 

[Binkman]

On avg. ss typical joints hot and fast. 680F w/chisel point as most do. Find it just as easy to suck off the old solder, typically takes me about 1 second to solder new joint. I dip tip into brass mesh after every joint.

 

[Goldie99]

Assuming a board needs reflowing, as in now nothing works,

Agree completely with John - I'll clean everything, and selectively re-solder, usually removing old solder from any suspect joint, and re-doing it.
Re-flowing a non-working board may or may not help at all, I'd be aiming to find and target the fault(s), rather than a blanket re-flow of everything.

 

[Hyperion]

On avg. ss typical joints hot and fast. 680F w/chisel point as most do. Find it just as easy to suck off the old solder, typically takes me about 1 second to solder new joint. I dip tip into brass mesh after every joint.

I don't see a joint in that picture that I would personally call ideal, but it's a reasonable illustration of some of the soldering issues seen on PCB's, others:- blow holes, poisoned joints.

 

[NAD80]

The first "OK" needs redone with flux. Not enough solder around the joint to flow correctly. The second "OK" has a bit too much of solder.

 

[CT Jim]

The question comes from a receiver which fell about two and a half feet and no longer powers up.
Been slowly checking points but have not found the issue yet.

 

[Binkman]

2.5 feet is more than enough to deflect a main board to the point of cracking so I'd be looking for solder traces with dmm, Check any pcb ground screws, wire connectors etc.
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I see nothing wrong with the two 'okays' and it is a photo. So why don't you 'experts' post a pic of your 'ideal' good joint(s) by hand and not solder bath flowed.

 

[gslikker]

If I put pictures of my own, I always show compnent side only, for a reason.
But the first OK one looks bad to me also (read: that bad it could be open circuit/cold joint).
This also applies to the too much solder ones, since the result can not be seen....

 

[Dingman]

I have to agree with no re-flowing everything. I've never found a board that needed a total re-flow. I do however, find many cracked joints like this. This did affect output, BTW.

And crappy joints from factory, like this...




And from a cheap chinese batter charger - can't believe this one..


LOL, how about a box elder bug that kept my home A\C from working - (now I'm far far off topic, LOL)

 

[txturbo]

FYI.. A bit off topic but related.

I have been cleaning all of the old flux off boards as I do restorations. I clean the board using denatured alcohol and a stiff PCB brush. It's really easy if you can get the board out of the unit. I put the board in an old cake pan and soak it for a short time in the alcohol, hit it with the brush, rinse and repeat until the board is clean. I then blow it dry with compressed air. Some equipment has too many wire wraps to make removal of the board practical. In this case I use the denatured alcohol in a squirt bottle. I position the equipment in a way that allows me to use paper towels to collect the run off. I then squirt the board, hit it with the brush and rinse with the squirt bottle, change the towels. I then hit it with a bit of compressed air, this rapidly dries the old flux so you can see where the flux is left on the board. I keep at it till the board is clean.

A clean board makes it much easier to inspect solder joints and makes the restoration look better.

 

[EngineerNate]

I do hot/fast. Higher temp gradients with a restricted time of application means less heat transfer up the leads to the components. You want the heat in the solder not the component. I use ~700F most of the time. Solder sucker, clean tip with brass mesh, reapply kester 44.

 

[That70'sShow]

An IPC-A-610 book off of ebay is about $25 not bad to have around for reference. If you use flux (unless it's no clean flux) you want to clean off any residue afterwards.

 

[EngineerNate]

An IPC-A-610 book off of ebay is about $25 not bad to have around for reference. If you use flux (unless it's no clean flux) you want to clean off any residue afterwards.

Good to know. I've never found a need for more than the flux in the core of my solder. Could be that's because I use the good solder or mainly work with new work as opposed to reworking old stuff.

 

[gslikker]

2.5 feet is more than enough to deflect a main board to the point of cracking so I'd be looking for solder traces with dmm, Check any pcb ground screws, wire connectors etc.
------
I see nothing wrong with the two 'okays' and it is a photo. So why don't you 'experts' post a pic of your 'ideal' good joint(s) by hand and not solder bath flowed.

It is very possible to have at least something "reasonable" and one must when doing a lot of joints, as just one being open can be enough to blow up an amp.....

I replaced an ic on a almost 30 years old circuit card from an old system at work, today. (yes there is such stuff around, still operational)

(This is done having ONE GOOD EYE ONLY due to rectina surgery a month ago, still leaving some macula problem at one eye giving distorted sight. First soldering thing since 3 months..)

As the pins were bent on solder side I had to cut every pin on the ic, and take it out one by one.
The finished-pic of the IC itself shows the flow is not 100% through to the top side of the card, but everything makes contact and it works.
I just did a two seconds flow using the soldering iron because the tracks are sensitive for loosening from the old card. Tracks for power 3 seconds, maybe.
The finished picture is before cleaning off the residu after soldering.

I am not getting paranoid when it looks a little "lesser" but once soldering you easily get the feel if flow is good enough or not.

Now this is a one time attempt but people soldering every day will very soon have the feel of how long exactly it takes to have the joints all look the same.

Good to know. I've never found a need for more than the flux in the core of my solder. Could be that's because I use the good solder or mainly work with new work as opposed to reworking old stuff.

Yes old stuff can be a real PITA.

 

[That70'sShow]

Good to know. I've never found a need for more than the flux in the core of my solder. Could be that's because I use the good solder or mainly work with new work as opposed to reworking old stuff.

Even the flux in the solder can potentially be corrosive if left without cleaning depending on the type of flux in the solder. I personally haven't seen it happen, but it must happen to be included in IPC training