To bend or not to bend...leads?

[Phrazemaster]

Hi all, I'm not sure this goes here in the brewery but I couldn't figure where else it fit.

The question is, when stuffing PCBs, is it wise to bend the leads prior to soldering? I have been doing this as a matter of practice, as it makes for a nice and secure component and good solder joint.

However

I recently needed to lift the leg of a resistor on a build to test it, as I couldn't read the resistor code. I had bent the leads on the resistor when soldering, and even though I used a desoldering Hakko station, I ruined a couple of pads and traces. The bugger was so stuck in there I almost couldn't remove it even if there was not solder in there at all!

I was then thinking, maybe it makes more sense to leave leads unbent, so future removal efforts would be easier. But then, harder to secure it for soldering purposes.

Any thoughts on this?

Thanks,

Mike

 

[scott2000]

I know when I was working on an older adda, the caps had all of the leads bent. Big pita and had to be real patient....

but, it looked like an automated process had done it. I can't see how anyone could've gotten them so close to the board without a hammer and punch.....

Actually have seen a couple of boards like this come to think of it.....

Wonder if there's a tack of some sorts people use.... I know I've heard of using tiny bits of poster tack on smd chips....

 

[xaxxon]

The whole point of bending the leads is to prevent the part from falling out when the PCB is held upside down with components unsoldered. Factory produced boards have that done prior to wave soldering.  If you have something that's very light, like a signal transistor, don't bother to bend the leads. Only bend them when necessary. There's no greater electrical connection whether they're bent or not bent.

If you're trying to lift a lead, I would suggest using copper solder braid and your iron to remove the solder (most of it - not critical).  Then use a dental pick (from your dentist or Harbor Freight - sorry my European friends - don't know the equivalent there) by heating the wire and using the pick to gently pry the component lead loose. You'll use less time heating the lead and will likely cause less if any damage to the board.

PM me if any of this is unclear.  I've been doing this stuff next to forever.









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[Gene Pink]

If you're trying to lift a lead, I would suggest using copper solder braid and your iron to remove the solder (most of it - not critical).  Then use a dental pick (from your dentist or Harbor Freight - sorry my European friends - don't know the equivalent there) by heating the wire and using the pick to gently pry the component lead loose. You'll use less time heating the lead and will likely cause less if any damage to the board.

Good advice. Let me add to it. 

Some boards have the components "stapled" in with an anvil underneath, like a paper stapler. What I do, just heat the joint with iron in one hand, and with the other, quickly stick a very small jeweler's flat screwdriver into the solder puddle and under the lead, twist to lift the lead. With a couple bites, you can get the lead up at a 45, all within a few seconds, preserving the pad. Then go after it in a more conventional way.

For assembly, just bend the leads apart a little bit so it won't fall out.

Gene

 

[Phrazemaster]

Thanks Gene and Xaxxon for the advice; good thoughts.

Where it seems really tough to me is when the solder has flowed up through the back of the board to the top of the board pads - essentially using the via as a conduit so both top and bottom of the board are actually soldered. Even with the solder sucker/desoldering station this has ruined some pads for me...what about this situation?

I like the screwdriver, and the dental pick, tricks. Thanks.

Mike

PS also on  a recent lifted pad/trace situation, I gently tamped the pad/trace back down even though it had lifted, and proceeded to solder the component anyway. I wasn't thrilled with the connection but my DMM showed 0R between the component and the next component on the circuit. So I don't know if you guys go ahead and run a wire under the boards in this case, or trust the fix is "good enough" since the DMM shows  conductivity.

Thanks guys!

Mike

 

[madswitcher]

Hi all, I'm not sure this goes here in the brewery but I couldn't figure where else it fit.

The question is, when stuffing PCBs, is it wise to bend the leads prior to soldering? I have been doing this as a matter of practice, as it makes for a nice and secure component and good solder joint.

However

I recently needed to lift the leg of a resistor on a build to test it, as I couldn't read the resistor code. I had bent the leads on the resistor when soldering, and even though I used a desoldering Hakko station, I ruined a couple of pads and traces. The bugger was so stuck in there I almost couldn't remove it even if there was not solder in there at all!

I was then thinking, maybe it makes more sense to leave leads unbent, so future removal efforts would be easier. But then, harder to secure it for soldering purposes.

Any thoughts on this?

Thanks,

Mike

Hi Mike,
The way I do it to avoid that problem is, before inserting the component, bend the leads to the correct length between the holes and insert it into the board on the component side.  NASA suggest using a cocktail stick to get the correct angle on the bend 

On the solder side, bend one of the leads over so as to keep the component steady in place then solder the unbent lead.  If neccesary,  use  a finger on the bent lead to hold it in place while soldering.

Then unbend the other lead so it is upright and then solder that.  You should then have no problems taking it out at a later date.

Hopefully I have explained that clearly.

Regards

Mike

 

[Scodiddly]

I bend just a little, enough to hold the component in place while I solder.

When it comes to removing difficult parts I'll sometimes just cut all the leads between the component and board, and then remove each lead by itself.

 

[JohnRoberts]

For cheap passive components just cut the component off the top and leads will usually fall out when heated.

Bend or not??? depends on you personal needs. Kind of academic at this point since SMD is taking over the bench. I can't even buy through hole versions of some new ICs.

JR

 

[pucho812]

We use something like this at work. It makes it easy to prep parts when stuffing PCB's that are through hole.  You bend the leads anyway so might as well. As far as having to fix issues,  I have found  that it is easy to cut them out, then remove the lead.This works well for IC's and other multipin components, just cut it out and remove a pin at a time. I tried chip quick  for that stuff and had mixed results as to how easy it was to remove the IC, at least I didn't damage the PCB.

https://www.youtube.com/watch?v=VWTlA5Iz7X4

 

[madswitcher]

I have found  that it is easy to cut them out, then remove the lead.This works well for IC's and other multipin components, just cut it out and remove a pin at a time. I tried chip quick  for that stuff and had mixed results as to how easy it was to remove the IC, at least I didn't damage the PCB.

+1 for this. 

I was always taught that if you have a chip soldered into the board and you are convinced that its is faulty, it has to come out anyway so make it easy on yourself.  Cut the pins on the component side as close to the board as you can, heat up the leads on the solder side and gently pull them out with No72s (British Telecom talk for small, thin long-nosed pliers).  This then leaves you with a nice clean hole to either use a proper de-soldering tool or de-soldering braid.

With multilayer pcbs do it this way even if the chip is just suspect (as long as you have a replacement that is)

Oh and  be careful with those hand-hand solder suckers as they are quite viscious and easily lift the track.  To make it less so, slide a silicon rubber sleeve over the end of the PTFE sucker head and use it at a slight angle so you suck some air in as well as the solder when triggered.  This also saves wear on the PTFE  heads. 

Cheers

Mike

 

[abbey road d enfer]

Where it seems really tough to me is when the solder has flowed up through the back of the board to the top of the board pads - essentially using the via as a conduit so both top and bottom of the board are actually soldered. Even with the solder sucker/desoldering station this has ruined some pads for me...what about this situation?

I use a biro pen tube to blow the solder out. Much more efficient than a desoldering iron, because of much higher air pressure and help from gravity. Just make sure the underside is protected against solder projections.

 

[Mbira]

+1 for bending leads.  I always was taught as a guitar amp tech that you want to have the part secure without solder.  Then The solder is just there to make sure that what is already secure stays secure.

 

[JohnRoberts]

+1 for bending leads.  I always was taught as a guitar amp tech that you want to have the part secure without solder.  Then The solder is just there to make sure that what is already secure stays secure.

Actually back in the 60's I took a mil-spec soldering course in connection with a Navy project I was working on... The official word is that solder can not be depended upon for a reliable connection so there has to be a solid mechanical connections first, then solder.

But that was several decades ago... modern SMD components are so light that solder is more than adequate to hold them in place.

FWIW the mechanical connection rule, still applies for PC mount jacks and connectors. Solder is plastic and will deform over time with repeated mechanical stress... the connectors still need mechanical support.

JR

PS: Back in my through hole days I had a pair of clippers that would crimp over the leads while clipping... but that was so last century.

PPS: Back in the 80's at one of my businesses we had work stations for stuffing TH PCB that had a foam rubber clamp that would hold the TH components in place when you turned the PCB upside down to solder... It worked well enough for mostly flat PCB.

 

[madswitcher]

Hi again,

It would appear that NASA agrees with the Navy - see the enclosed pdf 

The enclosed guide also has a neat way of holding wires while tinning etc: it is a coil spring help above a vice and you press the wire to be tinned into the spring coils in order to hold it while working - neat

Cheers

Mike

 

[JohnRoberts]

Hi again,

It would appear that NASA agrees with the Navy - see the enclosed pdf 

yup....

The enclosed guide also has a neat way of holding wires while tinning etc: it is a coil spring help above a vice and you press the wire to be tinned into the spring coils in order to hold it while working - neat

I remember having a hot wire stripper on my bench for melting insulation off wires, useful for stripping teflon insulation that could be difficult.

Cheers

Mike

Despite being mil-spec certified since the 1960s, decades later while working at Peavey I was forced to take a remedial (introduction to) soldering course with every other supervisor, when it was revealed to upper management how many supervisors didn't know how to solder, despite directly supervising people doing it for their day job.

I was not allowed to skip the soldering class so I kept my head down so I didn't get into a silly argument with the instructor over some trivia and fail out.  Reminds me of taking metal shop class in my senior year of HS after working in a real machine shop for my summer vacation job the previous summer.  :

JR

 

[Mbira]

Actually back in the 60's I took a mil-spec soldering course in connection with a Navy project I was working on... The official word is that solder can not be depended upon for a reliable connection so there has to be a solid mechanical connections first, then solder.

But that was several decades ago... modern SMD components are so light that solder is more than adequate to hold them in place.

Pretty hard to bend the leads on SMD parts. ;-)

 

[Phrazemaster]

Hi Mike,
The way I do it to avoid that problem is, before inserting the component, bend the leads to the correct length between the holes and insert it into the board on the component side.  NASA suggest using a cocktail stick to get the correct angle on the bend 

On the solder side, bend one of the leads over so as to keep the component steady in place then solder the unbent lead.  If neccesary,  use  a finger on the bent lead to hold it in place while soldering.

Then unbend the other lead so it is upright and then solder that.  You should then have no problems taking it out at a later date.

Hopefully I have explained that clearly.

Regards

Mike

Thank-you Mike, I liked that suggestion. Thanks everyone for the thoughts.

I especially appreciated the suggestion of using the desoldering tool at an angle; you guys just saved me some boards!

 

[JohnRoberts]

Pretty hard to bend the leads on SMD parts. ;-)

You can but they typically break apart.  8)

JR

 

[PRR]

> NASA agrees with the Navy

The vast majority of NASA tech admins came from the military. The several services had very similar standards and practices, probably dating to war-time when production and maintenance had to be streamlined thus unified. "JAN" is Joint Army Navy standards. Air Force was Army through WWII.

 

[Andy Peters]

Pretty hard to bend the leads on SMD parts. ;-)

Hmm, you've never lifted the lead of an SOIC or SSOP device off of the pad, and then tacked a wire to the lead?

The best rework I ever saw was many years ago -- a board in some military thing had a large QFP device and a bunch of leads on one side were all lifted off of their pads and an 0402 SMT resistor was put between each pad and the corresponding pin. I guess they realized that series termination was required ...