I use mostly 0805 parts, though I do occasionally use 0603. I use 1206 when I want to run a trace between the pads, easier than using a jumper. I use a lighted magnifier rather than a scope. Get the best one you can afford since it can also be used for inspection and lots of other things.

When stuffing the boards I usually tin one pad of several parts, solder the parts on that pad, then go back and solder the other side of them all. This cuts down on the problem Harvey notes below wherein soldering the second side results in unsoldering the first side.

Once you get started with smt, you will never go back to through-hole. It's cheaper, easier, faster, and no holes need be drilled if you are making your own pcbs.

Mark

I tin one pad for small parts, touch the pad with the soldering iron tip an use it for a stop.?? Then with tweezers, slide the chip onto the pad.?? Then solder the other end, being aware that the heat on the other pad could transfer over to the first pad and melt the solder there.?? Be quick.

One student I had was employed part time.?? He tried to solder SMT resistors using a set of soldering tweezers to do both sides at once.?? It caused much amusement amongst the other technicians.?? I fixed that by explaining a better method, certainly soldering one side at a time.

On larger TQFP chips, make sure that you solder one pin on one side then solder the opposite side.?? Soldering one side completely can pull the chip out of alignment.

I found a set of anti-static tweezers from Amazon worked well for holding parts.

Harvey


On 10/29/2020 1:01 PM, keith wrote:

For the smaller components I hold them down with a toothpick and tack a couple leads , then solder them

On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote:

???Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

I tin one pad for small parts, touch the pad with the soldering iron tip an use it for a stop.? Then with tweezers, slide the chip onto the pad.? Then solder the other end, being aware that the heat on the other pad could transfer over to the first pad and melt the solder there.? Be quick.

One student I had was employed part time.? He tried to solder SMT resistors using a set of soldering tweezers to do both sides at once.? It caused much amusement amongst the other technicians.? I fixed that by explaining a better method, certainly soldering one side at a time.

On larger TQFP chips, make sure that you solder one pin on one side then solder the opposite side.? Soldering one side completely can pull the chip out of alignment.

I found a set of anti-static tweezers from Amazon worked well for holding parts.

Harvey


On 10/29/2020 1:01 PM, keith wrote:

For the smaller components I hold them down with a toothpick and tack a couple leads , then solder them

On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote:

?Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

For the smaller components I hold them down with a toothpick and tack a couple leads , then solder them

On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote:

?Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

I find that 1206 resistors are good to start with, as well as 1206 parts.? They're not the cheapest (805 and 603 are frequently cheaper).

I use SO outline parts and not TSSOP.? I use metcal soldering equipment and have a binocular microscope (check the distance between the stage and optics, since some are designed for chip inspection and give you no working distance).? Weller 1500 series would work well, but I prefer metcal.

I generally find that 805 works for me, with some 603 as needed. I'm working with 0.5 mm TQFP-100 and TQFP-144 pin chips (FPGAs and video display chips), and find that the bypass capacitors take up too much space otherwise.

Some chips require such small capacitors.

I avoid BGA like the plague, and QFN packages can be difficult to solder to.

Harvey


On 10/29/2020 12:30 PM, Dave wrote:

Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

For the smaller components I hold them down with a toothpick and tack a couple leads , then solder them

On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote:

?Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

Check Mouser Electronics. They usually have what you need and you can get it much faster than eBay and you will know exactly what you are getting!

Sam Reaves

ARS W3OHM

Owner and Moderator of:

LeCroy Owners Group on 开云体育 (Current and Future Group)

Electronics and Mechanical Hardware Design Engineering Manager

Andritz Rolls Global Research Center (RETIRED)

On Thu, Oct 29, 2020 at 12:31 PM Dave <theschemer@...> wrote:

Ok, just a followup on my looking for physically large sized SMT
resistors. I researched yet again and realize that the physical size is
based on the max watt rating, which I already knew (but probably
forgot). And for my first attempts of making SMT boards I want large
sized components for ease or working with them. So using a 0.200 inch? Edited to correct size. :)
length resistor (3/4 watt) where I only need a 1/4 watt resistor is the
only way to do it. So now that I looked at ebay yet again I see I can
get what I need at least in most of the sizes I desire for now.

Dave

Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote:

?Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.

Dave

Dave,

I doubt you need to worry about tin whiskers as a hobbyist... not due to the solder or to tin plated traces or parts. I consider the lower ability to "wet" the connection and higher required temperature for RoHS solder to be the larger drawbacks to using it.

73 de Jim, KB3PU



Received from Dave at 10/29/2020 14:55 UTC:

Jim,

I read about tin whiskers a long time ago but didn't much worry about them as I wasn't making pcb's etc then. I just read about them before you brought them up. I came to the conclusion that the "tin" was the problem and not the solder. After seen some microscopic images it looks pretty wild and plenty of room for disaster. In fact, I bought some Tinning solution but only used it once. I also bought the crystals but never used them. Now I have quickly advanced (with my most basic and useless projects) to getting my boards made. I am waiting for my first order to arrive hopefully next week. :) Then after I really any mistakes or things I should have done different, I will have learned something so it's all good.


On 10/28/2020 12:19 PM, Jim Higgins wrote:

RoHS isn't a requirement that applies to consumers, incl hobbyists who might tinker with the product. It applies only to manufacturers. We - hobbyists - can repair even brand new RoHS compliant gear using tin-lead solder if we want to.

RoHS is an EU thing dating from early 2003 that expanded industry wide because industry wants to do business with the EU. I have no idea how the low/no-lead portion of it was ever incorporated into products made for applications in space... since the problem of "tin whiskers" (Google it) in pure (or almost pure) tin solder was documented back when vacuum tubes were king and solid state didn't exist - in the early part of the 20th century.

We (the USA) have had at least one satellite failure and one nuclear plant malfunction due to tin whiskers. In the case of a satellite - even a big expensive commsat as was the case - it's not really convenient to go up there to fix a connection that's growing a whisker that has caused a short circuit even if the short hasn't caused permanent damage. RoHS solder formulation has improved since those days and conformal coating over completed boards takes care of any remaining risk. Conformal coatings in consumer products make repairs much more difficult.

Jim H

Jim,

I read about tin whiskers a long time ago but didn't much worry about them as I wasn't making pcb's etc then. I just read about them before you brought them up. I came to the conclusion that the "tin" was the problem and not the solder. After seen some microscopic images it looks pretty wild and plenty of room for disaster. In fact, I bought some Tinning solution but only used it once. I also bought the crystals but never used them. Now I have quickly advanced (with my most basic and useless projects) to getting my boards made. I am waiting for my first order to arrive hopefully next week. :) Then after I really any mistakes or things I should have done different, I will have learned something so it's all good.


On 10/28/2020 12:19 PM, Jim Higgins wrote:

RoHS isn't a requirement that applies to consumers, incl hobbyists who might tinker with the product. It applies only to manufacturers. We - hobbyists - can repair even brand new RoHS compliant gear using tin-lead solder if we want to.

RoHS is an EU thing dating from early 2003 that expanded industry wide because industry wants to do business with the EU. I have no idea how the low/no-lead portion of it was ever incorporated into products made for applications in space... since the problem of "tin whiskers" (Google it) in pure (or almost pure) tin solder was documented back when vacuum tubes were king and solid state didn't exist - in the early part of the 20th century.

We (the USA) have had at least one satellite failure and one nuclear plant malfunction due to tin whiskers. In the case of a satellite - even a big expensive commsat as was the case - it's not really convenient to go up there to fix a connection that's growing a whisker that has caused a short circuit even if the short hasn't caused permanent damage. RoHS solder formulation has improved since those days and conformal coating over completed boards takes care of any remaining risk. Conformal coatings in consumer products make repairs much more difficult.

Jim H

Jim,
There is a raft of information on tin whiskers at one of the NASA sites: Some really great (scary) photos

As you can see on the NASA site, there actually were several communications sat failures due to whiskers. The one that most people remember is the Galaxy 4 Panamsat. That is the one that was carrying most of the pager traffic in the US. I worked on equipment that went on the replacement sat. If ever there was a customer that was jittery and over protective about tin, that one was it. He was right!

As to how the tin got onto the sats, you will see several examples of things that were overlooked. "Everybody" knew that the leads on the ICs, transistors and most electronic parts were tin plated, so we had them solder dipped. We went out of our way to make sure the terminal posts we bought were solder plated, or solder dipped. When we inspected some of the terminal posts that looked odd for solder plate, we found that some were tin plated. At that point we stepped up our inspection for the finish, and we found that the suppliers were ignoring the solder requirement, and sending tin finish because they were in stock. Other structural hardware sometimes was tin plated. Several corrective actions were taken to replace them.

Conformal coat does not protect against tin whiskers. The whiskers are really sharp, and push through the coatings. They also take on all kinds of odd shapes, and have been seen to curl over and touch each other. They also can break off, and become lodged in areas that are not coated.

Harvey

_._,_._,_

---

Yes, we're in violent agreement.

Unless you're a manufacturer, RoHS (or whatever your local flavour is) isn't
a problem.

Space vehicles are exempt from these regulations, I guess they figure not
many of them are going to wind up in a landfill. For the tin whiskers, the
problem wasn't lead-free solder, it's the tin plating on the copper tracks,
something even hobbyists do. I think they nickel plate stuff like
spacecraft PCBs now.

Dunno if there is a chemical solution to do nickel plating on copper like
you do with tin, but electroplating nickel is really easy.

Tony

RoHS isn't a requirement that applies to consumers, incl hobbyists who might tinker with the product. It applies only to manufacturers. We - hobbyists - can repair even brand new RoHS compliant gear using tin-lead solder if we want to.

RoHS is an EU thing dating from early 2003 that expanded industry wide because industry wants to do business with the EU. I have no idea how the low/no-lead portion of it was ever incorporated into products made for applications in space... since the problem of "tin whiskers" (Google it) in pure (or almost pure) tin solder was documented back when vacuum tubes were king and solid state didn't exist - in the early part of the 20th century.

We (the USA) have had at least one satellite failure and one nuclear plant malfunction due to tin whiskers. In the case of a satellite - even a big expensive commsat as was the case - it's not really convenient to go up there to fix a connection that's growing a whisker that has caused a short circuit even if the short hasn't caused permanent damage. RoHS solder formulation has improved since those days and conformal coating over completed boards takes care of any remaining risk. Conformal coatings in consumer products make repairs much more difficult.

Jim H

RoHS doesn’t bother a lot of people, even if you’re repairing old gear where the tracks fall off if you look at them funny you’re still allowed to use leaded solder.? They’re full of lead and god only know what so redoing a couple of joints in lead-free isn’t going to save too many whales.

?

It’s not all that complicated, just mainly nit-picking pedantic pen-pushing stuff.? I work in IT dealing with money, so I’m used to that sort of thing.

?

If you making laptops or whatever you get a statement from whom you buy solder, PCB, wire etc from that says how much lead is in it.? You staple all those together and send it off to the EU and say “our laptops are made from this” and everyone is happy.? Of course this means you can’t buy the cheapest solder from Honest Johns Alibaba shop and things are a bit more difficult if you actually make solder, but that’s not most of us.

?

Tony

?

?