Solder Pad Sizes

Hey, thanks for the answer, it is really helpfull. It was more focused to a solder lap but we also use through holes on other pcba.

When you say you solder wires at a pitch of 1.5 times the Outter diameter of the insulated wires, you mean the OD of the wire with the jacket? or the strands combed together? oh, and the 1.5 times is for the width of the solder lap pad?

We will be soldering only cables to pcba. no SMT as we are mostly a manual assembly factory.

the PCB supplier should have data on the solder pads strength and at which pull strength the pad will tear off with via holes it depends more on the solder type/quality before you tear the wire off

I concur with Just an Engineer(GA to you).

You haven't mentioned to which of the 4 IPC classes of board you are constructing, 1C, 1, 2 or 3. Being in Mexico Class 1C (Class 1 China) isn't a relevant class for you to aspire to. Is this board for domestic class 1 or commercial/industrial class 2 or 3? This will also have a bearing on the design of the board

Also for consideration will it be manufactured with RoHS (or equivalent) materials? As the various lead free solder has different properties which will affect your assembly processes as well.

Another area you should look at is "Is my new board testable"

This thought should be see in the early stages when the board is still in CAD design.

You want the PCB to be manufactured by some company, then every product 100% tested before it lands on your desk, the last thing you want is 10-20% failures cause it wasn't tested.

Can every net be tested (not on to the component leg but a special land)

Single or double sided testing

will you allow enough space on the top to counteract the probe forces acting from the bottom side of your PCB.....

I like the way you think! DFT (design for testing) :) I will look up on this.

Its my job, for the past 11-1/2 years, I have designed test fixturing for the electronics industry here in Australia and New Zealand.

The latest being for a brake lighting manufacturer in NZ, but we have done work for sheffen in Qld (well close enough to Qld..)

Just thinking aloud really:

If you are going to solder the wires into through holes then I wouldn't worry about strength, just make sure that your clearances are enough to avoid shorts.

If the wires are going to be attached to pads, then: in my experience of actually working (i.e. no experience of design or specification) with these sort of things, the quality (spec. method whatever) of the adhesion of the copper to the board seems to be more significant than the pad size.

Which takes me to another question: How much space should I give around the soldering area for manual soldering operations.

How much space from each solder pad and from other components?? I try to give as much as possible but no less than 0.8mm ... and there are still shorts on the soldering process.

The quality of the adhesion of the copper I think it is a very important factor, I will look up on that.

by the way... what happens to the early worm?

I'm no expert on this but 0.8 mm is definitely enough, have you got a solder resist layer?

..and there are still shorts on the soldering process..

Is there any way to get the people doing the soldering to "own" more of the process. If they get to see their own mistakes they ought to start improving.

by the way... what happens to the early worm?

Um, I think the implication is that it gets eaten by the early bird. (Alfred E. Neuman was that guy with the big ears on the front of MAD magazine)

what is a solder resist layer?? what does it look like? is it like a white marking around the pad? I have had that question for quite some time...

early worm still gets eaten hmm... its better to be the bird in every situation hehe

The people who make your blank PCBs will know.

From http://en.wikipedia.org/wiki/Printed_circuit_board

Solder resist

Areas that should not be soldered to may be covered with a polymer solder resist (solder mask) coating. The solder resist prevents solder from bridging between conductors and thereby creating short circuits. Solder resist also provides some protection from the environment.

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From http://en.wikipedia.org/wiki/Solder_mask

Solder mask or solder resist is a lacquer like layer of polymer that provides a permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder from bridging between conductors, thereby preventing short circuits. Solder mask was created primarily to facilitate wave soldering used in mass assembly. The solder mask is most often applied with a green tint but is available in a wide variety of colors and finishes. It also provides some protection from the environment.

Solder mask comes in different media depending upon the demands of the application. The lowest cost solder mask is epoxy liquid that is silkscreened through the pattern on to the PCB. Other types are the liquid photoimageable solder mask (LPSM) inks and dry film photoimageable solder mask (DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to provide openings in the pattern for parts to be soldered to the copper pads. DFSM is vacuum laminated on the PCB then exposed and developed. All three processes go through a thermal cure of some type after the pattern is defined.

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I did a google search for:- wiki solder resist

Results 1 - 10 of about 83,200 for Wiki solder resist. (0.28 seconds)

http://www.google.co.uk/search?hl=en&q=Wiki+solder+resist&btnG=Google+Search&meta=&aq=f&oq=

Looks like a lot of other useful links.

The information is too good to understand the PCB's soldering and soldering masks. Thanks

Go to website Cutler-Hammer, look for "design.pdf". On page 31 you will all your questions answered about pad size in relation to hole size for double sided as well as single sided PCB's. Drill 2 holes, slightly bigger as the insulation of the wire you using, in line with your solder pad. Feed your wire through one hole than back again through the next and solder in pad. Cheapest and most effectful strain relief. Regards, Dieter

where is this document? I can't find it...

Hello Guest,

could not find the design.pdf on the cutler-Hammer website (eaton electrical). Which country website are you referring to?

maybe it is this one ? Link

Anyway i was wondering Manufacturing Jedi, what is your job exactly? because it strikes me odd that you don't know what a solder resist layer is when you are designing something. or is your factory mostly assembly work?

You got me. I meant to say we are designing, the design team is composed of electrical, mechanical, manufacturing etc etc. I am a manufacturing engineer and apply the design for manufacturing principles.

Also please remember that my primary language is spanish and somethings are named different. I knew solder mask but not solder resist layer... sheeshh, cut me some slack here.

Don't get upset, none of us knew your background.......stay cool!

Your English fooled us into thinking that you were first language English, a compliment!

it was just a question. It puts things in perspective i hope the link is useful to you.

I know the most important sentence in Spanish "un Cervesa por favor" and some swearing words of course (everybody should learn foreign swear words they'll come in handy ).

Whenever possible I recommend using a connector on a board instead of just soldering single conductor wires to a board. This will distribute the mechanical load to multiple solder connections, some of which will not have a signal on it. I do recognize that there can be valid reasons to not use a connector though.

yeah, I like connectors also but they are too expensive. we are trying to cut down on costs and 30 to 40 cents is a lot of money from the unitary cost of our product.

This sounds like a penny wise and pound foolish concern. If you only look at the cost of the raw material, then you should be using copper ore, sand, and crude oil. When you include labor costs, the cost of a technician hand soldering a wire will easily be more than 30 to 40 cents per wire.

But you're now delving into the art of design. Deciding which corner can be cut to improve profit and marketability versus which cut corners will just make you bleed.

Have Fun!

I think it depends on where your production is... in mexico I really doubt labor cost can keep up with material costs.... if you consider we take 20 seconds to solder a cable and an operator costs 3 dollars an hour... that means that we spend around .016 dollars in that operation VS having a connector that costs 30 cents (including the one on the pcba) and also having to connect it (4 seconds) which costs you .003 dollars...

Ofcourse there is scrap costs and quality costs but we can manage those with a good control over production processes.

1 cent over a 1Million a year production = 10000 dollars a year

25 cents is a quarter million . A lot more I make a year :(

It would be very different if I was in europe where production labor cost is like 20dlls an hour...

A 20 second operation would cost you 11 cents!!

I once worked for a company that went crazy/happy if someone saved 10 cents on a PCB production, even though it cost us 10 dollars more to replace in the field....

Seen it time and time again.....some people never learn....

The aim must be to save the company as a whole money, not just one department!!! and especially not to up costs in another department!!!!

With some US companies, reason is not a strong point!!

I would not solder wires directly if you have had pad lifting problems, that means that they are too highly stressed mechanically....

I would use proper screw connectors, properly soldered, in a row, where the soldered joints all work together to withstand a pull on any wire.....

Here are a few examples:-

Just my two cents...I have just recently gone through something similar.

I too am a Engineer by accident and have little to no actual knowledge of standards etc...

But this is what I do.

When soldering wires into a through-hole ALWAYS use solder pads on both sides of the board. Even if your design is single sided. Make it a double and put pads on both sides. Much stronger. And I generally just use a .1 header and change the hole and pad size to match the AWG of the wire.

When using just a pad to solder to. I always try and make the pad as long and skinny has possible so there is as much surface area to solder to as possible. Depending on the location and number of wires (in a row) you can also epoxy the wires to the pcb just below the solder connections. I have also used a hole for a wire tie to help with strain relief. Make the hole like this ---- ( | ) So you can run the tie around the middle section and then around the wires. This works great if you have the room

Or you can do what I just did. I just encapsulated the board in Epoxy...Problem solved!

This is what I have done in the past...Hope it helps.

bill12780

Addressing the lifting of pads: If the board real estate allows, consider adding an extra hole for each wire which is oversized to accept the insulated wire. Thread the wire through the larger hole and then into the hole with the solder pad. The larger hole works as a strain relief. It also assures that the wire will not have solder wicked up into the area that needs to be able to bend.

The problem with connectors with low tech assembly is that they require operators to strip and crimp the wires to exacting standards. They require in process inspections and equipment calibrations as it is often not possible to inspect or test for failures on fully assembled connectors. Was the crimp made with the right tool? Is the crimp free of wire insulation? Etc. Failure to do so introduces failure points.

I agree with Manufacturing Jedi that soldering wires directly to the board may be best. In this situation it could be both the lowest cost and the most reliable solution.

You marked yourself off topic. Why?

I have added a GA to make it slightly better/correct...

You were right on the money for me anyway.......

Back from a short break.

For soldering onto surface pads instead of through hole, the challenges are very different. Management of strain from the cable into the solder joint is your primary concern.

I understand your cost constraints and sometimes even the design constraints will prohibit use of through hole wire system.

suggestion: Make the orientation of the board such that the wire does not "peel" the pads form the substrate. The cable entry should be parallel and directly in line with the solder pads so that the only way they can come off the board is through "shear".

Clarification of previous remark: spacing of 1.5 times sheath diameter is the pitch of the centre lines of the connections. Anything closer than that would present significant challenge to soldering. The difficulty with 0.8mm (between pad) clearances bridging suggest that you have either a larger cable/strand bundle or "poor wetting" of the soldering process. (I am assuming that you have solder resist between the pads.) What is your conductor size and I'll mock something up here to try it out.

The bridging sounds like poor solder tip selection, cold iron, poor flux, contaminated solder pads or whatever else is stoping the solder from wetting into the joint. It could even be that your solder wire is too big in diameter for the task. I would also suggest that you have the wires pre-tinned (solder dipped) to assist in the soldering process.

Remember that the recipe for a good solder joint includes "time" for the materials to properly heat, time for the solder to be added and time for the solder to wet to form the miniscus shape relevant for the materials in use. Bridging can be an outcome of excess solder and insufficient time to allow brides to "snap away". How many wires are involved in this assembly? 30 seconds implies far fewer wires than I understood from your first information.

Hello,

I am designing an SMT component (header with 2 terminals) to be placed on a PCB board with surface pads. The 2 terminal component needs to withstand a 5 lb shock/vibe test in every direction with just the solder joint. I am limiting it to 2 terminals to free up board space. I am trying not to use a threaded insert through the middle of the component for added mechanical retention.

Does anyone know of any existing documentation or calculations for the mating strength of the surface mount terminal with the surface pads after reflow?

I know it will be dependent on the actual solder joint after reflow (lead free), but anything in general will help.

thanks,

Philip

Mechanical Design Engineer

Guest - I recommend that you register and resubmit your comment starting a new thread so that your question will be seen by a larger audience. Very few are currently tracking this old thread.

Not just the solder joint, but also the pad to substrate adheasion strength.

Personally, I wouldn't trust the pads to hold anything more than the component that is being soldered to them, more mechanical securing would be preferable, or mechanical retention of the PCB to a panel including the component to the same panel.

Cutler-Hammer's "design.pdf" can be found on Daan Terstegge's Website: www.smtinfo.net/Db/_DFM.html.
Good luck, Dieter