surface mount-- solder chips first

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surface mount-- solder chips first

Post by honeyb » Thu Jan 30, 2020 4:41 pm

I'm wondering why the standard advice with surface mount soldering is to solder the chips first? Aren't you more likely to damage them by mucking around you do on the board with them installed?

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Re: surface mount-- solder chips first

Post by guest » Thu Jan 30, 2020 4:53 pm

they are more difficult to solder than the resistors, so its easier to do them when there is nothing else on the board.
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Re: surface mount-- solder chips first

Post by honeyb » Thu Jan 30, 2020 4:54 pm

That's what I thought.

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Re: surface mount-- solder chips first

Post by jimfowler » Thu Jan 30, 2020 9:49 pm

In my experience: yes without exception.

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Re: surface mount-- solder chips first

Post by ablearcher » Thu Jan 30, 2020 11:23 pm

Huh, I've always soldered chips last. Especially since I usually douse everything in flux when I do the chips and even after I wash it the board stays sticky.

A couple months ago I started getting stencils, placing everything by hand, then reflowing it all at once on a reflow station/heater, only using the iron for rework. It's been a big upgrade, highly recommended if you spin your own boards.

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Re: surface mount-- solder chips first

Post by sduck » Thu Jan 30, 2020 11:31 pm

^^^ there's always that one person who chimes in and says that they always do the large chips last. I guess that's ok on some boards, and perhaps with better skill sets than I have, but i'm going to stick with doing the big chips first.
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Re: surface mount-- solder chips first

Post by Altitude909 » Thu Jan 30, 2020 11:36 pm

ablearcher wrote:
Thu Jan 30, 2020 11:23 pm
.....getting stencils, placing everything by hand, then reflowing it all at once on a reflow station/heater...

this x1000. Will change your life. Like losing your virginity

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Re: surface mount-- solder chips first

Post by infinitemachinery » Fri Jan 31, 2020 12:19 am

I always solder ICs last also. I find them far easier to solder than single SMD caps or resistors.

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Re: surface mount-- solder chips first

Post by Sikkboy » Fri Jan 31, 2020 12:54 pm

ablearcher wrote:
Thu Jan 30, 2020 11:23 pm
Huh, I've always soldered chips last. Especially since I usually douse everything in flux when I do the chips and even after I wash it the board stays sticky.

A couple months ago I started getting stencils, placing everything by hand, then reflowing it all at once on a reflow station/heater, only using the iron for rework. It's been a big upgrade, highly recommended if you spin your own boards.
How do you get those stencils made? or wheres a good place to order from?

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Re: surface mount-- solder chips first

Post by Altitude909 » Fri Jan 31, 2020 3:29 pm

any place that makes circuit boards will make them. You dont need them framed, it's easy enough to kludge something if you're only doing one board

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Re: surface mount-- solder chips first

Post by Flounderguts » Fri Jan 31, 2020 5:36 pm

My first level up was to start including SMT components.

2nd level up was discovering stencils

3rd level up was hot air work

4th level up was going to hot plate (on sand) or reflow oven

Best level up was going to Loctite solder paste...it's so much better than anything else, I just don't understand how I managed without it.
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Re: surface mount-- solder chips first

Post by Altitude909 » Fri Jan 31, 2020 6:20 pm

Flounderguts wrote:
Fri Jan 31, 2020 5:36 pm
..
Best level up was going to Loctite solder paste...it's so much better than anything else, I just don't understand how I managed without it.
What do you use and what have you used before? I'm kinda meh with the stuff I have now, always looking for something better

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Re: surface mount-- solder chips first

Post by Sikkboy » Fri Jan 31, 2020 7:50 pm

Altitude909 wrote:
Fri Jan 31, 2020 3:29 pm
any place that makes circuit boards will make them. You dont need them framed, it's easy enough to kludge something if you're only doing one board
I do not think there is any here locally where I am currently living, so I have to look through the interwebz for these sorts of resources.

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Re: surface mount-- solder chips first

Post by cloudscapes » Fri Jan 31, 2020 8:21 pm

I don't like having stuff in the way when soldering chips.

If I have to wipe solder away with braid, it's infinitely easier when there aren't a dozen passives lined up millimeters next to the pads.

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Re: surface mount-- solder chips first

Post by Altitude909 » Fri Jan 31, 2020 8:41 pm

Sikkboy wrote:
Fri Jan 31, 2020 7:50 pm
Altitude909 wrote:
Fri Jan 31, 2020 3:29 pm
any place that makes circuit boards will make them. You dont need them framed, it's easy enough to kludge something if you're only doing one board
I do not think there is any here locally where I am currently living, so I have to look through the interwebz for these sorts of resources.
http://www.electronicsandyou.com/blog/t ... china.html

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Re: surface mount-- solder chips first

Post by TheMentat » Fri Jan 31, 2020 9:10 pm

Altitude909 wrote:
Thu Jan 30, 2020 11:36 pm
ablearcher wrote:
Thu Jan 30, 2020 11:23 pm
.....getting stencils, placing everything by hand, then reflowing it all at once on a reflow station/heater...

this x1000. Will change your life. Like losing your virginity
I’ve been thinking about taking the plunge... some of those hackable reflow ovens can be had for pretty cheap.

It would be worth the stencil cost if it reduced errors... I find that I usually have 1 or 2 bad solder joints on a board with hand soldering. Is it much better with reflow ovens?

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Re: surface mount-- solder chips first

Post by Roni » Sat Feb 01, 2020 12:02 am

I do ICs last as well. Really because most of my soldering errors are slightly tombstoned passives and the best magnification that I have is a loupe that needs to be hard up against the board to focus properly. I tend to do all my passives first on hotplate, inspect and test them, then do the ICs and electrolytics last. I find ICs quick and easy to do by hand in tight spaces because I've come to know my tips/heat profile and my technique never requires braid.


.

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Re: surface mount-- solder chips first

Post by latigid on » Sat Feb 01, 2020 3:40 am

I would say it depends on the board. If there's enough clearance I prefer to do the chips last to avoid risks with overheating/static. But on a tight layout you typically work from the inside to the outside and the chips are normally in the middle.

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Re: surface mount-- solder chips first

Post by Altitude909 » Sat Feb 01, 2020 9:17 am

TheMentat wrote:
Fri Jan 31, 2020 9:10 pm
..

I’ve been thinking about taking the plunge... some of those hackable reflow ovens can be had for pretty cheap.

It would be worth the stencil cost if it reduced errors... I find that I usually have 1 or 2 bad solder joints on a board with hand soldering. Is it much better with reflow ovens?
I get the occasional tombstone, that's why I want to go to better paste. I've been using the Chipquick because its cheap and comes in small quantities but I'm starting to get the feel that its cheap for a reason. I switched to this way to deal with the hand solder error rate specifically but really the benefit comes in time, I can place parts by hand and solder the board in the oven in about a third of the time of hand soldering with much better results. There is also an economy of scale when you start doing this, hand soldering 3 boards is pretty close to 3 times the time of soldering 1 board but with paste, placing 3 times the parts is faster and soldering 3x the number of boards doesnt take any longer than soldering one board. Dealing with traditionally difficult to deal with parts (QFN/leadless stuff) is now trivial as well.

>It would be worth the stencil cost

it's 7-10$. Its worth getting just to have available at those prices.

>Is it much better with reflow ovens?
Night and day. It takes about 3 minutes to run the cycle and its done. If you have good no clean paste, the board is ready to use after than. No cleaning needed

>some of those hackable reflow ovens can be had for pretty cheap.

I bought a T-962 after some research. It had mixed reviews but it was $230 shipped on Amazon and there were plenty of tutorials on how to get it up to snuff so I said, fuck it, i can write it off if it sucks. it doesnt suck. I put in maybe another $30 in parts and an hour worth of work making the changes/calibrating it and I use it every day. I can do 4 layer 2oz Cu PSU boards and its no different that 1.6mm 2 layer stuff. You can do 2 sided stuff no problem also, its an IR based oven so the temperature is really focused on the business side of the PCB and the underside stays a good 15 C under that, well below the relow temp (i use 230C @ 10 sec per the solder spec sheet for the max temp)

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Re: surface mount-- solder chips first

Post by guest » Sat Feb 01, 2020 10:51 am

the T962 does need the upgrades to work well (at least in my experience). it works without them, but its not consistent.

as for tombstone, i feel like that has a lot more to do with pad design and trace layout, or thermal gradients in the oven. a good pad for hand soldering is a bad pad for stencil soldering.
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Re: surface mount-- solder chips first

Post by Altitude909 » Sat Feb 01, 2020 12:12 pm

yeah, totally agree with that. I find that parts tombstone on the same pad of the same board.

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Re: surface mount-- solder chips first

Post by TheMentat » Sat Feb 01, 2020 12:15 pm

Altitude909 wrote:
Sat Feb 01, 2020 9:17 am

I get the occasional tombstone...


... solder spec sheet for the max temp)

wow... thanks for the detailed response!

It seems like that loctite stuff doesn't come in hobbyist sized packaging, which is unfortunate for something with such a short shelf-life! Let me know if you find something smaller!

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Re: surface mount-- solder chips first

Post by Sikkboy » Mon Feb 10, 2020 5:04 pm

So I found a place, now what is the best format for the stencils? Stainless steel ? Polymide Film , is it better to have it framed or unframed? whats the best thickness to work with?

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Re: surface mount-- solder chips first

Post by Altitude909 » Mon Feb 10, 2020 7:27 pm

I've only used stainless, standard thickness (.12mm). The frame work is for using it with a stencil printer, I'm not sure if it would be of any benefit without one. I DIYed a rig using unframed stencils that just get taped into place, not great but it works and I'm only doing one or two boards at a time so it's good enough for now

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Re: surface mount-- solder chips first

Post by KSS » Mon Feb 10, 2020 8:59 pm

Altitude909 wrote:
Sat Feb 01, 2020 9:17 am
I can do 4 layer 2oz Cu PSU boards and its no different that 1.6mm 2 layer stuff. You can do 2 sided stuff no problem also, its an IR based oven so the temperature is really focused on the business side of the PCB and the underside stays a good 15 C under that, well below the relow temp
@guest also

What size board or boards? The issue with many lower cost ovens in not that they can't do the job, but that they can't do the job evenly over their entire claimed usable area.

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