solder paste + hot plate, is my paste bad?

[igor78]

I have T3 solder paste (mgchemicals Sn42/Bi57/Ag1) this one https://www.mgchemicals.com/products/soldering-supplies/solder-paste/low-temperature-solder/
If I follow recommended profile with a hot plate I get this results

little balls of solder scattered around.
I etch my PCB myself and I don't have any solder mask.
What is the problem?
Lack of solder mask?
Expired T3 paste?
Not enough heat and/or time on the hot plate?
Something else?

I tried to blow extra with hot air, but it did not seem to help.

[eugene]

I'd try cleaning the pads to remove tarnish and residue before applying the paste. Using something gently abrasive like a green scrub pad might help.

[rob77]

yes , your copper is not clean enough..
polish witch scotch brite + clean with acetone

[igor78]

This is freshly etched copper. Please ignore black marker marks - I was marking component positions, sort of silk-screen.

I did apply liquid tin before the whole soldering process. Are you saying pads should not be tinned before applying the paste?
Or are you saying that black marker marred the pads and I should not have used it?

[eugene]

What I'm thinking is that the solder balls up instead of flowing because the copper is not 'accepting' it. That's typically a problem of too much crud and/or flux that isn't doing its job. OTOH, if the pads are tinned then something else is going on.

Perhaps a little more heat?

I probably should just sit quietly and listen. I've used a converted toaster over for reflow, but never a hotplate. And something like this I would solder by hand anyway. So really I don't have the experience you're looking for.

[Ian.M]

There's a four part blog series you should probably read:
https://www.indium.com/blog/stages-of-a-reflow-profile-part-i.php
https://www.indium.com/blog/stages-of-a-reflow-profile-part-ii.php
https://www.indium.com/blog/stages-of-a-reflow-profile-part-iii.php
https://www.indium.com/blog/stages-of-a-reflow-profile-part-iv.php

It seems likely the spattering could be due to too fast temperature ramp-up causing the solvents in the flux component of the solder to boil.  If so, gently and slowly preheating the board with warm air (staying under 100 °C as rosin based fluxes start melting at around that temperature) to drive off the volatiles before transferring it to the hotplate should help.

I'd be suspicious of tin's tendency to oxidize in a damp environment.  Try scrubbing the bare board with a pink (minimally abrasive)  pan scourer or melamine sponge wetted with IPA, rinsing off with IPA, and drying with paper towel or warm air immediately before starting assembly. 

[Shock]

You can test pastes by using a spare or scrap pcb and taping a thermocouple with kapton to the underside, while monitoring the temp bring it up slowly with hot air to somewhat simulate a profile. Doing the same test with additional flux you can tell if your paste has expired or not been stored correctly etc.

[sleemanj]

How old is the paste, how has it been stored?

[tszaboo]

 I see several posibilities to the issue:
Regular PCBs are not bare Copper, they have a plating which can be Tin, Nickel,  or Gold or other metal. HASL, ENIG and others.
Your paste might be expired.
Your paste doesn't contain enough flux.
Not high enough temperature or time.
Chemical residue on the PCB. Try cleaning it before soldering it next time.

[rob77]

This is freshly etched copper.

yes and it was not clean enough even before etching.. copper must be shiny, if it's not, the you end up with issues. i make my own boards as well , soldering with a looong expired paste and never have issues.

expired solder paste is not a problem for hobby use with hot plate or hot air ( but it would be a big issue for production). you just need to add a bit more than usual and visually check when it flows.. you can't rely on the original temperature profile with expired paste.

if your paste is dried out, then add a little bit of flux + a bit of IPA, stir it up, work it with a spatula for a while till it has the "good" consistency and it's good as new for hobby use

[Bud]

I've seen old solder paste balling like this. I also agree with Ian.M that improper reflow temperature profile may also cause it.

[cdev]

What paste has the best shelf life in the refrigerator. So manytimes Ive bought some and then had it just get too old and then its got this sputtering problem, is there any way to preserve its freshness?

[mon2]

Try LOCTITE GC-10 - excellent paste and can be stored at room temp. We have been using this for the past 2 year on our SMT line and love the results. Used to solder down WLCSP packages (1.4*1.4mm = Lattice ICE40UL1K). Give it a try.

[cdev]

Thank you. I will write this down and try it. How long is it okay for? (Refrigerated)

[free_electron]

your ramptime is too long. what is happening is the flux is boiling off completely before you hit the melting point. you are essentially soldering "dry". the3 solder does not flow because your flux is completely gone.

[Kean]

Thank you. I will write this down and try it. How long is it okay for? (Refrigerated)

GC10 paste should not be refrigerated, just keep it at room temperature and away from sunlight etc.  It has a 1 year shelf life, but you sometimes get it part way through that depending on the turn over of the seller you buy from.

It is also sold in 500g jars as the smallest size, but if you search the forums here about GC10 you can find some equivalent ChipQuik product in smaller amounts available from DK.  I buy the 500g jars but usually only get about half way through them before expiry.  I continue to use the paste for a few more months after expiry if it is still giving good results.

[KevWal]

Hi

Could somone suggest some GC10 alternatives please  - Chip Quik or others?

Thanks very much
Kevin

[mon2]

Why an alternative to GC10 ? Are you having difficulty sourcing in your market ? Otherwise, GC10 is hard to beat - we use it in production for all of our builds and absolutely love the stuff.

Reach out to the vendor where we source the GC10 paste for advice:

Dave McAuley
Adtool Corp.
514-943-4857
WWW.ADTOOL.CA
Dave McAuley <dmcauley[at]adtool.ca>

514-482-2548
800-361-6727

[KevWal]

Why alternative? Because I can't justify £150 for a tub when I reflow absolute maximum of 1 small board a week

Cheers
Kev

[Kean]

Hi

Could somone suggest some GC10 alternatives please  - Chip Quik or others?

Thanks very much
Kevin

https://www.eevblog.com/forum/manufacture/leaded-equivalent-to-gc10/msg2565963/#msg2565963

[mon2]

Because I can't justify £150 for a tub

Like every vendor of solder paste, they sell in different sizes.

[sleemanj]

Like every vendor of solder paste, they sell in different sizes.

sold in 500g jars as the smallest size

[TassiloH]

How long is it okay for? (Refrigerated)

GC10 paste should not be refrigerated

To add some real-life experience: I bought a jar of GC10 in April of 2018. It is stored in the fridge (around 6°C) in a sealed plastic bag. Every now and then (i.e. couple of months), I remove it from the fridge, let it warm to room temperature (to make it soft and prevent water condensing in the jar), and fill a syringe with the paste. The jar goes back into the fridge, and I use the contents of the syringe (stored in the basement at an average temp of maybe 15°C) for the next couple of months.

I think the paste still performs as good as in 2018 (printed with stainless steel stencil, soldering in reflow oven). There is a minimal amount of solvent separation visible in the jar, so maybe it will be necessary to mix it up thoroughly before filling the syringe next time.

[E-Design]

How long is it okay for? (Refrigerated)

GC10 paste should not be refrigerated

To add some real-life experience: I bought a jar of GC10 in April of 2018. It is stored in the fridge (around 6°C) in a sealed plastic bag. Every now and then (i.e. couple of months), I remove it from the fridge, let it warm to room temperature (to make it soft and prevent water condensing in the jar), and fill a syringe with the paste. The jar goes back into the fridge, and I use the contents of the syringe (stored in the basement at an average temp of maybe 15°C) for the next couple of months.

I think the paste still performs as good as in 2018 (printed with stainless steel stencil, soldering in reflow oven). There is a minimal amount of solvent separation visible in the jar, so maybe it will be necessary to mix it up thoroughly before filling the syringe next time.

Agreed. I'd like to hear what the reasoning is for not storing sealed GC-10 in refrigeration (well above freezing). I also store it that way and have had zero issues with it.

[Kean]

Agreed. I'd like to hear what the reasoning is for not storing sealed GC-10 in refrigeration (well above freezing). I also store it that way and have had zero issues with it.

Good question.  I thought I had seen something in the technical data sheet, but I cannot locate anything specific now.   
In the TDS the optimal storage temperature range is 5 to 25°C (+/-1.5°C), and most fridges should sit at around 2 to 3°C.
ISTR something about crystallization of the flux, and being difficult to remix.  Maybe a sales rep mentioned it.