<rqou>
i just realized i never assembled my t962 thermocouple upgrade
<rqou>
which means i now need to go find it lol
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<rqou>
wheee i _finally_ found my board
<rqou>
after an hour+ of searching
<rqou>
azonenberg: ping?
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<azonenberg>
rqou: back
<rqou>
azonenberg: two questions
<rqou>
1) do you have a system for tracking where all your lab shit is? :P
<rqou>
2) what is your standard reflow profile?
<azonenberg>
1) no, i have standard places for where tools go and when they're not there i get mad :p
<rqou>
lolol
<azonenberg>
Because it means somebody touched it, or i didn't put it away
<azonenberg>
Usually the latter (got interrupted while working)
<azonenberg>
2) Place board on cookie sheet, set convection toaster oven to "cookies" mode / 425F
<azonenberg>
turn on, wait until solder melts
<rqou>
right, you still use that hack profile
<azonenberg>
wait another 15 sec, turn off oven, wait 15 sec, open door
<azonenberg>
i havent measured the actual temperatures but it gives very good performance m
<azonenberg>
my only complaint is the peak temp is about 10-15F lower than i'd like
<rqou>
actually, another question: i have some unrefrigerated solder paste from a year+ ago that i never got around to using, is it still any good or should i chuck it?
<rqou>
azonenberg: also: if i am uncertain about the performance of my reflow oven, what is the "safer" direction to adjust the profile?
<azonenberg>
rqou: i dont fridge my paste, i find evaporation of solvents is mostly what kills it
<azonenberg>
higher temps lead to a tiny bit of oxidation on the solder balls but i've never had yield issues from that
<azonenberg>
If it doesn't print right, i chuck it though
<rqou>
oh i'm not going to use it on my actual board
<azonenberg>
i tend to replace paste about every year due to solvent loss issues
<rqou>
i was going to just try it on the thermocouple mod board for my T962
<rqou>
which doesn't have a stencil anyways
<azonenberg>
it starts to get too thick and dry and acts more like that sculpy sand stuff than paste
<rqou>
yeah it definitely looks like that already
<azonenberg>
Then i'd toss it, but i'd say that's from old age and not lack of refrigeration
<azonenberg>
syringes last longer than jars b/c lower exposed surface area but you do still get diffusion through the plunger etc
<azonenberg>
they're not airtight
<rqou>
this is a jar so probably even worse
<rqou>
> also: if i am uncertain about the performance of my reflow oven, what is the "safer" direction to adjust the profile?
<azonenberg>
Regarding performance, i dont have any empirical data on my oven's actual temp or anything
<azonenberg>
Basically what you're shooting to do is hit the melting point of SAC305 (219C) then at least another 5-10 deg to get good flowing
<azonenberg>
but not tooooo much beyond that
<rqou>
and if you leave it too long?
<azonenberg>
i think i hit like 225-230C on my oven and 240-260 is closer to optimal process window
<azonenberg>
You risk compromising long-term reliability and maybe messing with trim on sensitive analog
<azonenberg>
but a short overcook probably wont outright kill the chip
<azonenberg>
i have never had a part fail from a proper reflow
<azonenberg>
the only time i've killed parts with heat is with excessive hot airing
<azonenberg>
and we're talking things like insulation on an inductor burning off
<azonenberg>
or plastic connectors melting
<azonenberg>
not semiconductor failure
<rqou>
so if i'm not sure, can i adjust the reflow time towards the longer side and slightly higher temps?
<rqou>
i'll probably make the preheat time longer too
<rqou>
wait wait wait
<rqou>
azonenberg: you don't use a trapezoid profile at all?
<azonenberg>
I rely on the thermal inertia of the oven to get me close enough
<azonenberg>
but its roughly a linar ramp
<azonenberg>
linear*
<azonenberg>
i used to use a trapezoidal profile on my old IR oven with no convectoin
<azonenberg>
this one heats evenly and not too aggressively, it usually takes somewhere around 6-8 minutes to do a full reflow cyclew
<azonenberg>
and the whole board melts within a few seconds
<azonenberg>
so very uniform temps
<rqou>
hmm so most of your issues are with connectors and other "weird" parts?
<azonenberg>
I have never, i repeat never, had a part designed to survive reflow fail in this oven
<azonenberg>
only during rework or hand soldering
<rqou>
ah
<azonenberg>
And with my old single element IR toaster oven that was so non-uniform sometimes the middle of the board would scorch before the edges melted
<rqou>
how do you do double-sided load?
<azonenberg>
I pick the side with the lower number of high-mass components/connectors, typically designated the bottom in cad
<azonenberg>
paste, place, reflow
<azonenberg>
let cool fully to room temp
<azonenberg>
Flip over, paste top side (still working on a good jig to do this)
<azonenberg>
place, reflow
<azonenberg>
Let cool a bit, then hand solder PTH
<rqou>
do you have a jig to hold the board up?
<azonenberg>
I build one to suit out of scrap pcb and masking tape
<azonenberg>
talking to a locla machine shop about making a proper jig
<azonenberg>
local*
<azonenberg>
nobody seems to make such a product
<azonenberg>
you can get printers for full framed stencils easily
<azonenberg>
but nobody has a good adjustable jig for using frameless stencils on a 2-side-placement board
<azonenberg>
anyway, in the very rare situation that i have a high density part on the underside
<azonenberg>
i'll either epoxy it down or hand solder / hot air after the reflow is done
<azonenberg>
i've epoxied a few big connectors
<azonenberg>
but you'd be surprised at how well parts stay on especially with lead-free solder which has slightly stronger surface tension
<azonenberg>
There's an equation you can find if you google around to calculate how heavy a part can be unsupported on a bottom side of a board
<azonenberg>
based on the surface tension coefficient of your solder alloy, mass of the part, and i believe the sum of perimeters of the smt pads
<azonenberg>
then multiply by some safety margin
<rqou>
yeah well i'm usually not brave enough to put huge parts on both sides
<azonenberg>
Rough rule of thumb, SMT electrolytic caps are a no-go
<azonenberg>
pretty much all chip components are fine
<rqou>
e.g. right now the bottom only has ceramic caps
<azonenberg>
small qfn/sot/sop are fine
<azonenberg>
i'd be leery of a >100 pin qfp
<rqou>
what about a giant 1000+ ball bga on the bottom?
<azonenberg>
too heavy and not enough pad area
<azonenberg>
honestly, i'd declare that the top of the board and worry about what was on the other side instead :p
<rqou>
what if you have one of those on both sides :P :P :P
<azonenberg>
Since i probably dont have 1000+ ball bgas on both sides
<azonenberg>
For thermal reasons
<azonenberg>
you need heatsinks on parts that large, typically
<azonenberg>
And its easier to have one side of the board be the heatsink side
<azonenberg>
also, routability
<rqou>
but more seriously, something like ddr rams in "clamshell" wiring would be fine?
<azonenberg>
it's an improbable enough scenario i've never spent any time thinking about how to deal with it
<azonenberg>
Yes, ddr bgas should be fine without any underfill or epoxy
<azonenberg>
it's mostly large SMT connectors that i'd be concerned about or glue
<azonenberg>
like a smt magjack
<azonenberg>
If i had to put that on the bottom i'd glue it
<rqou>
i usually don't run those connectors through reflow anyways
<azonenberg>
after the first reflow profile, so it self-aligns
<azonenberg>
You can get them SMT designed for reflow
<azonenberg>
normal ones arent
<azonenberg>
My point is, if you use reasonable DFM practices when designing the board
<azonenberg>
2-side reflow is largely a non-issue
<azonenberg>
its just a second pass doing exactly what you did the first time
<azonenberg>
the only challenge is pasting it, like i said i'm still working out a good jig
<rqou>
yeah i don't have a good setup either
<rqou>
i should get my laser cutter working again and make a jig
<awygle>
current/slew rate limiting slash series termination calculations for Glasgow
<awygle>
I'm a bit unsure because it's bidirectional and also weird
<awygle>
Gonna spice it tomorrow but would appreciate your thoughts
<azonenberg>
I can't help but laugh
<azonenberg>
every... single... one
<awygle>
Yeah yeah you went through this already :-P
<azonenberg>
you guys are hitting every design decision i made in starshipraider
<azonenberg>
and every problem
<awygle>
Well of course we are
<awygle>
Same rough problem same rough design space
<awygle>
We just have a different cost function to optimize
<azonenberg>
it's very much validating to my engineering though
<rqou>
nobody seems to like my approach of "have simple buffers and hope that only those get blown up"
<azonenberg>
in that so far, you havent found any grossly superior alternatives
<awygle>
rqou: I wanted to run straight off the fpga lol
<rqou>
i'm not quite _that_ brave
<awygle>
but people need 5v apparently *shrug*
<azonenberg>
total trace cap is pF? or pF/cm
<awygle>
it's pF
<rqou>
i still need to find time to work on my project Guren :P
<azonenberg>
your target is 50 MHz?
<awygle>
yeah that's the max on the level shifter for Rev B
<azonenberg>
keep in mind, two cascaded filters with -3 dB cutoff
<azonenberg>
will be more like -6 dB at 50 MHz
<azonenberg>
(and 50 MHz != 50 Mbps)
<awygle>
they're not cascaded though, it redrives
<azonenberg>
oh, ok
<awygle>
and it's 100Mbps/50MHz
<azonenberg>
still -3 dB is half your amplitude gone
<awygle>
true, should probably up that
<awygle>
too used to 3dB not matter ing
<awygle>
5x you think? 250MHz
<azonenberg>
this isnt rf :p lol
<azonenberg>
i'd look at what typical Vih/Vil of target devices are
<azonenberg>
then calculate how many dB you can tolerate
<azonenberg>
figure out the max freq you care about for nice rise times and a decent eye opening
<rqou>
azonenberg: btw, do you clean boards before pasting them?
<azonenberg>
i'm doing theoretical work to roughly estimate but then actually plotting PRBS's to validate
<awygle>
yeah ok
<awygle>
more math :-(
<azonenberg>
rqou: yes and no
<rqou>
awygle: hey, that's what your fancy piece of paper qualifies you for :P :P :P
<azonenberg>
If fresh from the fab i am not too worried about contamination
<azonenberg>
however, when i sand off the mouse bites i get fiberglass dust all over the board
<rqou>
nah this board has been sitting around for like 2 years (the t962 mod board)
<azonenberg>
So i use a lint-free wipe with some IPA to remove it
<awygle>
I hate those goddamn mouse bites
<azonenberg>
and i often give the face of the pcb a little wipe
<azonenberg>
but its for dust removal, not surface cleaning
<awygle>
Either they look like shit or they make me all itchy
<azonenberg>
if it had been sitting around for a while i'd do a more extensive IPA scrub
<awygle>
We should never have invented fiberglass
<rqou>
awygle: yeah, just use asbestos instead :P
<azonenberg>
awygle: hey, if you want more fiberglass
<azonenberg>
come over my house
<rqou>
gotta pay the mesothelioma lawyers somehow :P :P :P
<azonenberg>
we have cubic yards of it that need to go up this weekend
<azonenberg>
hoping to get insulation inspected mon-tues :p
<rqou>
O_o that fast?
<rqou>
oh wait, insulation
<rqou>
not sheetrock
<awygle>
I deeply do not want more fiberglass
<azonenberg>
lol
<azonenberg>
rqou: we finished another room today
<awygle>
Anyway thanks for the notes azonenberg
<azonenberg>
sheetrock arrives monday
<awygle>
I'm going to bed
<azonenberg>
awygle: but yeah i would definitely spice it
<rqou>
also, how the fuck is mesothelioma so SEO-ed?
<azonenberg>
then build a prototype and validate
<awygle>
I think we can solve this problem with a 39 Ohm resistor and bigger caps
<azonenberg>
rqou: because one suit can win you $$$$M
<awygle>
But we'll find out tomorrow and then again much later
<azonenberg>
its literally the most seo'd query
<azonenberg>
a single link click costs the advertiser like 50 USD or something
<rqou>
is it?
<rqou>
<foo>.dll is also pretty full of SEO spam
<azonenberg>
Last time i saw stats yet
<azonenberg>
yes*
<azonenberg>
that is up there but not to the point of extreme adwords spedning
<rqou>
also, is it just me or is the "<foo>.dll" SEO spam getting worse and worse?
<rqou>
(also, i also work for a company that does search now so glass houses and all that)
<azonenberg>
havent looked in a while since i dont use windows
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<whitequark>
rqou: uh, i have an extensive home lab
<rqou>
whitequark: ok, how do you organize it?
<whitequark>
rqou: which parts
<whitequark>
for chemistry i have two ikea cabinets, one has reagents in bottles sorted by type on each shelf
<rqou>
any of it? right now i have a giant clusterfuck of plastic bins from when i moved out of berkeley
<whitequark>
i.e. salts/dry organics on top shelf, then solvents, then acids/bases, then empty bottles
<whitequark>
or rather acids/bases are temporarily in a different cabinet until i add proper spill protection
<whitequark>
the other cabinet has glassware just lying on shelves
<whitequark>
ideally there would be heavy foam with cutouts, but i couldnt find any that wasnt for a ridiculous price
<whitequark>
so, the glassware is there sorted. uhhh
<rqou>
no acid-proof/flame-proof/explosion-proof cabinets?
<whitequark>
top shelf: pipettes, then distillation heads and condensers, then assorted flasks, then funnels and such, then stirring rods, on the bottom shelf i store the heavieststuff
<whitequark>
like magstirrers and dessicators
<whitequark>
flame-proof/explosion-proof: i dont store any solvents volatile enough to warrant that, like diethyl ether
<whitequark>
if i do it will probably just be outside
<whitequark>
this apartment is generally way too flammable for comfort
<whitequark>
acid-proof: just get $1 PP boxes
<whitequark>
PP is resistant to pretty much all common acids incl conc sulfuric
<whitequark>
and even piranha
<whitequark>
i don't think it'll survive rfna
<whitequark>
but generally, common PE/PP storage ware you get from home despot or whatever is well acid proof enough to equip a real lab with it that doesn't have budgets you get from working on the stuff that's in fashion
<whitequark>
like how do you think highschool or just underfunded labs get equipped in ru? people go to fucking ikea
<rqou>
lol really?
<whitequark>
for a chem table, take a PP or HDPE sheet and fix it to a regular ikea table with uhhh
<whitequark>
yes
<whitequark>
obviously duh
<whitequark>
if we're talking about biology, i'm -pretty- sure some people use pressure cookers instead of autoclaves
<rqou>
my high school worked by having some competent teachers go poking around local biotech companies to salvage stuff they're throwing away
<whitequark>
so, here's two general schools of thought
<whitequark>
first, you can get surplus/discarded equipment and teach your students on the real deal
<whitequark>
the US has the best surplus equipment market in the world so it makes a whole lot of sense to make good use of it
<whitequark>
second, you can get by with whatever's in your local hardware store, and teach your students how shit works in the real world
<whitequark>
you'll be surprised how much of biotech is just slapping shit together
<whitequark>
sure, there's stuff like flow cells and nanopore sequencers, but for each of those there's a hundred undergrads on a shoestring budget
<rqou>
well, my high school was silicon-valley-adjacent so there was definitely fancy stuff floating around
<rqou>
not for the actual IT infrastructure though
<whitequark>
awygle: re USB C: sure, let's have USB C in compat mode
<whitequark>
it doesn't need a board cutout, less headache
<whitequark>
and we should use a PTH one I think
<whitequark>
though I'm not sure
<rqou>
whitequark: hmm now i'm curious: what is/was the state of IT in RU high schools?
<rqou>
e.g. my school was running win95 on some machines up until ~2011-2012
<whitequark>
wtf
<whitequark>
no we had xp in 2007-2009
<rqou>
most machines were xp
<whitequark>
and there was a linux experiment going on
<whitequark>
state-sponsored actually
<rqou>
just some win95 lingered around
<whitequark>
not sure if it ever grew into something useful
<rqou>
when they got replaced it was because we got a new principal who also said "wtf"
<rqou>
plus there was some economic stimulus whatever going around
<rqou>
so everything that was a piece of junk got upgraded to win7
<rqou>
whitequark: how common are really dumb contracts with kickbacks in RU?
<rqou>
or is corruption more overt there? :P
<whitequark>
rqou: kickbacks are extremely common
<whitequark>
corruption takes all forms.
<whitequark>
if patrol cops catch you with drugs, they openly say that either you pay them (say) 100k rub, or they plant more drugs on you, enough for a prison term
<whitequark>
amusingly, the price varies depending on how much they think you'll pay. if they're in good mood, some poor student might get away with 10k
<whitequark>
you also get a ride to the nearest atm in the patrol car, you know, convenience and all
<whitequark>
awygle: so I don't get where you got 160 ohm resistors
<rqou>
whelp, this was a total disaster
<rqou>
solder paste got nowhere near melting
<rqou>
reworking a failed reflow is really difficult
<whitequark>
really?
<whitequark>
i threw out my old shitty hot air gun and now it's a breeze
<whitequark>
i can desolder FPCs every single time without so much as making them slightly brown, and that's with lead-free
<whitequark>
FPC connectors
<whitequark>
well, I can desolder FPCs too, but not with a heat gun
<whitequark>
honestly I've yet to find a circuit I couldn't rework when needed lol
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<cr1901_modern>
whitequark: What heat gun do you use? I assume you have a nozzle for it as well?
<whitequark>
cr1901_modern: no nozzle
<whitequark>
just whatever it goes with
<whitequark>
it's a local brand, some chinese made gun relabeled i think
<whitequark>
not sure which
<cr1901_modern>
I would've figured that not having a nozzle would be too imprecise and you'd blast nearby components w/ too much heat accidentally
<cr1901_modern>
I guess the air between the gun and components is enough to prevent this
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<awygle>
whitequark: that's because 160 was before azonenberg reminded me this isn't rf
<awygle>
classic non functional comments problem
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<rqou>
whelp, i think i plugged something in wrong and blew out the power stage of the reflow oven
<rqou>
goddammit
<rqou>
FML
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<eduardo>
bubble_buster: as a university you very likely get a free license of the SymbiticEDA suite which includes SV support (once the license manager is done :-) Just get in contact with clifford@symbioticeda.com
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<pie_>
azonenberg you need to make an intel socket compatible riscv processor for replacing intel chips in old thinkpads
<pie_>
take us into the light
<zkms>
more useful would be to make a replacement for PCH since that's where Intel Management Engine lives
<pie_>
yeah i wasnt really going for feasible x)
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<eduardo>
yrozap:
<eduardo>
cyrozap: your webpage is dead. Your Twitter account is inactive. I am working with @oe1cxw and others on OSS FPGA tools. www.symbioticeda.com is the commercail framework for it.
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<kc8apf>
rqou: I use a few different systems depending on what I'm storing.
<kc8apf>
idk. I consider the Allit boxes a bargain compared to Sortimo
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<kc8apf>
still looking for a better solution than ziplock bags in a cardboard box for vacuum tubes
<awygle>
the leevalley and aidetek here seem, subjectively, to be good prices for what they are. the allits seem pricey relative to complexity. but i know ~nothing about boxes or plastic or manufacturing.
<awygle>
at some point i really have to get over my extremely incorrect ideas of how much things cost
<kc8apf>
Lee Valley is just reselling Allit
<kc8apf>
the small Allits were $9 a few weeks ago
<kc8apf>
I need to find a distributor who deals in bulk sales
<rqou>
goddammit today i poked around at the reflow oven and it's working again
<rqou>
FML again
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<rqou>
anyways, reflow oven mod finally seems to work correctly
<rqou>
now i can actually get back to tuning reflow profiles
<rqou>
also, the MAX31850 is a really really cool chip
<awygle>
i feel like i had a problem with that chip and grounding, but i can't remember the details
<rqou>
wait how?
<rqou>
it only has a single ground pin
<rqou>
also, why were you using this chip?
<awygle>
idk, i maybe ended up with a ground loop because the tc was contacting the oven
<rqou>
ah maybe
<rqou>
i did seem to have an issue with bad readings if you don't clean enough flux off
<rqou>
but that's probably typical for sensitive analog
<awygle>
the tc i had was the "drill a hole and screw it in" type and one side was shorted to the screwing part
<awygle>
iirc
<rqou>
also i love how the adafruit breakout for this part is $15 for one sensor
<rqou>
i guess it might be good if you don't enjoy spending hours reworking a failed reflow
<rqou>
adafruit pricing is always really screwy to me
<rqou>
some stuff like breakouts are crazy expensive
<rqou>
some parts like pin headers are actually cheaper than many other vendors for the quality that you get
<rqou>
do i need more time above liquidus or is this ok?
<awygle>
I'm a leaded guy except very recently
<rqou>
fine, what's your opinion as a mostly-leaded-solder user? :P
<rqou>
also, no rohs for you?
<rqou>
hmm apparently crappy-looking joints like this are "normal" for lead-free
<rqou>
i'm probably going to tweak time above liquidus to be slightly higher though
<cyrozap>
eduardo: Thanks for the heads-up. Looks like the server was completely locked up for the past few weeks--maybe I should get some monitoring on that :P
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<cpresser>
rqou: how old was this paste? was it well mixed?
<cpresser>
it seems like the flux did not properly activate
<rqou>
brand new, but just haphazardly syringed onto a scrap board
<cpresser>
ir-reflow?
<rqou>
yes
<rqou>
the scrap board is also several years old and wasn't cleaned
<awygle>
Yeah I'd bump the temp a bit maybe. And clean the board first.
<cpresser>
its hard to tell what exactly went wrong.
<awygle>
I'm trying to transition to rohs but space hates rohs so it's recent for me
<rqou>
i mean, i did see everything liquify
<rqou>
it just looks like a cold joint, but I'm used to leaded
<cpresser>
imho its a flux issue
<awygle>
Possibly very stupid question - does it make sense to anybody to write a *C* wrapper for a *python* library?
<cpresser>
the pads should be fully covered if the flux works as intended.
<cpresser>
the big pad left of the D1 text shows this very clearly
<cpresser>
got a link to the paste you used?
<rqou>
ok, i ran the same board through a second cycle with more flux and it looks better
<rqou>
cpresser: it's kester nxg1 as repacked by oshstencils
<rqou>
still doesn't fully cover the pad though
<cpresser>
how did you add flux? isnt the flux in the paste?
<rqou>
the paste does have flux
<cpresser>
yep, just checked the datasheet
<cpresser>
usually the soak- or dwell-zone in the profile is intended to activate the flux. perhaps yours was to short?
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<rqou>
alright, i ran an adjusted profile and the texture of the solder looks fine now but pads still aren't fully covered
<rqou>
time above liquidus is a bit on the long side at ~90 seconds
<rqou>
I'll try adjusting soak to be longer
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<rqou>
cpresser: ok, longer soak seems to be better
<rqou>
residual issues seem to just be a result of haphazard syringing and the fact that lead-free just doesn't wet the pads as eagerly as leaded
<rqou>
also combined with "this board is really really old"
<rqou>
probably good to go for the real board with an actual stencil
<rqou>
yeah, the test board was really difficult to solder on even by hand so it's probably just oxidized