Prototype oven recommendations

Hi Wouter,

On 9/5/2014 2:54 PM, Wouter van Ooijen wrote:
>>> Same here. The largest PCB I put in it was a eurocard (100x160mm).
>>
>> Surely not a *single* board? Or, is that just all you needed to
>> bake at that time?
>
> No, the total series was IIRC 60, but each board needed some afterwork,
> troug-hole soldering, and then testing, so why not put them in one at a
> time while I was doing the other work. The middle area of the oven
> seemed to work more reliable.

Ah!  Different work process than me.  I would, instead, have stacked
the reflowed boards and did the secondary processing a day, week, etc.
later.  So that I am only focused on one activity at a time (less
chance of forgetting some little detail -- especially on boards that
are "made once", not repeatedly).

[The last cheesecake I made I realized I had failed to mix the
*sugar* (gack!) into the filling -- because I was trying to prepare
dinner at the same time!  :<  Thankfully, caught it 10 seconds
after placing it in the oven so I was able to remove the filling,
mix in the sugar, reassemble and restart the process!  <:-( ]

By "middle", is this consistent with Joe's "avoid the inch around the
periphery" comment?  Or, are you claiming an even smaller "sweet spot"?

>>> I totally agree.
>>
>> I think if you are a business involved in manufacturing boards,
>> you use a different set of criteria.
>
> I do produce boards, but in very limited quatity (10's/year rather than
> 100's)

I'll build a few hundred, total, (though different designs) and scrap
the oven afterwards.  Nor will they all be built at the same time.
E.g., build one/couple of each design, as required (to characterize
them as well as debug the software, etc.).  Then, once satisfied,
buy the balance of the components and fab the remainder.  If a
design change necessitates scrapping some *bare* PCB's... <shrug>...
much preferred to scrapping a bunch of fabbed boards that "won't work"
along with all the components thereon!

In article <lud7po$p59$1@speranza.aioe.org>, this@is.not.me.com says...
> 
> Hi Joe,
> On 9/5/2014 1:04 PM, Joe Chisolm wrote:
....

> > I have a small air powered
> > paste dispenser with a foot pedal.  For dense and or large boards that
> > gets old quick.  I'm more than happy to spend the $100 or so for a
> > stencil. Your time can go from 30 minutes squirting pads to 3 or 4
> > minutes.  Sometimes it takes longer to clean up the stencil than
> > to actually paste the boards.

Yes cleaning stencil can be time consumiong.

I have not paid $100 for a stencil or even a stencil pair, I think the
MOST I have paid was about $75 for a pair of stencils 250 micron 
stainless steel for both sides of a board 350 x 250mm.

Often PCB houses I deal with do free stencils with prototype qty boards
so no brainer on getting stencil even if it is 400 micron not so good 
for below 0.5mm pitch.

My largest quantity I have used stencils or even small toaster oven kit
from Beta layout is 12, normal quantity is 2 (never do 1 always have a 
spare). That oven does 290 x 290 mm approx boards. Not wonderful but 
does the job had to replace elements (about $20 including shipping).
The kit cost about $300 at the time and has more than paid for itself.

Looked at T-962 series an would only consider the ones on Ebay that
have been OEMed to have different controller in for better control
and profiles. Small outfit in UK who retrofit them or sell kit to modify
them.

.... 
> I don't want to build boards for a living.  That's a *job*!  :>
> 
> Likewise, I'm not fond of doing layouts.  But, it's a lot easier
> than having to hover over another engineer's shoulder advising him
> of mechanical interference issues.  Or, having to abandon a
> particular approach because "things don't fit" -- instead of being
> able to make a design change on-the-fly.

Well I do the layout and doing prototype build run on small boards in 
small oven saves time and hassle of getting kits for a fab shop or
paying their costs for proto assembly. That way I know the right parts
are used. Especially as often I am dealing with samples of chips not
available in less than tray quantities. Dont get me on the huge box
to air freioght 6 samples from Taiwan the chip was QFN 6mm x 6mm, the
freighting box was about 750mm x 300mm x 250mm.
 
> Rather, I will build boards (and do layouts) of necessity to be
> more agile in my design/fab process.  Once "done", dispose of all
> the associated kit -- having extracted all the necessary value
> from it.

In some cases I have done one off systems including spares then got 
repeat orders because production was ramped up, so having known stencils
helped.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.pcserviceselectronics.co.uk/pi/>  Raspberry Pi Add-ons
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.badweb.org.uk/> For those web sites you hate

On 9/5/2014 5:00 PM, Don Y wrote:
> Hi Wouter,
>
> On 9/5/2014 11:34 AM, Wouter van Ooijen wrote:
>>> I have a T-962A that I've used for several years.
>>
>> After using a toaster oven with home-brew temperature control I bought a
>> T-962. For the price I am very statisfied with it.
>
> I just can't see using a toaster oven.  It reeks of amateurism.
> (like buying a $99 workstation!  "How committed to this endeavor
> *are* you, really??"  :> )

So I guess you would never use a dishwasher to clean the boards?  That 
has to seem very amateurish too, no?  Ask JL.


> I'm somewhere in the middle.  I don't want to save pennies at the
> expense of hours (or *scrap*!).

Can you define "pennies"?


> OTOH, I don't want to be tied to
> a piece of kit that I then need to "feed, regularly" to justify
> the expense!  Nor do I want to discover 6 mos or a year down the road
> that the fab was "marginal" and I've now got bits of kit failing
> that need AVOIDABLE rework.  Or, that the *design* had a flaw that
> manifested after a lengthy usage period and now I have to refab
> those affected boards.

How are you going to select an oven based on this criterion, "avoidable 
rework"?  Do ovens come with an "avoidable rework" index?

Everything you buy will have risk.  Spend too little (or more than 
enough, but on the wrong unit) and you have problems.  Spend too much 
and you just spend too much with little improvement in utility.

-- 

Rick

Hi Paul,

On 9/5/2014 3:41 PM, Paul wrote:

>> I don't want to build boards for a living.  That's a *job*!  :>
>>
>> Likewise, I'm not fond of doing layouts.  But, it's a lot easier
>> than having to hover over another engineer's shoulder advising him
>> of mechanical interference issues.  Or, having to abandon a
>> particular approach because "things don't fit" -- instead of being
>> able to make a design change on-the-fly.
>
> Well I do the layout and doing prototype build run on small boards in
> small oven saves time and hassle of getting kits for a fab shop or
> paying their costs for proto assembly. That way I know the right parts
> are used. Especially as often I am dealing with samples of chips not
> available in less than tray quantities. Dont get me on the huge box
> to air freioght 6 samples from Taiwan the chip was QFN 6mm x 6mm, the
> freighting box was about 750mm x 300mm x 250mm.

It's not just a cost issue.  You get to see if the artwork, silkscreen,
mask, etc. *really* give you a manufacturable board (especially if
you also want hobbyists to be able to fab them -- at their own risk).
You might not realize (in layout) that the placement of a silkscreen
legend makes it ambiguous whether component X or Y fits into a
particular location.  Or, that there is some mechanical interference
that you didn't foresee.

Yeah, a fab house *can* spot these things.  And, hopefully, convey
ALL of them to you.  Or not.  If it's a local shop, perhaps you can
drop in on them when you're in that part of town, etc.

IME (building prototypes for clients), it was *so* much easier to just
build the first unit myself and see, first-hand, what the potential
problems were likely to be.  Of course, a different set of eyes, hands
and tools might turn up *other* problems (I've had problems with
pick-and-place in the past... hard for me to verify on my own  :< )

>> Rather, I will build boards (and do layouts) of necessity to be
>> more agile in my design/fab process.  Once "done", dispose of all
>> the associated kit -- having extracted all the necessary value
>> from it.
>
> In some cases I have done one off systems including spares then got
> repeat orders because production was ramped up, so having known stencils
> helped.

I will be building some number of "first samples" -- true prototypes
to actually verify the functionality of the design, software, etc.
Easier to prototype in foil -- especially with the devices that I
am using and some of the packaging constraints.

If any of the designs/layouts prove to be faulty, I can scrap the
remaining boards (of that particular design); turn the crank, again;
and repeat with the newly revised design/layout.

Once everything are proven "acceptable" (no rework or just minor
rework required... some of which may be easier to do on *bare*
boards), I will proceed to make the rest of the prototype *run*
for the prototype *system* (quantity one).

[Though this will tend to be a staggered effort as the entire system
won't be done at a single point in time with *just* the "first
samples".  Instead, I may finish producing *all* of the "design #6"
boards before I build the *second* "design #2" board.  E.g., the
highest quantity design will be fabbed in many stages as I won't
need *all* of them until the very last moment.]

I.e., I *know* how many of each design/layout I will eventually
be building -- *I* am the customer!  If I find someone who wants
to produce more (for themselves or for sale), then I could hand
off to them any tools I have acquired/created in the process.

Or, not.  (e.g., they might want to make changes to the design
going forward)

On Fri, 05 Sep 2014 13:52:12 -0700, Don Y wrote:

> Hi Joe,
> 
> On 9/5/2014 1:04 PM, Joe Chisolm wrote:
> 
> [elided]
> 
>>>> I have a T-962A that I've used for several years.  Probably put 500+
>>>> boards through it.  I've lost count.  Others bitch but I have not had
>>>> a problem with it.  The keyboard debounce is not great and a couple
>>>> other minor issues but it does work.
>>>
>>> This seems a bit larger than the other unit mentioned in this thread
>>> -- closer to 1 sq ft.  Still a bit smaller than I would like, though. 
>>> (buy two??)
>>
>> I have an extra one as a spare.
> 
> Have you had a need for it in that capacity?  I.e., something breaking
> in the "primary" unit that necessitates calling on the "secondary"?
> 

No not yet.  Many times what I am building is on a tight shipping
schedule.  If the oven broke I'd be back to the hot air gun and there 
is now way I would make the schedule.  So I bought a spare.


>> Total cycle time for a board/panel
>> can be in the 10 minute range with cool down.  The good thing about the
>> Amtech LF-4300 is the long work time.  I can get>6 hours out of it.  I
>> have thought about using both ovens but I dont feel like running
>> another 20A circuit.  I could have one baking while the other is
>> cooling down.  The problem I found was not the time in the oven. It's
>> the time to paste and stuff the board or large panel.
> 
> Yes.  But you have to have a place to "accumulate" each stuffed board
> while awaiting their turn in the oven.  I'd prefer to just use the
> oven's tray for that purpose.  And, not have to *attend* to the oven by
> putting it "in use" before I've finished stuffing all of the boards.
> 
> [Returning to my cookie/cheesecake analogy:  it would be A LOT easier to
> have 10 cookie sheets and an oven that could accomodate all of them
> (cooking each with the same general thermal characteristics) than to
> have to feed a new sheet into the oven -- and clear off the recently
> withdrawn sheet -- every 4.5 minutes!  Or, shove them through on a
> CONVEYOR!!]
> 

I have some ESD stackable trays I use.  My sequence is I paste maybe
8 or 10 boards and put them in the trays.  I have a little "box" that
keeps them about 65F to help with the paste life.  I stuff one and
into the oven.  While it bakes I start stuffing another, etc. Or 
depending on the board I might stuff them all.  The stack trays 
really help.

The trick is to balance your paste life with how long it takes
to stuff and bake.

Trying to do something like an oven rack is tricky and would be
almost impossible with a double sided board.  You have to be
able to control the heat on the "other" side.  Surface tension
only goes so far competing with gravity.

I understand what you want to do, like baking loaves of bread. Not
that easy keeping the temps right.  Take a look at your paste
temp profile.  You need to ramp to, say 220C and then make that
bump to 240C in 15-30 seconds depending on your profile.  Then ideally
need to bring that back down in 15-30 seconds.

>> I have a small air powered
>> paste dispenser with a foot pedal.  For dense and or large boards that
>> gets old quick.  I'm more than happy to spend the $100 or so for a
>> stencil. Your time can go from 30 minutes squirting pads to 3 or 4
>> minutes.  Sometimes it takes longer to clean up the stencil than to
>> actually paste the boards.
> 
> Yes.  My current goal is to try to get the number of different artworks
> down so the "overhead" per design doesn't get silly. E.g., making qty
> *1* of a board starts to leave you scratching your head re: the costs
> involved.
> 
> Currently, I have only one design that *requires* qty 1.  And, it's
> functionality/feature set is generic enough that I can probably *buy*
> something COTS that is more cost effective from top to bottom (as long
> as I can get complete docs so I can code on bare iron).
> 
> But, there are still some designs that are qty 5 or qty 3... Amortizing
> a $100 stencil over 3 boards -- each with $20-50 of components -- just
> never feels "right"!
> 
>> Wish I had the volume to justify a setup like JL has out there in
>> earthquake country.  That's a sweet line.
> 
> I don't want to build boards for a living.  That's a *job*!  :>
> 
> Likewise, I'm not fond of doing layouts.  But, it's a lot easier than
> having to hover over another engineer's shoulder advising him of
> mechanical interference issues.  Or, having to abandon a particular
> approach because "things don't fit" -- instead of being able to make a
> design change on-the-fly.
> 
> Rather, I will build boards (and do layouts) of necessity to be more
> agile in my design/fab process.  Once "done", dispose of all the
> associated kit -- having extracted all the necessary value from it.
> 
>>>> It's not a $30K reflow oven so it does have some limitations.  Temp
>>>> control is OK but does tend to over shoot by about +10C when trying
>>>> to ramp up.  You can program 2 custom profiles.
>>>>
>>>> Runs off 110V 15A circuit.
>>>>
>>>> I have learned not to shove it full of boards.  You have to subtract
>>>> about 1" from the sides as keep out.  If you go this route get the
>>>> larger T-962A.
>>>
>>> <frown>   Is this a typo?  "LARGER t-962A" (isn't that what you were
>>> describing already?)
>>
>> I mean the larger T-962A vs the T-962.
> 
> Ah, OK.  I found a T962c which is apparently larger still.  (I hadn't
> noticed the size difference between 962 and 962A -- I assumed the former
> was just a typographical omission)
> 
>>>> For me it was a buy vs build decision and buy won out.  At the time
>>>> when I bought it I simply did not have time to be screwing around
>>>> with a toaster oven approach.
>>>
>>> I don't want to build.  I don't want to use paste gun and Leister.  I
>>> don't want to be in the board fab business.  I don't want to save
>>> pennies and waste hours.
>>>
>>> OTOH, I want to be able to assemble boards *when* I want them without
>>> having to send off to a fab house (esp for small quantities).  But, I
>>> don't need to construct an "out building" just to house a small fab!
>>
>> Mine is on a small roll around cart in the garage.  You will stink up
>> the house if you use it inside (any oven technique). Need ventilation.
> 
> I have a small room off the garage that I will probably repurpose for
> this use.  Venting to the outdoors will be relatively easy.  And, it is
> effectively isolated from the interior of the house.  Easy to get
> necessary power.  Etc.
> 
> Or, if that doesn't work out, set it out in the yard where the drop for
> the kiln is located.  (i.e., it would be really nice to just be able to
> load up a drawer *ONCE* and carry it to the oven)
> 
>> For<100 or so pads per board, a paste dispenser is not too bad.  I use
>> one of those portable air tanks.  It will last longer than my butt will
>> take sitting there squirting boards, but it still gets old quick.
> 
> Did I mention "that's a JOB"??  :>  OTOH, you get to see the real
> manufacturing problems that your design and layout pose.  Far more
> helpful than offloading those problems to a fab house and never
> realizing that "a little tweak" could significantly improve the
> process/product.
> 
> My smallest boards probably barely fit the 100 pad criteria. 1.25" x
> 2.5" components double-sided.  But, I need three (different layouts) or
> four to complete "one device/design" (i.e., I'm severely constrained on
> the overall device envelope)
> 
> And, there is a fair bit of followup work involved (thru-hole parts,
> socketed devices, etc.)
> 
>> The dispenser is tucked away on the work bench. I have done the hot air
>> gun thing.  I'm glad it just sits on the shelf now.
> 
> Mine (leister) is more than 20 years old.  Bought it for one-off
> prototype builds and occasional rework.  Well worth the investment.
> OTOH, not something I would want to make a career out of!
> 
>>>> That's my story.  Like I say, others bitch it's just Chinese junk and
>>>> it does have some warts but it works for me.
>>>>
>>>> I use Amtech LF4300 paste.  If you are going to make more than just a
>>>> few of the same board it is well worth the money to get a proto
>>>> stencil.
>>>
>>> Most of my designs are small quantities - five or six pieces. Biggest
>>> (quantity) one is ~75 pieces.  I am currently trying to merge designs
>>> and/or support differential stuffing to cut down on the number of
>>> layouts, etc. and drive the number of instances up.  But, I am *sure*
>>> I will never get to JUST one or two designs... there are too many
>>> physical constraint differences as well as cost, performance, etc.
>>>
>>> (optimizing designs also "wastes" my time, beyond a certain point.
>>> Easier just to settle on a reasonable compromise and let the
>>> quantities be what they may be)
>>
>> I have found that trying to do QFNs or .5 pitch is difficult without a
>> stencil.  Others report they can do this small but I always get too
>> much paste and bridges.
> 
> Yes.  This only gets worse with age (vision, tremor, patience, etc.)
> 
>> If I'm going to, even "someday", do more than 10 of some board I get a
>> stencil.  It just makes life so much easier.
> 
> In my case, I may build "many" of a particular design, but seldom "all
> at once".  E.g., it's one thing to buy enough bare boards to build 75
> (or even *10*) of something.  Quite another to also commit to the
> components and *assembly* before you have thoroughly evaluated and
> characterized the design!
> 
> OTOH, building *one* prototype of each is hardly worth the effort and
> expense.
> 
>> I generally use Stencils Unlimited.  Never had a problem with them.
>> Upload your paste layer gerbers and 4 or 5 days later UPS shows up. I
>> have noticed a lot of the board houses are now offering proto stencil
>> service.  I think they all just send it out to the same place.
> 
> I wonder if *any* "laser cutting service" could do a similar job?

Maybe.  But I dont think it's worth the trouble.  My stencils are
normally 5mil stainless.  The way I understand it (and could be
wrong) you also have to post process the cut to clean it up so the
release is better.  I just order them and the stencil guys tell
me the best choice.  I have no desire to become a stencil expert.

-- 
Chisolm
Republic of Texas

Hi Joe,

On 9/5/2014 9:05 PM, Joe Chisolm wrote:
> On Fri, 05 Sep 2014 13:52:12 -0700, Don Y wrote:
>> On 9/5/2014 1:04 PM, Joe Chisolm wrote:
>>
>> [elided]
>>
>>>>> I have a T-962A that I've used for several years.  Probably put 500+
>>>>> boards through it.  I've lost count.  Others bitch but I have not had
>>>>> a problem with it.  The keyboard debounce is not great and a couple
>>>>> other minor issues but it does work.
>>>>
>>>> This seems a bit larger than the other unit mentioned in this thread
>>>> -- closer to 1 sq ft.  Still a bit smaller than I would like, though.
>>>> (buy two??)
>>>
>>> I have an extra one as a spare.
>>
>> Have you had a need for it in that capacity?  I.e., something breaking
>> in the "primary" unit that necessitates calling on the "secondary"?
>
> No not yet.  Many times what I am building is on a tight shipping
> schedule.  If the oven broke I'd be back to the hot air gun and there
> is now way I would make the schedule.  So I bought a spare.

OK.  So, in your opinion, it isn't the sort of device that just
falls apart when you peel the chinese cardboard (box) off of it!

>> Yes.  But you have to have a place to "accumulate" each stuffed board
>> while awaiting their turn in the oven.  I'd prefer to just use the
>> oven's tray for that purpose.  And, not have to *attend* to the oven by
>> putting it "in use" before I've finished stuffing all of the boards.
>>
>> [Returning to my cookie/cheesecake analogy:  it would be A LOT easier to
>> have 10 cookie sheets and an oven that could accomodate all of them
>> (cooking each with the same general thermal characteristics) than to
>> have to feed a new sheet into the oven -- and clear off the recently
>> withdrawn sheet -- every 4.5 minutes!  Or, shove them through on a
>> CONVEYOR!!]
>
> I have some ESD stackable trays I use.  My sequence is I paste maybe
> 8 or 10 boards and put them in the trays.

So your boards tend to be small-ish?

> I have a little "box" that
> keeps them about 65F to help with the paste life.  I stuff one and
> into the oven.  While it bakes I start stuffing another, etc. Or
> depending on the board I might stuff them all.  The stack trays
> really help.

I was planning on using the drawer from the oven to "accumulate"
the stuffed boards.  So, I need space for the oven and enough
elbow room to stuff *one* board (at a time).

> The trick is to balance your paste life with how long it takes
> to stuff and bake.

I am hoping to decouple the two -- by not caring how long the
bake cycle takes as I'm "done" stuffing before it *started*
(so I don't have to drop what I am working on to attend to the
oven's call).

> Trying to do something like an oven rack is tricky and would be
> almost impossible with a double sided board.  You have to be
> able to control the heat on the "other" side.  Surface tension
> only goes so far competing with gravity.

"Oven rack" meaning *toaster* oven rack?  I.e., have you had problems
doing double-sided in your kit?  (do one side at a time -- heatsinking
the inactive side?)

> I understand what you want to do, like baking loaves of bread. Not
> that easy keeping the temps right.  Take a look at your paste
> temp profile.  You need to ramp to, say 220C and then make that
> bump to 240C in 15-30 seconds depending on your profile.  Then ideally
> need to bring that back down in 15-30 seconds.

As I mentioned elsewhere, external air handler would be an ideal
way of doing this!  Change air temperature nearly *instantly*!
Of course, more wasteful of power and you'd need a place to exhaust
all that process air...

>>> I generally use Stencils Unlimited.  Never had a problem with them.
>>> Upload your paste layer gerbers and 4 or 5 days later UPS shows up. I
>>> have noticed a lot of the board houses are now offering proto stencil
>>> service.  I think they all just send it out to the same place.
>>
>> I wonder if *any* "laser cutting service" could do a similar job?
>
> Maybe.  But I dont think it's worth the trouble.  My stencils are
> normally 5mil stainless.  The way I understand it (and could be
> wrong) you also have to post process the cut to clean it up so the
> release is better.  I just order them and the stencil guys tell
> me the best choice.  I have no desire to become a stencil expert.

Ditto.  I don't want to be a reflow expert, either!  Rather, like
every other skillset, learn just what I need to do what I want and
avoid the annoying details that address "the last 2%".

(sigh)  Perhaps I should start calling in some favors.  After all,
folks forget they owe you if you leave them "banked" too long!  ;-)
And, it would be really annoying to discover folks retiring out
of positions where they can be of help!

I guess I will have to deal with the dreaded telephone this weekend...

Thanks for your comments!
--don

P.S.  Any suggestions re: the T-962C I mentioned?  "A bigger version
of the A?"  Or, does the design not scale well??

On Fri, 05 Sep 2014 23:05:12 -0500, Joe Chisolm
<jchisolm6@earthlink.net> Gave us:

>
>I have some ESD stackable trays I use.  My sequence is I paste maybe
>8 or 10 boards and put them in the trays.  I have a little "box" that
>keeps them about 65F to help with the paste life.  I stuff one and
>into the oven.  While it bakes I start stuffing another, etc. Or 
>depending on the board I might stuff them all.  The stack trays 
>really help.
>
>The trick is to balance your paste life with how long it takes
>to stuff and bake.


  Paste life includes all time until the reflow run itself.

  I am sure lead free has longer open air time than the old stuff.

  The old stuff made way better solder joint IMO though.

In article <lue55k$g41$1@speranza.aioe.org>, this@is.not.me.com says...
.... 
> P.S.  Any suggestions re: the T-962C I mentioned?  "A bigger version
> of the A?"  Or, does the design not scale well??

Have a look at these folks and their description of differences

https://www.estechnical.co.uk/blog/entry/t962c-reflow-oven-troubles

In their view it is underpowered has the same heater and fans as
T-962A trying to heat a larger volume.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.pcserviceselectronics.co.uk/pi/>  Raspberry Pi Add-ons
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.badweb.org.uk/> For those web sites you hate

On 2014-09-06, Joe Chisolm <jchisolm6@earthlink.net> wrote:
> On Fri, 05 Sep 2014 13:52:12 -0700, Don Y wrote:
>
>> 
>> I wonder if *any* "laser cutting service" could do a similar job?
>
> Maybe.  But I dont think it's worth the trouble.  My stencils are
> normally 5mil stainless.  The way I understand it (and could be
> wrong) you also have to post process the cut to clean it up so the
> release is better.  I just order them and the stencil guys tell
> me the best choice.  I have no desire to become a stencil expert.

for something you're only building one of stainless seems a needless
expense, polycarbonate or paper might be better priced and
sufficiently durable.

-- 
umop apisdn


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On Fri, 05 Sep 2014 23:04:22 -0700, DecadentLinuxUserNumeroUno
<DLU1@DecadentLinuxUser.org> wrote:

>On Fri, 05 Sep 2014 23:05:12 -0500, Joe Chisolm
><jchisolm6@earthlink.net> Gave us:
>
>>
>>I have some ESD stackable trays I use.  My sequence is I paste maybe
>>8 or 10 boards and put them in the trays.  I have a little "box" that
>>keeps them about 65F to help with the paste life.  I stuff one and
>>into the oven.  While it bakes I start stuffing another, etc. Or 
>>depending on the board I might stuff them all.  The stack trays 
>>really help.
>>
>>The trick is to balance your paste life with how long it takes
>>to stuff and bake.
>
>
>  Paste life includes all time until the reflow run itself.
>
>  I am sure lead free has longer open air time than the old stuff.

Perhaps but lead-free has a very tight temperature profile.  The
difference in temperature between the solder melting and the parts
wilting is very small and short (time).  The PPoE had a lot of trouble
with their lead-free solder process in a four-stage oven.  LEDs,
aluminum capacitors, inductors, and QFNs were the biggest problems.
Balancing the profile between the needs of all of these was like
balancing a pencil on its point.  They bought a used multi-stage oven
(eight or eleven, can't remember) in 2010, when manufacturing
equipment could be had for pennies on the dollar, and the problems
went away.

>  The old stuff made way better solder joint IMO though.

Far harder to get the same quality, that's certain.  Harder to
inspect, too.