"So i want to have my own SMT assembly line"

[Kjelt]

My simple 'bucket' machines dont' loose much at all.   The main vapour cloud only goes about 50mm above the bottom of the tank,  theres a small amount of 'soft' vapour that just condences on the sides of the tank or the lid and falls back into it.     A very small amount sometimes is on the boards, but most of it has evaporated off the board, and it realy doesnt become and issue.

You have to weigh it I guess , but then if you have to weigh it , it is small potatoes.
BTW: this topic seriously needs some pictures 

[mrpackethead]

I hadn't even considered if data sheets mentioned the process. If it's so safe why would device manufacturers specifically exclude it?

I think its all about the time/temperature profiles. With vapour phase the vapour can be just 10C above the melting point of the solder, rather than the 30C or more you see in convection/IR systems. However, the peak temperature is sustained for longer. Many electrolytics react badly to the soldering temperature being sustained for too long.

My solder melts at 217, ( Henkel GC10 ), and I'm using Galden LS230.  ( 230C ).   I only hold the peak for about 20s, and then start cooling to try to get a 4C/s drop off to start with and then down to about 1-2C/s.   Cooling has been the hardest part though.    The old IEMES system had a set of fans that basically blew air over the outside of the tank,   rememebering that stainless steel is NOT a good conductor, and the way the fans where set up, they were mostly restricted.    ( I removed the metal grill, increase the outlet port sizes )..     I've tryed  using water which is pumped up to a leaky pipe, so water flows all over the outside of the tank walls.  Its taken a bit of effort as you have to keep the water off the electrical parts!      I'm thinking that it may actually be better replaced by simply putting a coil of thin wall copper pipe in the tank, and passing water through it when cooling is required.

[mrpackethead]

The other major reflow vendors either don't or barely offer VP, it has been the next big thing for years, hasn't happened yet. (IR by contrast is so dead it is barely worth mentioning).

There seemed to be quite a lot of high vapour phase lines being installed in Chinese a couple of years ago, and the stated reason was generally energy efficiency. I don't know if that trend has continued.

If you could run it continously, it woudl be verty efficent.   running it the way i do. Its not at all efficent!

[mrpackethead]

The Vapor Phase fluid is around $260/1kg from what I saw after a brief scan of suppliers.

That kind of shows the benefit of a closed system that recovers as much of the fluid as possible. I guess as @mrpackethead said - if you are not in a big hurry the entire thermal cycle can happen with the chamber closed. That, of course, allows the fluid to condense before the PCB is removed.

A 20min cycle would not be much of a problem with the way I work. Better than spending >$25k++ anyway.

yes, the Galden is NOT cheap.     But losses are low.  I've done 5000+ Panels ( A4 size ) in ours, and I've only lost about 2kg of material.

[mrpackethead]

My simple 'bucket' machines dont' loose much at all.   The main vapour cloud only goes about 50mm above the bottom of the tank,  theres a small amount of 'soft' vapour that just condences on the sides of the tank or the lid and falls back into it.     A very small amount sometimes is on the boards, but most of it has evaporated off the board, and it realy doesnt become and issue.

You have to weigh it I guess , but then if you have to weigh it , it is small potatoes.
BTW: this topic seriously needs some pictures 

The loss is low enough that its not worth worrying about.   5000+ panels and a loss of about 2kg

[rx8pilot]

yes, the Galden is NOT cheap.     But losses are low.  I've done 5000+ Panels ( A4 size ) in ours, and I've only lost about 2kg of material.

Sounds like around $.10 per panel - not exactly a financial stress point. Good to know!

Does Galden have a shelf life, pot life, cycle life, etc? Does it go bad sitting in the machine for weeks at room temp? Any maintenance like filtering, skimming, etc?

[coppice]

Sounds like around $.10 per panel - not exactly a financial stress point. Good to know!

Gee, you guys are rich. Do you realise how much negotiation most customers will engage in to drive just one cent out of their BOM?

[mrpackethead]

Sounds like around $.10 per panel - not exactly a financial stress point. Good to know!

Gee, you guys are rich. Do you realise how much negotiation most customers will engage in to drive just one cent out of their BOM?

Its for this exact reason i've followed through with using VP.  For my particular set of circumstances, it provides me the most cost effective overall solution.

- I dont' spend any time having to profile PCBs for Reflow.
- I get really good quality joints ( oxygen free environment )
- I have less issues.. 

Anything that saves time is the thing that saves me the most money.

[rx8pilot]

Gee, you guys are rich. Do you realise how much negotiation most customers will engage in to drive just one cent out of their BOM?

Yeah, totally. My Gulfstream 650 was in the shop, but I was able to use my spare jet to go to a party in Tokyo for the weekend. 

Seriously - I carefully consider my BOM cost like anyone but labor and rework tend to dominate. Anything that makes the process faster and more reliable is worth a lot more than $.10 per panel. Private jets are expensive, I have to keep my lifestyle moving at mach .94 and vapor phase will get me there, lol.

I wish I had logged the time I have spent dealing with solder problems this past year. Those problems are partially print/paste related and partially oven related. This conversation is encouraging me to look closer at VP, at least as an experiment.

[mrpackethead]

Vapor phase is great on paper and seemingly addresses many issues (as does Vacuum) however it does have a weakness, very few electrolytics can handle the process with most specifically excluding it as a suitable process in the datasheet.

I checked in with Panasonic on this topic today and found that they have covered this in their datasheet.


(6) VPS (Vapor Phase Soldering) reflow can cause significant characteristics change and/ or mounting failure due to
 deformation by acute temperature rise. VPS is acceptable provided that the process does not exceed recommended reflow profile and temperature rise
 is less than 3degC/sec.

Since i'm not dropping my boards into the vapour ( like the commerical machines do ), my Reflow profile is not goign to be nearly as steep' as it woudl be if you did just drop it in the tank, i'm nmore like 2/s

[rx8pilot]

From what I read - it seem that the commercial machines allow the system to hold a pre-heat temp that are suitably low to avoid thermal shocking parts. Then ramp at a chosen rate with the usual profile programming.

[D3f1ant]

Was having a look at the asscon machines. They have basic ramp rate profile for the entry level machines like the VP450 and 510, and what looks more standard profiling for the bigger machines like the VP800. Not exactly sure how they acheive this...but at E$40k I'm sure they pack some technology into them...to expensive to me
 

[Kjelt]

Look at youtube.
The asscon and IBL machines lower the board and monitor the temperature to follow the profile.
They certainly don't drop it in.
Perhaps the cheap machines that look like a horeca "au bain marie" machine do.

What is interesting is that both machine makers use vacuum at the end of the process.
I don't understand this since in vacuum a liquid will boil earlier at lower temperatures but perhaps this is not vacuum but lower pressure sucking the fumes from the chamber and cool the fumes down. It would be interesting to see/read more about how this last step is achieved.

[SMTech]

Well if you take convection ovens:

TWS £15-20k
Essemtec RO-400 ~ £20k
Similar Chinese but with Mesh AND conveyor  and extras same price.
Folungwin starts around £30k- paper spec rivals something like a Soltec/BTU
Basic Heller starts around £35k
BTU starts around £50k

The more expensive they get the bigger and more complicated, but the warranty also improves e.g lifetime heater and blowers on the BTU. Cheap ovens just blow hot air, they are simply a hot tunnel with controls. As you move up you gain all sorts of thing from complex air redistribution, logging, extra zones, filters, heat capacity, center support rails, UPS (the last thing you want is for your products to stop in the oven in a powercut), clever profiling software

[Kjelt]

Back to VP interesting read:
http://www.torenko.com/pdf/Todays-Vapor-Phase-Soldering-Tech-Paper.pdf

[mrpackethead]

Sorry, 'Drop it in' was not a good term.  I should have said.. "lower it into the vapour".    If you took a cold board and just dropped it into the vapour cloud quickly, the temp rise rate would likely be very high, but if you did it slowly in a controlled way, it would be quite differnet no doubt.

What i know about my 'bucket' heater.. ( its about 400mm deep ).      The amount of energy you stick in, will determine the height of the 'thick vapour'.     once its at 'temp', if i run it at ~300W it will create a cloud that is about 20mm thick.  If its 600W, it will create a cloud 60mm thick.  Above the thick vapour is a 'soft' vapour zone, where the temp is around 150-190C .. Above that is an area of warm air.   ( 80-120C or So )..  I think that in some of the commerical machines they use these varying temp zones to create a profile, by progressively dropping the board into the hotter areas.. ( counter intuivate, that the hotter area is at the bottom )..   They can keep the vapour cloud going, and control temp on the board by height.

In a bucket heater, you can acehive profile, by varying the amount of energy that you put into the system at any given time.  This is easy, you just need a thermocouple probe at board height, and a way to control the amount of energy you are putting into the system. ( if you are using an AC heater, you can just use some Zero crossing Triacs,  I'm controlling power in over 2seconds. ( 50Hz ) so i have 1% resolution.. Theres a lot of thermal mass in the system, so 2 seconds its not that long.     

Sorry been just really busy today making stuff, so will try to get some photos/info together, this weekend.    My new tanks are made from Stainless Steel.  It was made from sheet, water jet cut, and then folded, and welded..   

[Kjelt]

What is interesting is that both machine makers use vacuum at the end of the process.
I don't understand this since in vacuum a liquid will boil earlier at lower temperatures but perhaps this is not vacuum but lower pressure sucking the fumes from the chamber and cool the fumes down. It would be interesting to see/read more about how this last step is achieved.

Found the explanation:

A special form of vapor phase soldering is vacuum vapor phase soldering. After the soldering paste has completely melted, the air is pumped out in the process chamber. The negative pressure ensures that gaseous inclusions are largely displaced to the outside in the soldering points and thus separated from the soldered joint. The result are solder joints without voids. This technology is particularly advantageous when the solder joints are to dissipate heat, since air inclusions increase the thermal resistance of the solder joint. In addition, voids impair the mechanical load-bearing capacity.

So without the low vacuum , VP soldering has a high risk of introducing voids in the solderpaste, esp. critical for cooling pads and BGA's , see:

http://www.circuitinsight.com/pdf/void_free_soldering_new_vapor_phase_smta.pdf