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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Reflowing <.032

#32708

Reflowing <.032 | 17 February, 2005

I am having trouble reflowing pcb's that are

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JB

#32710

Reflowing <.032 | 17 February, 2005

We have PCB's that have been poorly designed and do not have enough support.

A quick fix, so they don't bow in the oven, is to set them on a stronger frame, before reflow, from a panel that has been singulated.

Single or double sided?

Hope I interpreted your post right.

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#32714

Reflowing <.032 | 17 February, 2005

I am working on fixturing to keep the pcb/panel from "floating" in the oven. The problem is cold solder/non-wetting on all components. My thoughts lean towards the thin pcb not retaining the "preheat temps" for proper soak/reflow. Any thoughts about the profile?

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Slow Ride

#32718

Reflowing <.032 | 17 February, 2005

Actually the opposite will happen. A thinner board will heat up faster than a thicker board. That aside, it sounds like you don't have any thermal profiling equipment, do you? This is probably a very good investment if you don't. Take all/most of the guess work out of profiling.

A "floating" board? you mean it blows around on the conveyor belt? What type and size oven do you have? Even with a fixture, you should be able to reflow paste.

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JB

#32719

Reflowing <.032 | 17 February, 2005

Most of our profiles are a variation of one another. Depending on the thicknes and density of the PCB, we make the nescessary changes and then we profile it, to make sure it meets our specs.

Check this out:

http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=4214&#Message16583

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#32723

Reflowing <.032 | 17 February, 2005

Slow Ride: I do not have access to external profiling equipment. I am using a profiler included in the Heller 1088 oven software.(Heller 1088 4 zone convection oven) JB: I have started with my original profile and only have difficulties w/<=.032" thickness on two separate customer pcb/panel designs. The .062 pcb/panels present no difficulties. Thank you for the article link...this may be what I am experiencing due to the pcb/panel thickness. I am still remaining open to additional input/ideas. Thanx

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Grant

#32724

Reflowing <.032 | 18 February, 2005

Hi,

I would immediately go out and purchase a profiler as you will save the cost of it on rework savings.

We use a SlimKIC, and the software with it's so good it will let you adjust the oven temps to make your profile fit your paste specifications exactly. We did not have soldering issues, but purchased one because we needed to tighten our process getting ready for lead free. When we ran it showed we were out, even though we thought we were ok, and it reduced the rejects to almost nothing.

We were so happy with it, we went and purchased the prediction software that allows the software to predict the best temps for the oven zones once you run a profile. It works great, and will change your life. We profile everything now.

That's the best thing you can do, and it will eliminate problems like this. I am not sure of the software on the other profilers works the same, and originally we used the built in Soltec profiling, but it was not as good. Its mainly the software that makes the difference, because manually analyzing the profile by looking at temp numbers is too hard to do accurately. Also too slow.

Hope this helps.

Grant

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aj

#32731

Reflowing <.032 | 18 February, 2005

Hi,

As stated by everyone ,you really should have a Profiler and be checking the oven at least once a week.

As a quick fix to Identify if you are reaching reflow temp at all, I would recommend that you buy some Thermal Indicators (temp. stickers)these can be stuck onto the board and it will indicate the max. temperature that the board reaches during reflow.

These cost approx.�7 euro. about 5 USD.

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RDR

#32733

Reflowing <.032 | 18 February, 2005

I would be willing to bet that you are ramping up way too fast and possibly too hot/long of a soak and killing your flux activity. this will give the appearance of "no reflow" due to non-coalescence of the solder balls. check this board with the heller T/Cs and see what it looks like. Tweaking a profile for an .06" thick board to use for a .032" requires significant tweaking. thin boards heat up FAST and get HOT.

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#32735

Reflowing <.032 | 18 February, 2005

Thanx aj and Russ. I will verify my ramp up/down degC/sec and the soak zone peak temp. Fluxes could be burning off prior to activation. I have found access to an old thermal data logger to help verify the Heller thermocouples. I will post updated findings.

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Grant

#32747

Reflowing <.032 | 18 February, 2005

Hi,

Using good profiling makes all the difference. Its not easy, and thats where good software helps make it easy. If it's easy, then you tend to do it often, so things stay good.

I like using this KIC software so much I wanted to take the profiler home and profile a cake I was baking to see what temps it gets to. I was not sure if the thermocouple was lead free though. My next idea was to profile the temp drop of a room temp can of coke once it's put into the refrigerator, and see how long I have to wait to drink it.

Ahh, there's nothing like actually knowing what temperature things get to.

Regards,

Grant

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FW

#32789

Reflowing <.032 | 21 February, 2005

There are some basic suggestions given by everyone that cover most of the requirements. However, I would also like to point out your mention of using a fixture to hold PCB. Are you profiling the board with the fixture? If not, this could be one of the reasons for cold solder.

Regards, FW

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#32801

Reflowing <.032 | 22 February, 2005

I have been profiling with the fixture. I have performed multiple DOE runs and came up with the following with success:

Cooled soak zone to max 150C for approx 100sec. and spiked reflow zone for max temp of 230C, pcb/panel is above 183C for 64sec. The ramp up/down is close to limits at 2.8C/sec. These profile changes have exhibited good flux activity and wetting characteristics.

Thanx for all the suggestions and help !!!!!!

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Reflow Oven

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