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Reflow Problem
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Reflow Problem

by IHeartEngineering on Fri Jan 20, 2012 12:47 pm

Has anyone seen problems with the solder mask cracking and brownish stuff bubbling out from under the mask at the edge like this before?
Doing reflow with an electric skillet, I didn't have a temp gun handy, but I'm pretty sure the temperature was not high enough to normally scorch the boards.

Idea?
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IHeartEngineering
 
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Re: Reflow Problem

by smilingcat on Mon Jan 23, 2012 2:56 pm

Hi,

looks like you fried your board. I would suggest you buy a cheap toaster oven. I use Black and Decker Counter top toaster oven TR0490W. It's only 1200W but plenty strong. And use the toaster oven for reflow only. Do not cook in it. No food what so ever in it. The reflow paste has flux, and other volatile organic compounds which are very bad for your health.

I hope you are not planning on using the skillet for food.

The problem I see is that the heat capacity of the skillet is so much higher than air so when you placed a room temperature board into the skillet, the surface of the board heated very quick while the board itself took some time. You may overheated the solder mask and damaged it. Not to panic, I would still use the board. Reliability may not be as good because of moisture incursion.

Reflow oven uses radiant heat so it heats the surface (solder mask, trace) and the substrate (FR4 fiberglass board) together and evenly.

If you have any other question, let me know. BTW google reflow and I think it has some discussion/explanation on the process.

Lastly, when you cook the board, do it in well ventilated area.
smilingcat
 
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Re: Reflow Problem

by charliex on Mon Jan 23, 2012 4:08 pm

Looks like thermal stress, could be ramping too quickly, too hot and/or too many times, solder mask gets more brittle the more times you heat cycle it.

in my experience scorching can occur about 5-10c over peak reflow temps.
http://032.la - Null Space Labs.
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Re: Reflow Problem

by IHeartEngineering on Thu Jan 26, 2012 11:09 am

We only use the skillet for production, and it usually works well as you don't have to worry about melting connectors.

Our current conclusion is that since there is almost no copper on the back we had trouble getting the top of the board up to temperature without frying the bottom.
On the next version we will try adding a ground plane to the bottom and some vias to see if that improves manufacturability.
IHeartEngineering
 
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Please be positive and constructive with your questions and comments.