Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Cure/Reflow Profile

Sal

#1827

Cure/Reflow Profile | 22 February, 2000

Guys,

Can I cure adhesive and solder paste in a single operation ? Currently running a double-sided product, paste on one side and glue on the other, Management (YUK!!!) want to run this product simultaenously in the convection oven using the reflow profile ?

Rgds Sal

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JAX

#1828

Re: Cure/Reflow Profile | 22 February, 2000

Sal, To answer your first statement; Yes, you can cure paste and reflow solder using one profile. Question on your second statement; Are you talking about running passive side glue, flipping it over, running active side solder, and then putting the board in the oven??? If so, how are you going to place parts on topside without knocking the bottomside parts off. The viscosity of the glue will not be enough if the board: makes any excessive movements, is too large to avoid bowing while running down the line. If you are able to get parts placed on both sides prior to reflow, is it really worth the headache? That's just my opinion, I could be wrong!

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Sal

#1829

Re: Cure/Reflow Profile | 22 February, 2000

Please let me rephrase the question. Running passive side first and curing the adhesive using a reflow profile derived for 63/37 solder paste. After curing the board is flipped around, pasted and reflowed. My concern is when curing the adhesive using a reflow profile because the product will be getting hotter or faster, will the adhesive not skin over and entrap volatile components ? Will I have some point where the adhesive will not be fully cured ?

Rgds Sal

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JAX

#1830

Re: Cure/Reflow Profile | 22 February, 2000

If you are not placing any parts that need special attention ( BGA, CCGA, etc... ) on topside then it should be fairly easy to create a profile that will work for you. If you are wanting to use the profile you currently have for topside I am not sure without looking at it. It would be best if you created a new one. One small question: What is wrong with having two different profiles. You could easily switch profiles while the first board of topside was running down the line. That's just my .............,

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#1833

Re: Cure/Reflow Profile | 23 February, 2000

Sal,

Jax has a good point about utilizing your multi-profile oven and switching to a different profile. However, since some ovens cause trouble while cooling off and stabilizing, I will assume you do have to use the same profile for whatever reason.

I believe the answer is in your adhesive spec sheet about the damage such high temp may cause. The Loctite 36xx I used would be OK running through the reflow profile. Also, if you're reluctant to change the temperatures, you can still change the conveyor speed and have your adhesive cured. For this case, I don't think you need to check the spec sheet. The only function of the adhesive is keeping the components on the pads in the way they were placed. The higher conveyor speed might even help your cycle time assuming the boards fly through the chip shooters for the adhesive side.

I personally like running primary side first. I can use every possible support in the screen printer since there are no parts underneath yet. Then flip it over (assuming it's not a dense board where you'll have trouble finding spots for the support pins. This trouble also exists if you run secondary side first and can be minimized by preparing a template or determining coordinates for the support pin locations.) and place your chips on glue. There's no stress on the primary side components since a low temp profile will not cause any warpage. If you run the secondary side first, you might have some warpage which may cause vibration (and other) problems during placement.

So, there is more to consider other than "the impact of high temp to your adhesive" when you run the board at the same temps and speed for both sides.

The details of your application may still easily prove my concerns wrong.

Good Luck Erhan

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Dean

#1836

Re: Cure/Reflow Profile | 23 February, 2000

Hey Sal.

Requests I typically receive from management stay just that - requests! Maby its just me but unless you have a single line capable of full double sided capability (printer, P&P, flipper (inverter), printer, P&P, reflow oven) the extra trouble of special (gentle) handling would outweigh the benefits. I hardly see the benefits unless you did not want to spring for a second oven in your "mega line" I mean really, is your cure process the bottleneck? If your talking serious board volume here and your looking for a magic "bean" to extend your line capacity you could set up a couple of "space heaters" facing downward over the boards to tack the epoxy skin. That way you might help prevent the increase of misssing components on the second SMT pass. Not an impossible problem to solve...but odd none the less. Maby a snap cure pressure sensitive adhesive??? Boom-bam-pow cure during pick and place...just place it right the first time!

Give us some future feedback...

Dean

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#1837

Re: Cure/Reflow Profile | 23 February, 2000

We had a similar thread a couple of weeks ago:

Reflow glue and past. - Charlie 12:36:28 02/08/2000

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Sal

#1838

Re: Cure/Reflow Profile | 23 February, 2000

Hey Guys,

Thanks for the input and suggestions. Just been onto the adhesive manufacturer who reckons they should be no issue using a reflow profile for curing his adhesive , as long as the profile duration is not 6 minutes or over, which would bake the adhesive and cause discolouration. Actual duration of the reflow profile is 4.2 minutes.

Sal.

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