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QFN Rework Issues

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Hello SMTA. I'm having issues reworking QFNs inside housin... - Feb 12, 2019 by SMTA-Joe   via SMTA

Thank you! ... - Feb 13, 2019 by SMTA-Joe   via SMTA


SMTA-Joe

#81933

QFN Rework Issues | 12 February, 2019

Hello SMTA.

I'm having issues reworking QFNs inside housings with a much higher thermal mass than any typical PCB.

We have had demonstrations in-house using BGA rework stations that simply don't get the job done. The problem is threefold:

1) the area within the housings is too small for nozzles to focus on the specific component. I believe IR is the way to go to focus on the component.

2) the thermal mass of the housing is too great for IR bottom heaters to sufficiently heat the module. We've had success using a standalone JBC hot air machine with the module placed on a hotplate. But it doesn't appear that BGA rework stations have any kind of conduction heating surfaces that would replicate a standalone hotplate.

3) We are currently hand-placing these components, then using a hotplate and hot air to re-install. This often leads to shorts due to alignment issues that require repeated rework. This is why I would prefer to look into getting a BGA rework machine for it's alignment capabilities.

Any guidance would be appreciated. This is becoming a greater and greater challenge for us and we need a solution.

Thanks!

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#81946

QFN Rework Issues | 12 February, 2019

Hi Joe,

I work for an equipment manufacturer and we have processed RF housings before so I know they are challenging in terms of thermal mass. Let me know if you are available to discuss your application details and what would be a good email address to reach you.

Steve

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#81950

QFN Rework Issues | 13 February, 2019

PACE produces several BGA Rework Systems that are robust enough for your application. Go to paceworldwide.com/bga to find out about them. I recommend you look at our new TF2800 BGA/SMD Rework Station as it has a massive preheater which is likely to get the job done.

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SMTA-Joe

#81951

QFN Rework Issues | 13 February, 2019

We recently had an in-house demo with the smaller IR bottom heater PACE machine. The machine was barely able to remove some components, but could not replace new ones at all. Also, the nozzle for the hot air would not fit in the tight areas of the housing.

We believe IR for the top heating is the way for us to go as it can focus much more narrowly on the desired location.

We've been experimenting with a standalone IR heater to see what temperature we can get the housing up to. The heater we're experimenting with has a max setting of 200c. This only got the desired application site to ~100 +/-.

With a hot air machine set to over 250c this wasn't enough to reflow SN42 solder paste, which should melt around 140c.

Traditionally when we hand-place components for reflow we bring modules up to 165c on a standard hot plate to ensure thorough heating and good reflow.

Now with our designs incorporating so many QFNs we need to evolve our rework methods.

I'm experimenting today with a standard hotplate just to see what the minimum temp needed is to reflow SN42 using a JBC hot air machine.

I looked at the spec on the model BGA rework station you recommended, and the bottom preheater only sets to 220c. I do not know if this would allow our modules to reach the necessary temp to perform the desired rework.

Are there models that come with hot plate preheaters instead of IR? Or models that are just standalone alignment/placement cameras that we could add a hotplate to in order to achieve any temperature we require?

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SMTA-Bob

#81953

QFN Rework Issues | 13 February, 2019

With any board assembly or unit that has a high mass its also possible to just place it in an oven to raise the core temperature of the mass that is holding back the rework

This works for any difficult to rework product. It would be useful to have a photo of the product to be more specific. Otherwise the rework procedure to remove and replace would be the same. Every engineer has a preference for either IR or convection

bob@bobwillis.co.uk

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SMTA-Joe

#81954

QFN Rework Issues | 13 February, 2019

*UPDATE*

I decided to modify the experiment slightly by forgoing my attempt to achieve reflow with the component. Instead I applied SN42 paste directly to the pad and attempted reflow of the paste by itself.

The end result is as follows:

Hotplate set to 150c Thermocouple on module read 127.4c Hot Air set to 250c w/ 50% airflow

After 2min soak, solder melted perfectly.

I am comfortable in assuming the addition of a component wouldn't have effected this too greatly, but I would probably want to achieve a temp reading of 130c on the module.

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SMTA-Joe

#81955

QFN Rework Issues | 13 February, 2019

I will look into using an oven to raise the module's temp when I have the chance. This could be our only way to use existing technology that only allows for temps below what we're seeing.

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#81956

QFN Rework Issues | 13 February, 2019

The QFN will add an insignificant amount of thermal mass since its all in the housing. You just need to make sure the package does not exceed the recommended peak and duration so as not to damage the die internally. Usually the limit is around 250-260C.

Preheating on a hot plate or in a enclosed oven chamber is effective just consider the process of handling the housing as you take it your rework station for optical alignment. Also, consistency in the profile - you will likely need to track the housing temperature with every profile on the rework station.

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#81957

QFN Rework Issues | 13 February, 2019

The TF2800 features a much more powerful 1900W bottom-side preheater which incorporates 7 independently activated (via software) IR emitters. The preheater is also height adjustable to allow it to get closer to the pcb to provide more aggressive thermal transfer on higher mass pcb's and components. Designed for larger heat-sinking boards with high mass, the TF2800 will definitely perform QFN reflow much more effectively than previous PACE models.

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#81958

QFN Rework Issues | 13 February, 2019

I believe the end user is working with an aluminum housing - something like this http://www.boainc.ca/UserFiles/product/JP01-600x490.jpg with a PCB mounted inside. Not very user friendly material especially for IR as its reflective.

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SMTA-Joe

#81960

QFN Rework Issues | 13 February, 2019

Correct. silver-plated Aluminum in fact.

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SMTA-Joe

#81962

QFN Rework Issues | 13 February, 2019

Would we be able to schedule a demo for this model? If so, would this have the IR top heater as well?

In the event IR bottom heating does not work, are there models with alignment/placement assistance that we can just use with a conventional hotplate?

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#81963

QFN Rework Issues | 13 February, 2019

If you could send your email address to acaplan (AT) paceworldwide (DOT) com, I could arrange a demo through one of our Representatives.

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SMTA-Joe

#81965

QFN Rework Issues | 13 February, 2019

I actually have a quote for the larger TF2800 from the rep that came to do the demo on the smaller model. There was talk of us sending hardware to PACE for them to see if they could get the larger model to work for us, but the decision was made not to release our hardware to anyone. We would like to have the demonstration in-house.

Should I work backwards from the quote and restart dialogue with the rep?

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#81966

QFN Rework Issues | 13 February, 2019

Out of curiosity is it actual silver or silver colored - ie. Nickel? Are you out of NJ by any chance?

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SMTA-Joe

#81967

QFN Rework Issues | 13 February, 2019

It is actual silver. And we're on Long Island.

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#81969

QFN Rework Issues | 13 February, 2019

I'll contact the Rep and PACE Regional Manager and get back with you.

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SMTA-Joe

#81975

QFN Rework Issues | 13 February, 2019

Thank you!

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#81978

QFN Rework Issues | 13 February, 2019

BTW - in our testing on housings with Sn42Bi57 paste, it took 240 seconds to reach 140C on an aluminum module with a mass of 0.75 lbs. This was from ambient and only using machine preheating before having the top heater turn on to peak at 162C. Same paste and procedure with an aluminum microwave housing that has a mass of 1.4 lbs took 420 seconds.

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SMTA-Joe

#81979

QFN Rework Issues | 13 February, 2019

What machine was this with? A BGA rework station?

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SMTA-Chris

#81982

QFN Rework Issues | 13 February, 2019

We’ve done similar projects. FR-811 with camera system for alignment. More cost effective than split vision. Bottom heat uses solid surface for contact heating similar to heating microwave module chassis.

Our rep can arrange a demo if you haven’t settled on a solution.

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SMTA-Joe

#81988

QFN Rework Issues | 14 February, 2019

This sounds like a workable solution in line with what I'm looking for. What company do you represent?

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#81991

QFN Rework Issues | 14 February, 2019

Here are the details on the rework station: https://atco-us.com/products/item/1-at-gdp-smd-bga-placement-rework-stations

If you have interest in a reflow oven to preheat or solder within microwave housings take a look at https://atco-us.com/index.php/products/item/5-pro-1600-smt-reflow-ovens

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SMTA-Joe

#81996

QFN Rework Issues | 15 February, 2019

SMTA-Chris, can I have more info about these items, and rep contact info?

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#82440

QFN Rework Issues | 25 April, 2019

Joe,

If you havent already, please take a look at our Focused IR Rework Stations. I am confident we have a machine which will be perfect for this aplication, you will also get the benefit of a visible heating area, there is no more Nozzles/Guess work involved. http://www.pdr-rework.com

All the best.

Attachments:

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#82453

QFN Rework Issues | 26 April, 2019

Check out our line of Shuttle Star BGA Rework Stations.

We just sold two model SV560 to a client with the same problem.

Our prices include training on machine set up, profile development, process implementation and an operator certificate.

We have been providing rework services and training since 1991 and became a distributor of Shuttle Star in 2011. We use the same machines we sell in our rework facility. Get your training from the BGA Rework Pioneers.

Send us your board and we will provide a sample rework with demo video using your product.

Sincerely. Dennis O'Donnell Vice President Precision PCB Services, Inc. Now with offices in Sacramento and Dallas

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