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Multiple Resistor Rework

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#62557

Multiple Resistor Rework | 30 August, 2010

Hello,

I have been tasked with finding a solution to rework 242 boards that have 34 incorrect 0603 resistors placed. These resistors are placed throughout the board and are surrounded by other SMT components.

If anyone can advise me on a more time effective method of reworking the boards without having to hand solder each resistor individually.

Attached is a .JPEG of the board to rework with the resistors highlighted.

Attachments:

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#62558

Multiple Resistor Rework | 30 August, 2010

We appreciate your desire to find the most time effective method of reworking these boards.

However, we believe that your most efficient method will be to have one assembler remove all of the parts, and a second assembler place/hand solder the parts.

We've done rework of this nature before, and haven't been able to find any better/more accurate method of performing the rework. We've tried removing all the components, applying sticky flux to the board and using a machine to place the new parts...then reflow. In the end, the set-up, programming, removal, placement, reflow, inspection, and touch-up operations have generally taken as much time as removal and hand soldering.

One way to potentially speed this up is to use resistive tweezers for the soldering, rather than two irons. But, I suspect that that will depend on individual solderer techniques and preferences.

cheers ..rob

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#62559

Multiple Resistor Rework | 30 August, 2010

Hi Stephen,

Once they've been soldered down, you're stuck with doing touch labor on each and every one. But you might be suprised how quickly this can be done with the right tools. Are they all the same value resistor? If so, that should make things go even quicker. I would recommend a set of "Hot-tweezers" for the job. Do have access to a pair of these?

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#62560

Multiple Resistor Rework | 30 August, 2010

Yes we have a set Hot-Tweezers. I should have stated above that all of the resistors have been removed already and the new parts are being soldered on. I was just looking for a quicker method of rework. But thanks for the ideas.

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#62564

Multiple Resistor Rework | 30 August, 2010

Lots of small parts, lots of hand soldering, lots of tired eyes inspecting on lots of boards: yields lots of room for error.

How about this: * Part removal ** Cut each resistor between the pads using dykes ** Using a soldering iron [or hot air pen], melt the solder at each connection and flick the half component from the board with the iron [or tweezers] [Remember this is really tedious, shit-work. So maybe assemble a multi-person flow line to crush this part of the project and get it over with. Get a team of 5 qualified people, tell them what needs to be done, let them work the details, and get them what they need, and stay-out of their way.] * Dress the pads where the components were removed * New part attach ** Using an automated dispenser, add solder to each pad where a component has been removed ** Place components using a modified version of the original placement program ** Reflow using the original thermal recipe * Inspect and test according to the original plan

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#62565

Multiple Resistor Rework | 30 August, 2010

Thanks Dave,

I was able to get an automated dispenser to apply an amount of paste that should be sufficent. My only question is should I bake the boards before solder is applied and the boards are reflowed. I ask this because the boards have been sitting out and I do not want to cause any undue damage to the boards. If they should be baked at what temp and how long? I have read in the forum that this should be listed in J-STD-033 but am unable to locate a copy. Thanks for the help.

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#62566

Multiple Resistor Rework | 30 August, 2010

Steve: Yes, you shall bake prior to thermal cycling.

You should be able to download J-033 from JEDEC [ http://www.jedec.org/standards-documents ]. You want "Paragraph 4 Drying." While it's aimed a component parts and not assemblies, J-033 is as good of source for bake recipes as the next.

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