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Chip Component Stacking

Chip Component Stacking

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Hi, We have recently been tasked with producing a PCB ass... - May 02, 2017 by Mike

Our customer wanted us to stack two chips but I convinced th... - May 02, 2017 by Travis H

Many years ago (20+) we did this by preassembling the 2 part... - May 03, 2017 by Robl

My machines do this kind of stuff all the time. Usually whe... - May 04, 2017 by robgd3

You could also try some of the 3D MID placement machines - s... - May 06, 2017 by Robl

I did look into the possibility of placing the two component... - May 09, 2017 by Mike

We machine place the first part, then add two dots of dispen... - May 19, 2017 by DeanM

Thanks DeanM. Are you adding the additional flux to the past... - Jun 02, 2017 by Mike

I guess it all depends on volume. If you are talking thousan... - Jun 05, 2017 by PhilC

Mike, The dispensable solder paste is ordered separately ... - Jun 05, 2017 by DeanM

At a past employer we stacked caps and resistors quite regul... - Jun 05, 2017 by Steve Gregory

Mike

#77513

Chip Component Stacking | 2 May, 2017

Hi,

We have recently been tasked with producing a PCB assembly that requires a chip resistor to be stacked on top of a chip capacitor (both are 0603 package size). This becoming a more common practice, I was wondering if anyone has been successful in doing this type of population during the SMT and reflow process without an automated paste dispenser in the mix.

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Travis H

#77514

Chip Component Stacking | 2 May, 2017

Our customer wanted us to stack two chips but I convinced them to let us place them side by side on the same pads. It had the same effect. They were 0603 size components and the pads were big enough that they still passed IPC for solder quality. I just had to over print a little.

Travis

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Robl

#77518

Chip Component Stacking | 3 May, 2017

Many years ago (20+) we did this by preassembling the 2 parts into a mini leadframe with high temp solder paste, which was a pain but then they could be dropped in trays, surface mounted and hit the line clean. I'm guessing you have a low value cap and a high value resistor. Yuk, the joys of RF.

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robgd3

#77526

Chip Component Stacking | 4 May, 2017

My machines do this kind of stuff all the time. Usually when I don't want them to!

But, as long as you can control the z-height during plaacement, I don't see that it should be all that difficult to achieve....depending on package size, of course. Two 0201's on top of eachother might be a challenge for repeatability.

Essentially, it's similar to PoP assembly. I haven't actually done any, but, the concept is there.

As mentioned earlier in this post, placing the parts side by side on the pads ought to be an equitable solution electrically, as well as functionally. Again, depending on package and footprint sizes.

cheers, ..rob

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Robl

#77547

Chip Component Stacking | 6 May, 2017

You could also try some of the 3D MID placement machines - some have dispense heads in with the placement heads, so theoretically you could place on the PCB paste, dispense on the terminals. and place the new part. Yamaha/I-Pulse do a couple: https://global.yamaha-motor.com/business/smt/mounter/s20/ I'm sure others will.

Side by side isn't always enough, sometimes they have to be on top.

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Mike

#77551

Chip Component Stacking | 9 May, 2017

I did look into the possibility of placing the two components side by side, but the land width on the bare board is to small to lend a sufficient solder joint for both parts.

Currently I am looking at a flux coated solder preform that could be placed between the terminations of the two parts. Hopefully it may provide the additional solder needed for acceptable solder joints, as well as the tack strength required to hold the part in place through the process.

Has anyone been successful with this approach?

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DeanM

#77605

Chip Component Stacking | 19 May, 2017

We machine place the first part, then add two dots of dispensable solder paste to the top of the terminations, then hand place the second part on top of the first. Reflow. It works better than hand soldering after reflow.

The solder paste is dispensed from an EFD type dispenser. The paste is the same type as our printable paste but has more flux content so it can be dispensed from 10cc syringes (purchased).

This technique may not be suitable for mid-high volume. We are low volume so it works for us.

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Mike

#77667

Chip Component Stacking | 2 June, 2017

Thanks DeanM. Are you adding the additional flux to the paste that you are dispensing, or are you ordering it separate from what you normally screen?

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PhilC

#77672

Chip Component Stacking | 5 June, 2017

I guess it all depends on volume. If you are talking thousands of PCB's, then automation is best, if possible. Otherwise, hand-soldering them post-production is the obvious solution.

How about bill-boarding them? That way, they would fit on the lands.

Long term solution is to get the customer to redesign the PCB to allow side-by-side placement, either as two seperate lands, or enlarging the current lands to take two components.

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DeanM

#77673

Chip Component Stacking | 5 June, 2017

Mike,

The dispensable solder paste is ordered separately from the printed paste because it has a higher flux content. I would not feel comfortable mixing liquid flux into the printable paste. Ask your paste vendor if they have a dispensable version.

Another reason for the technique I described is that both components are reflowed in the oven. Hand soldering the second part would induce thermal stress to the ceramic capacitor, increasing the possibility of cracking.

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Steve Gregory

#77674

Chip Component Stacking | 5 June, 2017

At a past employer we stacked caps and resistors quite regularly. As some have suggested a dispensable paste was used and dispensed by hand and then the stack was placed. At first it was placed by hand, but then we were able to program our Mydata to place them. There were some stacks that had to be done by hand, the same process was used, but we could not get the machine to place the stacks in the photo. They were done by some very talented ladies. These are 0402's by the way...

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