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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Tombstone components issue after reflow?

Views: 6052

#78673

Tombstone components issue after reflow? | 11 August, 2017

Anyone who knows how to prevent such flaw?

Tombstones are those lifted components from one sides. This results in costly and time-consuming amounts of touch-up and re-work after the assembly is completed. For the customers, this extra work translates into delayed delivery shipment, cost increases, and considerable (but unnecessary) stress being placed on the board's existing components.

Attachments:

reply »

#78676

Tombstone components issue after reflow? | 12 August, 2017

There is no solution in above case, this is caused by the PCB design. There are no thermals on the pads connected to the copper poured area. So the other pad reflow first and lift the component.

reply »

#78682

Tombstone components issue after reflow? | 13 August, 2017

> Anyone who knows how to prevent such > flaw? > > Tombstones are those lifted components > from one sides. This results in costly and > time-consuming amounts of touch-up and re-work > after the assembly is completed. For the > customers, this extra work translates into > delayed delivery shipment, cost increases, and > considerable (but unnecessary) stress being > placed on the board's existing components.

This flaw could be due to inaccurate stencil design, among other factors. The assembly process can incur adverse effects when the stencil is not accurately designed. There can be such flaws as a number of tombstones and bridging when an incorrect stencil is run through the pick-and-place and reflow process.you share the screenshots of GTL with GTO and GBL with GBO for a further check?

reply »

#78684

Tombstone components issue after reflow? | 14 August, 2017

> There is no solution in above case, this is > caused by the PCB design. There are no > thermals on the pads connected to the copper > poured area. So the other pad reflow first and > lift the component.

Yes, this. You could try playing with the profile shape and that might reduce the problem, you could even try gluing the caps but until this board design is changed this problem will never go away. For the most part I would say that if a change of stencil design helps with an issue like this, the underlying design was still flawed.

reply »

#78689

Tombstone components issue after reflow? | 14 August, 2017

Any of the comments so far could be valid. To add my opinion, it looks like the pad size is too large. A smaller volume of solder will pull less than a larger volume. If you can't change the pad sizes, then the next thing to try is to get another stencil but modify the apertures so that only half the pad receives paste. I would print paste on the inner halves of the pad so that the part is set in the paste and let the outer halves unpasted.

This document might help: https://www.smtnet.com/library/files/upload/EFD-Tombstone-Troubleshooting.pdf

reply »

#78690

Tombstone components issue after reflow? | 14 August, 2017

Here is some food for thought. Try to answer these questions yourself and I am sure you will see huge improvement.

Reasons:

- Bad PCB design - Plating-uneven HASL cause more than OSP Au/Ni or Silver - Poor paste and print quality - uneven paste can cause it - Paste type - Type 4 is most resistant to Tombstone - Stencil - home plate apertures help reducing tombstone. Also decrease the volume of metal overall. - Incorrect placement of parts - parts should be centered to apertures. - Placement pressure - Paste composition and paste storage - Reflow profile

If you don't have control over design, next thing to do is print much less paste(homeplate apertures is better).

reply »

#78691

Tombstone components issue after reflow? | 14 August, 2017

God I hate the formatting of my post!

reply »

#78712

Tombstone components issue after reflow? | 16 August, 2017

Not enough solderpaste. Uneven solderpaste volume on pads. Bad quality of caps ( Metal ends), try new cap manufacturer, sound weird, huh!! but that happened to me. Good luck.

reply »

#78716

Tombstone components issue after reflow? | yesterday at 12:18 PM

I do not see anything obvious that would cause a thermal mis match.

Regarding reflow profiles reducing tombstoning, Unless there is something wrong with your paste or you are running smaller than 0402's, I have NEVER seen a reflow profile reduce tombstones unless there is something grossly out of whack with it.

As you can see from the responses there are many factors to consider.

The most common cause is incorrect land design and component plating issues.

reply »

#78717

Tombstone components issue after reflow? | yesterday at 12:59 PM

There is DFM Design for Manufacturing, but now I see DFF Design for Failure.

Start over.

reply »

#78721

Tombstone components issue after reflow? | today at 03:46 AM

The first reply from Tsvetan Usunov already answered your question - there are no thermals for one side of the chips.

You can try to reduce the phenomenon by using different solder pastes, tuning your soldering profile or even switching to different Mfr, BUT here it's obvious that the design is faulty. You will not be able to solve it for good without design's correction. Of course you can always glue the chips but that's a bit nonsense..

reply »

Reflow Oven

reflow oven profiler