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BGA shorts

BGA shorts

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Fellas, Here's the deal. We're getting shorts on a limited... - Feb 14, 2001 by

Do you have a stencil wipe step after every six boards? If ... - Feb 14, 2001 by lileubie

I'm sorry, I should clarify. The average is one out of six ... - Feb 14, 2001 by

BGA Shorting 1 Damaged mask in between the BGA pad and vi... - Feb 14, 2001 by davef

This message has nothing to do with BGA short, but I spent 3... - Feb 15, 2001 by Mohammed Saad

Antonio, one possibility I have seen before on BGA ... - Feb 15, 2001 by

I assume Roland [er someone like that] explained on the Main... - Feb 15, 2001 by davef

Antonio

#5231

BGA shorts | 14 February, 2001

Fellas, Here's the deal. We're getting shorts on a limited number of boards under the BGAs; about 1 out of 6 boards. The thing is that these boards have about 10 BGAs on them. On the one out of six boards with shorts, the shorts are everywhere and usually on every BGA on that board. Then there's five boards with no shorts at all! All the boards are run at the same time, same people, same everything. What could cause massive amounts of shorts on just one board instead of repeating on all of them?

Thanks in advance... Antonio

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lileubie

#5232

BGA shorts | 14 February, 2001

Do you have a stencil wipe step after every six boards? If so, the wipe either automatic or manual needs to be optimized. Either less solvent or more time for the solvent to evaporate off.

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Antonio

#5234

BGA shorts | 14 February, 2001

I'm sorry, I should clarify. The average is one out of six boards. It's not consistant as to how many are good before a really bad one. Sometimes two in a row, sometimes ten. Right now we are wiping every 2 boards.

Antonio

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davef

#5237

BGA shorts | 14 February, 2001

BGA Shorting

1 Damaged mask in between the BGA pad and via on the substrate.

2 Poor print registration.

3 Poor via segregation from the pads? Are they tented or is there just a dam in between?

4 Review the profile. You can run into a number of problems in BGA rework, if the profile is incorrect.

5 An inert reflow atmosphere helps

6 Solder shorts: Moisture entrapment causes solder shorts 80% of the time. Cracks occur bottom side. Use acoustic microscope to find.

7 Warping BGA are the usual cause of shorts in the corners and are usually caused by the reflow profile. BGA have a natural tendency to warp due to CTE and package thermal mismatch as you have seen at rework.

8 However, if the BGA was reflowing fine, and all of a sudden, with the same reflow profile, it now warps in the corners; it is likely the fault of the component. If that is the case, you can usually isolate it to a specific date code. Most plastic BGA have their tops injection molded. The heat and pressure can leave residual stress in the component. This stress will relieve itself by warping the component during reflow. You can often times see warped packages prior to reflow as well.

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Mohammed Saad

#5239

No residue low tack adhesive film for registration | 15 February, 2001

This message has nothing to do with BGA short, but I spent 30 min trying to find out how to post a new message but I couldn't find it!!!

My question is:

Does any one know what is "No residue low tack adhesive film used for registration" is used for what registration and in what industry??

Thank you for your help

msaad

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CRAIGS

#5240

BGA shorts | 15 February, 2001

Antonio, one possibility I have seen before on BGA shorts was due to chain slippage on the reflow oven due to worn gearing, the slippage was not severe enough to move other SMT devices but was enough to disturb the molten solder under the BGA's causing shorts. This only occured on the board which was in the reflow zone, the slippage varied in time from between 1 minute and 5 minutes depending on how the gearing picked up the chain, which would tie in with the results you are seeing. If you have a new oven shouldn't be the issue but is one more area to look at.

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davef

#5244

No residue low tack adhesive film for registration | 15 February, 2001

I assume Roland [er someone like that] explained on the Main Conference also known as the Forum, the blue "New Thread" button near the middle of the page and 1 1/2" in from the right margin as the preferred way for posting a new thread. [Well, if they didn�t, there ya go!!]

If you get lost, select "SMTnet.com" on the left of the gray bar near the top of the page.

What do you mean when saying "No residue low tack adhesive film used for registration"?

Without waiting for your answer, two possibilities come to mind:

1 Before removing a BGA, we put Kapton tape along the edges of the device to aid in registering the replacement [when the rocket scientist designer doesn�t bother to give us some foil to help us out]. The punks!!! [An aside on Kapton tape, not all Kapton tapes are created equal. Source control yours, once you find one you like, to prevent your buyer from becoming a "hero" by finding a cheaper source.]

2 Before placing SMT components on a board, we run a first piece to check machine programming by placing components on the board, but use a "tape", rather than paste, to hold components in place during QC checking of component registration. In this, we are concerned about both low res and low ESD sensitivity tape.

Production Analysis 803 Forepeak Dr Forked River, NJ 08731 609.693.4885 http://www.lancesmalley.com

It�s nice that it�s reusable, but recognize that this stuff is not going to do anything good for ESD sensitive components. Forewarned is forearmed.

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