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Tantalum caps causing misaligned parts

mantis

#23870

Tantalum caps causing misaligned parts | 21 March, 2003

Hi all, I have a strange problem,while building a large 15x15inch 3.5mm thick Pcb.During topside reflow i am experiencing some misaligned parts and even bridging on a bga that are sitting very close to a D size tantalum cap.The strange thing is that if you change to a diffrent vendor the issue disappears, i have examined the data sheets for both parts and there is no physical diffrence.I have been up and down the line with a fine tooth comb and it is definetly being misaligned in the oven.Has anybody ever seen/heard or come across anything like/similar to this problem. Any insight would be much appreciated. Regards

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#23871

Tantalum caps causing misaligned parts | 21 March, 2003

Different vendor for: * Tants * BGA

BGA correct?

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mantis

#23873

Tantalum caps causing misaligned parts | 21 March, 2003

Sorry i didnt explain it vey well,the parts that are misaligned are always sitting next to these particular tanatlum capacitors.It affects 0805 parts and A tsop36 and can even cause a short on a bga right in the corner where the tant sits.If you change the vendor the issue goes away.So my question is what could be causing it and why does it disappear if you change vendors if the two parts have the same physical characteristics. it has me stumped ?????? any insights? regards

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#23875

Tantalum caps causing misaligned parts | 21 March, 2003

Change the vendor of what? The BGA, the Cap, the 0805?

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Jon Fox

#23876

Tantalum caps causing misaligned parts | 21 March, 2003

His subject line is "Tantalum caps causing misaligned parts". Come on guys, I think he answered the question already. Is there any via/traces that connects the pads of the TANT to the 0805 and the BGA. Your two parts may be physically the same, but what about electrically (Tol%, voltage, etc...) The one vendor's TANT could be acting as some type of heat sink, or (don't ask me how), be pushing heat away from the TANT. Do the two types of TANT have the same lead plating on the leads?

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#23877

Tantalum caps causing misaligned parts | 21 March, 2003

Could the case material or thickness of the Tantulums be different? Have you contacted the manufacturers to find out? A lot of times there is data that doesn't appear on the datasheets.

James

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mantis

#23878

Tantalum caps causing misaligned parts | 21 March, 2003

I have contacted both vendors with this issue and the both said they have never heard of such a problem and that they could offer no type of explanitation.The leads are 90 sn/10pb and 98sn/2pb respectivley. The parts are all connected to the vcc and gnd layers. Could there be some mad air vortices causing the parts to shift in the oven or maybe the tants are becoming magnetised....sorry sorry im going into science fiction here but its p****ing me off

some counselling would be really appreciated regards little green man

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Stephen

#23879

Tantalum caps causing misaligned parts | 21 March, 2003

I once worked for a new branch of a company. We had a board where one of two tants would shift in the oven. When I phoned up HQ because they had ran the board before as soon as I said the product name their guy said "C148 shifts in the oven" He knew what I was going to say before I did. They used a piece of paper to keep it straight, we used a drop of epoxy before placement. Neither solution can work for you. The strange thing is that cap was in two places on the board and only one did the oven dance. All I can suggest is profile with each part, and put a thermocouple at both ends. The tants must be thermally different. One either has a higher thermal capacity or a lower thermal resistance. Another thought, you are not using an IR oven are you? And are the Tants the same colour?

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#23897

Tantalum caps causing misaligned parts | 24 March, 2003

Hi mantis, this effect you are talking about is very interesting.I guess there is a difference in technology of both vendors.It;s obvious.But we should find the reason. One question and one simple sudgestion:What excatly is your oven? And have you passed the board in all possible directions.Try in all 4 directions and see the results.They should be different.I am very interested in examine that problem.If you solve it please inform us.

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Kelly

#23937

Tantalum caps causing misaligned parts | 27 March, 2003

Is one vendors 0805 thicker than the other? If the height of the parts are different, this could be part of the reason for the shift on only one 0805.

Good Luck! Kelly

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kenlchin

#23940

Tantalum caps causing misaligned parts | 27 March, 2003

Hi,mantis, I has experienced this case.when we run a model ,misalignment and tombstone of some 0805 resistors and 1206 caps always occured.we have taken many actions,such as adjusting reflow parameter&printing parameter,checking pcb and parts solderability,and changing these defective components.but these defects still exist.then we observed these parts and location.we found it is the same part near these defective parts.and it is TAN CAP.So we changed the vendor from kemit to AVL.then the problem disppeared.why do the tan cap affect the near parts? we think The TAN CAP is wet ,when reflow,outgasing occured,which lead to the near parts misaligned or tombstone.then we baked the TANT CAP before used,and the problem is resolved.now we request Kemit use vacuum-packed ,and it's ok.

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