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Solder Wicking on CBGA?

Karlin

#14595

Solder Wicking on CBGA? | 23 August, 1998

Hi, Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. Your advice is appreciated.

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JUSTIN MEDERNACH

#14596

Re: Solder Wicking on CBGA? | 24 August, 1998

| Hi, | Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. | We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. | Your advice is appreciated. Karlin, I suspect you are using a .006" thick stencil or less. CBGA's demonstrate the phenomenon that you are referring to. Sometimes it is necessary to go to an .008" thick stencil and then step it down in areas where there are fine pitch architectures. Regards, Justin Medernach

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Karlin

#14597

Re: Solder Wicking on CBGA? | 24 August, 1998

| | Hi, | | Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. | | We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. | | Your advice is appreciated. | Karlin, | I suspect you are using a .006" thick stencil or less. CBGA's demonstrate the phenomenon that you are referring to. Sometimes it is necessary to go to an .008" thick stencil and then step it down in areas where there are fine pitch architectures. | Regards, | Justin Medernach Yes, I am using 6 mils stencil! Just need to clarify, It is advisible to have 8 mils stencil because of paste height not enough or solder paste deposition volume is not enough? My average solder paste height after printing is about 7.9 mils. regard, Karlin

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Justin Medernach

#14598

Re: Solder Wicking on CBGA? | 25 August, 1998

| | | Hi, | | | Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. | | | We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. | | | Your advice is appreciated. | | Karlin, | | I suspect you are using a .006" thick stencil or less. CBGA's demonstrate the phenomenon that you are referring to. Sometimes it is necessary to go to an .008" thick stencil and then step it down in areas where there are fine pitch architectures. | | Regards, | | Justin Medernach | Yes, I am using 6 mils stencil! Just need to clarify, It is advisible to have 8 mils stencil because of paste height not enough or solder paste deposition volume is not enough? My average solder paste height after printing is about 7.9 mils. | regard, | Karlin Karlin, 7.9 mils seems a bit excessive for a .006" foil. Is that height obtained purely after printing or do you take a pre-print HASL height and then a post print paste height and take the difference between the two? Yes, you need the volume but I don't recommend going larger than 34 mils in diameter. Re-verify your paste height by using the aforementioned method and I think you'll find that you are applying less paste than you thought. Also, check the calibration of your paste height measurement instrument by measuring the hieght of an 0603 passive component with a set of calipers and check that result against the height obtained by the measurement unit. Hope some of this helped. Regards, Justin Medernach Flextronics International

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Karlin

#14599

What cause Solder Wicking ? | 25 August, 1998

| | | | Hi, | | | | Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. | | | | We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. | | | | Your advice is appreciated. | | | Karlin, | | | I suspect you are using a .006" thick stencil or less. CBGA's demonstrate the phenomenon that you are referring to. Sometimes it is necessary to go to an .008" thick stencil and then step it down in areas where there are fine pitch architectures. | | | Regards, | | | Justin Medernach | | Yes, I am using 6 mils stencil! Just need to clarify, It is advisible to have 8 mils stencil because of paste height not enough or solder paste deposition volume is not enough? My average solder paste height after printing is about 7.9 mils. | | regard, | | Karlin | Karlin, | 7.9 mils seems a bit excessive for a .006" foil. Is that height obtained purely after printing or do you take a pre-print HASL height and then a post print paste height and take the difference between the two? Yes, you need the volume but I don't recommend going larger than 34 mils in diameter. Re-verify your paste height by using the aforementioned method and I think you'll find that you are applying less paste than you thought. Also, check the calibration of your paste height measurement instrument by measuring the hieght of an 0603 passive component with a set of calipers and check that result against the height obtained by the measurement unit. Hope some of this helped. | Regards, | Justin Medernach | Flextronics International Hi Justin, Thank a lot! Will tryout using new stencil. By the way what is the root cause of solder wicking? You see, I have two Ceremic BGA that mounted on the board, one with smaller size 21 x 21 mm has never give us this problem since day one production until now. The other with 21 x 25 mm consistantly give us the solder wicking problem. Any comment? Thank in advance, rgs, Karlin

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Justin Medernach

#14600

Re: What cause Solder Wicking ? | 27 August, 1998

| | | | | Hi, | | | | | Does anyone has experiences in reflowing Ceramic BGA and found solder wicking ? Solder wicking has the syndrome that solder being wick from the pad and ended up in the leads. | | | | | We have rule out the possibility of not printing any solder paste there because we perform 100% inspection after solder printing.The stencil hole opening is 34 mils in diameter. | | | | | Your advice is appreciated. | | | | Karlin, | | | | I suspect you are using a .006" thick stencil or less. CBGA's demonstrate the phenomenon that you are referring to. Sometimes it is necessary to go to an .008" thick stencil and then step it down in areas where there are fine pitch architectures. | | | | Regards, | | | | Justin Medernach | | | Yes, I am using 6 mils stencil! Just need to clarify, It is advisible to have 8 mils stencil because of paste height not enough or solder paste deposition volume is not enough? My average solder paste height after printing is about 7.9 mils. | | | regard, | | | Karlin | | Karlin, | | 7.9 mils seems a bit excessive for a .006" foil. Is that height obtained purely after printing or do you take a pre-print HASL height and then a post print paste height and take the difference between the two? Yes, you need the volume but I don't recommend going larger than 34 mils in diameter. Re-verify your paste height by using the aforementioned method and I think you'll find that you are applying less paste than you thought. Also, check the calibration of your paste height measurement instrument by measuring the hieght of an 0603 passive component with a set of calipers and check that result against the height obtained by the measurement unit. Hope some of this helped. | | Regards, | | Justin Medernach | | Flextronics International | Hi Justin, | Thank a lot! Will tryout using new stencil. By the way what is the root cause of solder wicking? You see, I have two Ceremic BGA that mounted on the board, one with smaller size 21 x 21 mm has never give us this problem since day one production until now. The other with 21 x 25 mm consistantly give us the solder wicking problem. Any comment? | Thank in advance, | rgs, | Karlin Karlin, Are the spheres the same diameter on both devices? This phenomenon is pretty odd if they are and I honestly don't have an explanation unless there are differences in the aperture or pad sizes. As for the "why"; The CBGA uses hi-temp solder spheres. Solder paste, when eutectic and fluxed, likes to climb onto metal. Perhaps your components are more solderable than your boards. Look at your board cleanliness or for oxidized pads. If this were the case the solder would tend to flow to the most solderable surface or the spheres. rgs, Justin Medernach

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