Wave Soldering Active Components

Hi Folks, This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. Thanks, John

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| Hi Folks, | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | Thanks, | John | John,

You are in such a wonderful position, as in how wonderful my life (and those of many others) once was. We put everyting on both sides except through hole devices. Maybe we do that too, I can't remember. Besides, if your arent't doing it today - you will be tomorrow.

All the folks contributing to this forum have told some awesome tails of do or die. The platter is yours from which to choose. It's a matter of when sir, how much sir, and what's it worth to you - sir. How, who, or why (until DFM is realized as an helpful addition to process control and relative cost) is never an issue when the foregoing is answered to you and your customer's satisfaction.

Earl Moon

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| | Hi Folks, | | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | | Thanks, | | John | | John,

You can go ahead with SOT23 in case you have dual wave option in your wave soldering machine. You will have to use both, the chip wave as well as the main wave to get good results with SOT23But in case you don't have chip wave option then you must not use SOT23 on the bottom side. For details you can contact mw on e-mail.

Regards Vinesh Gandhi

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John,

SOT 23's on the bottom side is no real problem...as long as you get the orientaion to the wave right and you remember to increase the pad sizees to allow the solder to get to the pads. Soldering with only one wave would be trick as Vinesh suggest's but it can and has been done with pretty good consistant resluts....

enjoy this cos from here on it ...it get's harder and much more fun

John W

| | | Hi Folks, | | | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | | | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | | | Thanks, | | | John | | | | John, | | You can go ahead with SOT23 in case you have dual wave option in your wave soldering machine. You will have to use both, the chip wave as well as the main wave to get good results with SOT23But in case you don't have chip wave option then you must not use SOT23 on the bottom side. For details you can contact mw on e-mail. | | Regards | Vinesh Gandhi |

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Thanks guys, since I have no control as to who makes the board (probably the lowest bidder), I guess I'll keep the SOT's on top. Thanks for your help, John

| John, | | SOT 23's on the bottom side is no real problem...as long as you get the orientaion to the wave right and you remember to increase the pad sizees to allow the solder to get to the pads. | Soldering with only one wave would be trick as Vinesh suggest's but it can and has been done with pretty good consistant resluts.... | | enjoy this cos from here on it ...it get's harder and much more fun | | | John W | | | | | Hi Folks, | | | | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | | | | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | | | | Thanks, | | | | John | | | | | | John, | | | | You can go ahead with SOT23 in case you have dual wave option in your wave soldering machine. You will have to use both, the chip wave as well as the main wave to get good results with SOT23But in case you don't have chip wave option then you must not use SOT23 on the bottom side. For details you can contact mw on e-mail. | | | | Regards | | Vinesh Gandhi | | | |

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| Hi Folks, | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | Thanks, | John | You can wave solder SOIC, SOT23 and any chip components on the base of the board. You can also wave solder QFP down to 0.032" pitch with very good yields.

Remember that as the complexity of the boards and pitch changes so the yields will be effected if the process is not in control. Another key aspect is confirming that all you components are compatible with the process temperatures of the wave 245-255C max. Use the IPC component compatability spec for ref.

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| Hi Folks, | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | Thanks, | John | John,

Like Earl said, it's a great world you live in if you have the option of keeping SOT's on top. But if you can't, a few tricks in the design might help you get an assembly that is robust enough to survive even the lowest of low bidders for the assy:

- Orient the pads parallel to the wave to prevent component body shadowing. - Leave a good web of soldermask between the two pads on the same side of the device to prevent bridging (at least 25 mil). - Put them in the center of the board. Wave solder machines running without good control can have shorter contact lengths at the edges of the wave (bad parallelism in the setup - a commmon problem). You're assured better dwell time in the wave if your parts are in the middle.

Additionally ,as for beefing the design up for the lowest bidder, you may want to stick with 1206's if possible. Low bidders don't always have great glue dispensing processes. You need a smaller dot for an 0805 than you do for a 1206. Not only can they be more diifcult to make, but the smaller contact area means less adhesion. Lots of 0805's have taller profiles than their 1206 counterparts, which gives them a higher center of gravity and makes it easier for the wave to knock them off (especially if there's less glue holding them on).

Cheers,

Chrys

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| Hi Folks, | This is my first surface mount board, so I asked our assembly house for some tips. They said only passives on the bottom side-preferably no smaller than 0805, 0603 only if I have to. I would think that an SOT-23 would be OK on the bottom. | What do you folks normally put on the bottom? I would like to stay away from tooled fixtures if possible. | Thanks, | John | John,

Like Earl mentioned, we load all kinds of smd on both sides, including monster qfp's...however, we do not use the wave to acheive the solder joints, rather stencil paste reflow. Then you just mask off the qfp leads (for example), and let the wave do its magic to the TH parts. I wasn't sure from your message if that was your question, but just in case it was.....

Regards, Marc

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