We place Melf parts without a problem. When we start seeing Melf parts not straight on the pads it is has been for two reasons. The nozzle or the head that holds the nozzle has a reduced amount of vacuum because of dirt. We cleaned the head and nozzle and the pickups and placements went back to normal.
The second issue is conveyor alignment. The operators must open or close the conveyors between the machines for the width of the boards being processed. If they aren't perfectly aligned, usually it is the adjustable rail side, then the Melfs and tall can-type capacitors will shift when the board traveling from the machine at a good speed, hits the cornor of the entrance of one of the other conveyors. You will get a random result as the bow in the board will contact the belt differently and may feed straight or turn slightly just enough to cause a shift on these two part types. You may want to look at the speed the conveyors in the machine and external conveyors are are set to and see if the match or need to be slowed down.
Hope this experience helps.
-------------- Original message --------------
From: "Wilson, Bob" <[log in to unmask]>
> I agree too, but the part that made me help him out was that he said the
> customer wanted it.
>
> I try to point things out to customers and after frothing and foaming and
> fulminating for a bit, I mellow out and give them what they want.
>
> "Democracy is the theory that the common people know what they want, and deserve
> to get it good and hard."
> H. L. Mencken
>
> Bob Wilson
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Thursday, November 20, 2008 11:57 AM
> To: [log in to unmask]
> Subject: Re: [TN] MELF pad shape question
>
> I second Steve,
>
> U-shaped for MELF can cause the component to roll all over the place on the PCB,
> since they simply give less contact between the component and the part, so less
> tack.
>
> Regards,
>
> Ioan
>
> -----Message d'origine-----
> De : TechNet [mailto:[log in to unmask]] De la part de Steve Gregory
> Envoyé : 20 novembre 2008 14:53
> À : [log in to unmask]
> Objet : Re: [TN] MELF pad shape question
>
> Hi Carl & Ben,
>
> I've seen those "U" shaped pads for MELF's as well as just plain ol'
> square pads. Personally, I think what might have been a good idea at one
> time really isn't necessary for MELF's. The solder paste holds the part
> just fine. In fact, I've seen the "U" shaped pads cause the parts to
> skew sometimes during reflow. While maybe not a defect, it looks ugly.
>
> Am I the only who has seen that?
>
> Steve
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
> Sent: Thursday, November 20, 2008 9:26 AM
> To: [log in to unmask]
> Subject: Re: [TN] MELF pad shape question
>
> Carl,
>
> This notch is used to prevent edge overhang of the component. The pad
> shape helps keep the component centered on the pad, otherwise the wider
> middle of the component may overhang the pad edge even if the narrower
> bottom is on the pad and soldered.
>
> Ben
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
> Sent: Thursday, November 20, 2008 10:09 AM
> To: [log in to unmask]
> Subject: [TN] MELF pad shape question
>
> A customer is using MELF parts on an existing board and is asking us to
> add some more parts of a different size. The new parts are DL-35 and
> the manufacturers data sheet shows a rectangular pad as the recommended
> size. All of the MELF parts on their current board have small notches
> at the middle-inside of each pad like:
>
> ********** **********
> ********** **********
> ***** *****
> ********** **********
> ********** **********
>
> The customer is requesting that we make pads similar to pads on other
> parts, but properly sized for the DL-35 part.
>
> Questions:
> 1. Why would pads need to have this notch?
> 2. Where can I get recommendations on how to create a notched pad
>
> Thanks,
> Carl
>
>
>
>
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