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Solder cover

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#61285

Solder cover | 3 March, 2010

Hello Sir. Our customer asked me why the solder did not cover the surface of the potocopuler lead. There are 2 ea of photocopuler on pcb and the leads are totally 8ea. But only one is showing this problem. When i reviewed the reflow profile, there was no problem and when i compared it with other leads, the solder amount and solder fillet was not bad. And i also inspected the lead but the lead was not contaminated. Our customer believe that this can affect the adhesion in the future. Please the attached picture and advice how can i explain to our customer.

Thanks. Ju-young.Jeong

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#61286

Solder cover | 3 March, 2010

The picture shows that the heel of the device lead is not on the pad. Either bad placement or wrong pad dimensions. I imagine most customers would reject this joint as only a small part of the lead is actually in the solder. With no heel fillet the joint will be much weaker then with a well formed heel fillet. Compare your image with the ones for gull wing devices in the Surface Mount Assembly section of IPC610 spec. You can't have a heel fillet if the heel isn't on the pad...so its probably a reject for class 1.

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#61288

Solder cover | 3 March, 2010

I agree with Graham. What isn't clear is the cause; Was the PCB layout not correct for the device, or was the component not placed properly.

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#61292

Solder cover | 3 March, 2010

Hello Graham Copper. Thanks for yr comment. I will review the pad size and component placement with our engineer. It looks that the placement of lead is wrong. But what i want to hear from you is about solder lump on the right.As you can see, the solder did not spread. Our customer thinks that this is caused by the insufficient reflow profile. But other leads were covered with solder. Our engineer reviewed the reflow profile and said this was not related to reflow conditions. Please tell me your idea. Thanks. Ju-young.Jeong

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#61294

Solder cover | 3 March, 2010

If your "engineer reviewed the reflow profile and said this was not related to reflow conditions," then what does he think it's related to?

We think that a increased effort to improve the thermal recipe to solder this part is required, because: * Solder on this pad has poor wetting. * There appears to be a glob of solder on the upper part of the component lead that doesn't appear to be smoothly connected to other soldered areas on the lead. * Other parts soldered acceptably.

How does the temperature through the reflow cycle on this lead compare with other leads that that have acceptable appearance?

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#61303

Solder cover | 5 March, 2010

Hi, Do you have a picture on one of these leads where the solder has covered the lead ? As this is a gull wing device I wouldn't expect solder to cover it. I expect to see a toe fillet / wetting around the sides of the lead and a heel fillet. If your customer is expecting to see solder cover the top of the lead then he has false expectations (see IPC 610). This does sometimes happen however depending on a number of things like solder volume / metalisation on leads. If you can attach an example of what the other leads look like (covered with solder) then I may be able to offer some ideas. Thanks

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#61304

Solder cover | 5 March, 2010

Ya, that could be happened bcoz of reflow profile.I think, in this case, each lead got the different temperature during the reflow process. If the solder had melted properly,the hot lead would have attracted the solder to cover itself.

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#61305

Solder cover | 5 March, 2010

Are both photocouplers exactly the same ? More importantly, do they have exactly the same metalisation on their legs ? I have experience where same relay devices have different leg metalisations (one was matte tin / one was gold over platinum over nickel ) The difference in joint appearance caused confusion with the customer.

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#61311

Solder cover | 5 March, 2010

Hello Guys. Many thanks for your interest in this matter. I believe we can solver this. The affected part is Photo coupler and has the same metallization. FYI, i attached another picture. You can compare the solder fillet of leads. The affected position and number of lead very. It is not the same position .It makes us be confused.How do you think about this? Thanks Ju-young.Jeong

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#61314

Solder cover | 6 March, 2010

Unfortunately, what you are calling a good fillet is not a good fillet. Solder on the top of the IC lead does not help to make a good connection. The most important fillet is the one located at the heel (think of the IC lead where it meets the PCB as a foot). This is also the hardest to see, except for the corner pins. From the images you've attached I can see that the pad layout is not appropriate because it does not allow for a fillet to form at the pins' heel. Here is an image (from IPC-A-610D) of a good fillet.

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#61317

Solder cover | 8 March, 2010

Hi, I fully agree with isd.jww. The difference in the solder joint appearance of the 2 joints highlighted could be down to a few reasons...reflow profile (I know you've checked, but have you stuck a thermocouple on this actual joint ? ), contamination on the device leg (it may not be visible), and maybe solder paste performance. Anyway, the pcb pad layout needs rectifying because at the moment all these joints are a defect as per IPC 610, and hence they cannot be considered reliable solder joints. Admittedly one may be more reliable then the other but because both are missing the heel fillet they will be significantly weaker then a 'target' solder joint. I hope this pcb isn't in any electronics I buy !

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#61845

Solder cover | 17 May, 2010

IPC also states that side overhang on a gull wing of 50% is acceptable for Class 2. Does anyone know if that interprets to only one side having a fillet? Also with toe overhang acceptable, there need not be a toe fillet.

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