Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

SMTnet
»
Electronics Forum
»
Stencils

Stencils

Subscribe to Thread

Hello, I am new to the SMT world so i am still learning. I ... - Aug 08, 2023 by GrayUMM

You can use a stepper stencil but you can also try print out... - Aug 09, 2023 by serge_pirog

Consider opening the stencil aperture to increase the amount... - Aug 09, 2023 by davef

The first thing I do when looking at a part relative to sten... - Aug 09, 2023 by SMTA-64386426 SMTA

Hello, I have requested an overprint to our PCB Designer, we... - Aug 10, 2023 by GrayUMM

you can put BEFORE the connector so-called preforms - if the... - Aug 11, 2023 by Michał

Usually, for big connectors like this, you can use a red smt... - Aug 13, 2023 by Kirillka

This one picture would help us so much to assess. Step stenc... - Aug 15, 2023 by Evtimov

Evtimov, here is a picture of what we are seeing. After eval... - Aug 22, 2023 by GrayUMM

I would start with the following possibilities and solutions... - Aug 31, 2023 by Auriga2001

GrayUMM

#89842

Stencils | 8 August, 2023

Hello,

I am new to the SMT world so i am still learning. I was previously a Controls Eng so there is alot that i do not know or just haven't seen yet. I come today with a question i was hoping to ask someone with more experience.

We have a Connector, MOLEX 430450419, that isn't receiving enough solder paste and failing for connection when it reaches our test department. I've tried adjusting the settings on the AOI to look for insufficient solder, but the problem is that the solder is there it's just not getting enough onto the lead to make a good connection; the coplanarity doesn't seem to be an issue.

The Stencil size we are using is 4mil/101.6um

Does anyone have any ideas? Would a stepper stencil be something i could suggest to our design Engineers?

Thanks in advance.

reply »

serge_pirog

#89843

Stencils | 9 August, 2023

You can use a stepper stencil but you can also try print outside of contact pads. Design an aperture that extends beyond pads and paste will be on the soldermask. In the oven it will return to leads. If you need help with development, please contact.

reply »

davef

#89847

Stencils | 9 August, 2023

Consider opening the stencil aperture to increase the amount of solder available to the connector leads.

reply »

SMTA-64386426

#89848

Stencils | 9 August, 2023

The first thing I do when looking at a part relative to stencil design, is determine the coplanarity per the data sheet. Ideally your stencil thickness should be equal to, or if needed, greater than the coplanarity. You want the solder paste to come into contact with the lead prior to reflow, so the flux has a chance to do its thing on the device lead. So as this part has a 6 mil coplanarity, and your stencil is 4 mils, you are likely to have insufficient solder or even non wetting. A step up can work, or if the stencil thickness was already good, an over print works good. You might want to do both. I typically over print this style of connector in both length (heel and toe) and width. The pitch is so large, you will not have an issue with shorts. If you do go with a step stencil, you need to evaluate step spacing, adjacent components affected due to blade deflection, and may even need change your print parameters.

This message was posted via the Electronics Forum @ SMTA SMTA

reply »

GrayUMM

#89855

Stencils | 10 August, 2023

Hello, I have requested an overprint to our PCB Designer, we are already overprinting for some of our pin in paste connectors so this shouldn't be a big deal. Will reply back with results. Thank you everyone.

reply »

Michał

#89859

Stencils | 11 August, 2023

you can put BEFORE the connector so-called preforms - if the connector falls over, enlarge the pads under the connector and place the preforms next to the leads

reply »

Kirillka

#89868

Stencils | 13 August, 2023

Usually, for big connectors like this, you can use a red smt glue under the connector with a dispenser. If its not possible, you can use the same red glue and put a small dot on the side of the connector after reflow, and heat it a bit with blower, 150c should be enough for couple seconds, until it changes color.

reply »

Evtimov

#89885

Stencils | 15 August, 2023

This one picture would help us so much to assess. Step stencil to 6mil for the connector area.If this doe not resolve it, start thinking about part contamination, insufficient heat in reflow profile and a few other

reply »

GrayUMM

#89906

Stencils | 22 August, 2023

Evtimov, here is a picture of what we are seeing. After evaluating with the IPC-A-610 book it looks like we are getting an insufficient Heel Fillet Height. I will add a picture of an example. UPDATE: i cannot figure out how to add a picture to this message

reply »

Auriga2001

#89934

Stencils | 31 August, 2023

I would start with the following possibilities and solutions:

Add extra solder to the pads with a Camalot dispenser; or preformed solder slugs placed as an additional component if there is enough extra pad to attach it without interfering with component placement.

Bump up the stencil thickness; at least around the connector, using a step. Or make the whole stencil thicker as long as it doesn't overload solder on smaller pads.

It may be possible that the component has some contamination that is preventing a good flow up the leads.

Attachments: