Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Rob Palson

#12166

Intrusive soldering | 22 March, 1999

Are there many of you who are soldering through hole parts in your surface mount reflow oven? How repeatable is the process? Do you need to touch up a lot after reflow? We don't do long runs maybe 200, 300 boards max. Can you just screen print the paste that you need for the through hole parts? Any input would be appreciated. Thank you.

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Bob Willis

#12167

Re: Intrusive soldering | 23 March, 1999

| Are there many of you who are soldering through hole parts in your surface mount reflow oven? How repeatable is the process? Do you need to touch up a lot after reflow? We don't do long runs maybe 200, 300 boards max. Can you just screen print the paste that you need for the through hole parts? Any input would be appreciated. Thank you. | Yes its a simple process with screen printing paste in and over the through hole parts, insertion of the parts and then reflow. The SMTnet book store has my video tape, CD ROM on sale.

SMTA has my report on the subject which is sold with all the money going to the Charles Hutchins Charity fund for students in the USA. Hope these help you out.

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Scott Davies

#12168

Re: Intrusive soldering | 23 March, 1999

Rob,

We are also using intrusive reflow to simultaneously process SMT and Thru-hole components. Our arrangement goes as follows:

- Screen print solder paste to the single sided PCB using 0.008" laser cut stencil. - Apply adhesive dots to selected components. - Place SMT components (1206, 0805, MELF and MiniMELF, SOIC). - Invert the board. - Hand load through hole components. - Reflow.

The adhesive dots are required to prevent certain components, such as MELF diodes and the larger SOICs, from falling off the board as it passes through the oven. We have spent a lot of time experimenting with reflow profiles to perfect this. Another common problem early on was tombstoning, but by adjusting the volume of paste printed and the reflow profile we have been able to control this.

We have found the soldering of the thru-hole parts to be generally successful, although not 100% reliable; we still have to touch up joints post-process. However, much of this could be improved by reviewing our board design; our hole to lead ratios are not really ideal for intrusive reflow. In addition, certain thru-hole components (eg. electrolytic capacitors) can suffer damage in the heat of the reflow oven required to give good soldering.

We are still very much in the middle of a learning process ourselves at the moment. Nevertheless, intrusive reflow appears to be a worthwhile process for certain applications, and it's certainly worth putting in the time and effort to give it a try.

Best Regards Scott Davies

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#12169

Re: Intrusive soldering | 23 March, 1999

| Are there many of you who are soldering through hole parts in your surface mount reflow oven? How repeatable is the process? Do you need to touch up a lot after reflow? We don't do long runs maybe 200, 300 boards max. Can you just screen print the paste that you need for the through hole parts? Any input would be appreciated. Thank you. |

Rob,

An excellent DOE on the topic was presented at Nepcon West by Kantesh Doss of Siemens in Johnson City, Tennessee. He performed a massive experiment with lead to hole ratios, stencil thicknesses, aperture sizes, etc. All the data is contained within the report, as are all the results and recommendations.

If you can't get a copy of it, let me know and I'll email or fax the paper from my proceedings disk.

Chrys

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Chris G.

#12170

Re: Intrusive soldering | 23 March, 1999

| Are there many of you who are soldering through hole parts in your surface mount reflow oven? How repeatable is the process? Do you need to touch up a lot after reflow? We don't do long runs maybe 200, 300 boards max. Can you just screen print the paste that you need for the through hole parts? Any input would be appreciated. Thank you. |

Rob,

As long as components can take the heat you should just give it a try. I have not done any fine pitch parts but have done lots of connectors, ceramic caps, and pins this way. Largest number of pins I have done on one single PCB was about 70 pins on about .100" spacing. Was not difficult to accomplish in our case. The process we used was:

Used a .010" step .006" stencil. Provided PCB is designed to segregate the through hole components you can use a stepped stencil.

Overprinted water soluable solder paste outside annular ring. This did not cause excess solder balls. Although we use nitrogen in oven. Have done with NC solder too.

Inserted pressfit square pins and through hole components. Pressfit pins reduced area left in through hole for solder. This probably helped us.

Reflowed in IR oven inerted with nitrogen. Have done in air as well. Very few solderballs from overprint when air was used. No solderballs when nitrogen was used.

Rarely ever had to rework using this process. Trick is to get stencil designed properly to put down enough paste and to design PCB through holes for optimum solder fillets with available solder paste. Almost always had solder fillets on both sides of inserted through hole components. Inspected to IPC class 3 and always passed fillet requirements and barrel fill. No reliability issues at all.

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Bob Willis

#12171

Re: Intrusive soldering | 25 March, 1999

| Rob, | | We are also using intrusive reflow to simultaneously process SMT and Thru-hole components. Our arrangement goes as follows: | | - Screen print solder paste to the single sided PCB using 0.008" laser cut stencil. | - Apply adhesive dots to selected components. | - Place SMT components (1206, 0805, MELF and MiniMELF, SOIC). | - Invert the board. | - Hand load through hole components. | - Reflow. | | The adhesive dots are required to prevent certain components, such as MELF diodes and the larger SOICs, from falling off the board as it passes through the oven. We have spent a lot of time experimenting with reflow profiles to perfect this. Another common problem early on was tombstoning, but by adjusting the volume of paste printed and the reflow profile we have been able to control this. | | We have found the soldering of the thru-hole parts to be generally successful, although not 100% reliable; we still have to touch up joints post-process. However, much of this could be improved by reviewing our board design; our hole to lead ratios are not really ideal for intrusive reflow. In addition, certain thru-hole components (eg. electrolytic capacitors) can suffer damage in the heat of the reflow oven required to give good soldering. | | We are still very much in the middle of a learning process ourselves at the moment. Nevertheless, intrusive reflow appears to be a worthwhile process for certain applications, and it's certainly worth putting in the time and effort to give it a try. | | Best Regards | Scott Davies | Nice one Scott, if any one did not read your note in detail they would have missed the fact that you are running the SDSRS Process. Similtanous Double Sided Reflow Soldering, I just published a report in the USA cover this process with the SMTA if you want to check with them. The report is for the Charles Hutchins Charity putting students through college.

Keep up the good work.

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