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Mix Technology Board Processes

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Theresa Spear

#49210

Mix Technology Board Processes | 20 April, 2007

Instead of using adhesives to glue the back side SMD components and wave soldering them together with the through hole components, our manufacturing engineers choose to process the back side components through reflow oven without adhesives and process the topside components through reflow oven. After through hole components are inserted into the panels, the panel utilizes a wave solder pallet to protect the SMD components that are located at the back side of the panels when going through the wave soldering bath. I thought that the process is very efficient. However, the no clean flux started to build up at the opening of the wave pallets. One of the production runs had some leads not being soldered. Some people started to question the process. Can some one help me to do a comparison of this method vs using adhesive to clue the back side components? Are both processes widely utilized in the industry? What are known issues to either of the processes? Thank you for your help.

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#49227

Mix Technology Board Processes | 23 April, 2007

Hi T,

Gluing parts to the back side for wave solder is a widely used process. Running waves pallets is probably the last way I would want to run a wave. There are just so many things that have to be done to assure good quality first time pass, that could have been avoided if some up front "designing" was performed. That said, there may be a reason for your pallets. Are the parts just R�s and C�s or are there ICs on the back side? If all you have are Rs and Cs, they have to be in the proper direction for wave or you may get solder shorts and/or unacceptable solder joints. This extra bit of info is really needed to help find alternatives for you.

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#49229

Mix Technology Board Processes | 23 April, 2007

Glue application is widely used in my country.However, some companies want to save cost and remove the glue application. We are also using fixture to cover some components. It has no problem. Please try cleaning your fixture by alcohol or water.Brush it so that it will remove some flux.

issues of both process? 1. if your end product is used for heavy vibration application like car stereo, car parts etc. you must put glue or else your customer will make non glue a big issue. 2. If you want cost down remove the glue. 3.If you want to lessen your problem on the through hole buy selective soldering like K.I.S.S. from ACE. It is cheaper than other brands. if you like to know more please contact me grayman@ispx.com.ph

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#49231

Mix Technology Board Processes | 23 April, 2007

Wow, you're using the Surface Mount Adhesive for mechanical vibration? I've never heard of SMT adhesive being used for things other than holding the components in place before wave solder. Does it work for mechanical purposes?

Glue/Wave is a process that has been around for ages, but again, it depends on the board technology that your company uses. Typically, if you have bottom-side actives and lots of assemblies that have things smaller than 0805, glue/wave is NOT the way to go, and it will always yield worse than reflow/reflow. Also glue/wave adds cost if it's being dispensed instead of printed. But..if your PCBA technology is suitable for glue/wave, then that would be the way to go. If not, there's lots of pallet manufacturers out there who can even make pallets for difficult designs, like SMT too close to Through-Hole. The drawback of pallets, obviously, is storage, and obsolesence due to design changes.

If your through-hole componentry is minimal, the way to go would be selective soldering, just as Grayman suggests. Again, it'd depend on what your products' takt time requirements are (selective robot soldering is always slower).

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#49232

Mix Technology Board Processes | 23 April, 2007

We agree with Grayman. You should clean your fixtures. If you apply [leave] low residue flux in amounts greater than the supplier recommendation, the remaining residue can cause damgerous corrosion. Certainly it is then no longer low residue.

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#49241

Mix Technology Board Processes | 23 April, 2007

We have eliminated the adhesive process as much as possible. We do paste in hole where possible and selective solder the remaining components or hand solder them. We looked at this a number of ways and determined the selective soldering and hand soldering was better than using the adhesive and wave soldering. You may want to look at your products from this standpoint if you are an OEM and not a EMS provider.

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Theresa Spear

#49247

Mix Technology Board Processes | 23 April, 2007

Thank you all for your feedback. Our backside are 99.9% with passive components. However, we do have a lot of through hole components on boards. To go totally selective soldering the equipment can be quite expensive. Most of the time, we left the components that are closed to the surfacemount parts out during wave, then manual solder them post wave. We will certainly play with reducing the flux and clean the pallets.

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Hussman

#49258

Mix Technology Board Processes | 24 April, 2007

Why leave them out? Solder shorts?

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#49348

Mix Technology Board Processes | 26 April, 2007

I am guessing Theresa is saying when that some SMT parts are soldered (not glued) very close to some PTH parts. So close that they can't effectively mask the SMT parts and have an opening for the PTH part.

At the company where I work, we've been trying to eliminate SMT glue/wave as much as possible. We've found we have better yields with reflow solder on passives then with wave.

We still have many PTH parts on our assemblies, so we use custom wave carriers for just about every assembly.

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#49361

Mix Technology Board Processes | 27 April, 2007

There are several pallet manufacturers, Ascentec Engineering, Pentagon EMS, and S&P Engineering - to name a few - that make titanium inserts for wave pallets.

These inserts (inserted into your delmat or CDM material) will act as your pockets to mask neighboring SMT devices (as close as 0.010") from your throughole. They're made of Titanium because you can machine these at these small wall thicknesses.

They work well in most cases...some drawbacks are - you need to get the chamfer angles just right - especially on tightly pitched connectors, or you'll solder short. Also, you really need to pump solder in there, because a minimum 10mm pallet is needed for these inserts. Lots of cleaning required, and they're pricey, but it's still better than hand-soldering.

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