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SMT electronics assembly manufacturing forum.

Help with resources for SMT assembly

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Help with resources for SMT assembly | 25 July, 2015

I am looking for information regarding setting up an SMT assembly line. I have recently purchased a stencil paste printer, pick and place, and reflow oven. The main information I need is the paste selection and best finish material on the PCBs. I will be wanting lead free, no clean solder and from what I have learned so far I need a paste with gelling agent and one that does not compose before 217 degrees C. But, when I browse for available paste, I cannot identify these attributes. Also, what PCB finish would work best with this paste and reflow process? Should I select tin, silver, gold immersion etc? Thanks in advance for you help Regards David

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Help with resources for SMT assembly | 26 July, 2015 this site has some pretty good general advice for the novice. I am in no way affiliated with it and I have no idea as to its eventual commerical aims (if any).

ENIG if your product can justify the cost is by far the best option for PCB finish. It is flat, clean and stores well.

Most paste manufacturers will happily send you a pot to try for free. That way you get to put the paste through your process with your products. Nobody else can really tell you what will work best for you.

There are several alloys out there for lead free process but by far the most common is SAC305. Most manufacturers will offer this in a no-clean variant. In the UK at least getting non no-clean SAC305 paste is actually often a special order requirement. I wouldn't concern yourself with looking for extreme detail on flux properties. If the paste uses the right alloy and has the cleaning poperties you require the flux will have the properties required because if it didn't it would not be fit for purpose.

Instead you should look at the properties that match how you use it. Storage, how long you can leave it on a stencil, how long you can leave it on PCB before reflow. How quickly you have to finish the pot once you have opened it. Plenty of pastes expire in 7 days or less once you break the seal.

As a small batch manufacturer we have specifially chosen a paste that once removed from cold storage (where it is happy for 6 months) can be kept at 30C for 30 days and remain perfectly useable. Henkel now make a paste called GC10 that goes even further with properties that allow you to treat paste in ways that would have half the engineers on here frothing at the mouth with apoplectic rage.

Suggestions on pastes to try depend on where you are. In the UK you can try Multicore (Henkel), BLT, Almit, DKL, Warton (By far the cheapest, but not as much information in their datasheets),Qualitek,KOKI & Cobar to name just a few. The manufacturer or representative will send you a sample in all cases. Several of them also have an engineer who will visit to give advice, point you to the correct paste, help with your profile (using their own equipment). I have no doubt the same is true in other territories.

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Help with resources for SMT assembly | 26 July, 2015

Thank you for your prompt response. The boards we have made for us current are Immersed Gold treated because we have been hand soldering and needed flat finish that would solder ok without tarnishing too quickly. I will take a look at the link you provided and follow up on some of the paste suggestions. Long shelf life would be great because we will usually make small batches and there will 1-2 weeks or more between our batches. We purchased the Stencil paste machine, Pick n Place and reflow oven mainly for pre-production runs (we have contractors that do larger runs externally) and for slower moving product lines that do not warrant large batches but we want to have stock to minimise lead times.

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Help with resources for SMT assembly | 1 October, 2015

Happy to help please do not hesitate to contact us we will send one of our Engineers in if need be. We also do a Solder Paste heat stable to 50C for non refrigerated use. BLT Circuit Services Ltd

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Help with resources for SMT assembly | 24 October, 2015

With regards to PCB surface finish I would recommend Electroless Nickel Immersion Gold (ENIG) because of the long shelf life, tarnish resistance, RoHS-compliance, and easy soldering compared to other surface finishes.

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