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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


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SMT vs TH | 2 March, 2011

Ok Guys I need help in justification of Converting TH boards to SMT. We do quite a bit of I/O controllers using sockets and chips, and our biggest defect issues are bad chips.

I am preaching to convert these boards over to SMT, however my designers are in the old school mind set.

I want to know your thoughts on:

1.Cost Comparison ( reducing processes/setups and TH and part costs) 2.Reliability and life increase of products. 3.Quality statements in general. 4.Any other attributes that you can think of.

Thanks Rich

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SMT vs TH | 5 March, 2011

We use both technologies and each comes with a mixed bag. What is the driving force behind your desire to convert? Is it just bad chips or something else? It sounds like you are having quality issues with your vendor and you would be good to address that issue first. That said, if you are purchasing parts out of the back of someones van (gray market), then I will assume some of the parts you are using are obsolete (and are just outright defective). If that's the case, convincing management shouldn't be to hard if they want to stay in business. They would have to redesign the pth product anyway so you might as well convert over to SMT. Cost will always be a concern, so you may want to see if they would be open to having a contract manufacturer build the boards for you.

Convincing management for the need for change can sometimes be daunting but it will come when it reflects on the bottom line. There are many advantages to going with SMT that I am sure you are aware. A smaller footprint being the biggest advantage. Is your company still designing new products with PTH technology? It may be they just don't want to spend the money on a new line. We converted out of necessity. PTH parts are getting harder to find, and when you do find them, especially the older parts, you pay tooth and nail for it. So many of your SMT parts will be cheaper. I don't know anything about your PTH line, but setup, depending on what system you are using can be a disadvantage with SMT. Our setup ranges from 2-4 hours per changeover. We don't have any change over time on our PTH line. Mainly because there are enough slots available for the components we use. What we loose in setup time we gain in speed. SMT is much more accurate in placing parts and much faster. Our SMT can place 20K/hour compared with 3-4K for our PTH. Mostly, when you convert or design new products using SMT, the product will have greater longevity than using PTH(Be careful, though, even SMT has many components that are at end-of-life). You will have more options for cross-referencing parts as well. SMT components are more reliable simply because they are newer. We have purchased many PTH parts that supposedly were brand new but didn't work per the spec sheet (counterfeiting could be an issue, but I cannot confirm this and have no personal experience with it).

With SMT, you get new problems. Solderability can sometimes be an issue. You get lifted leads which can be difficult to detect; therefore, if you can convince management to purchase an SMT line, have them throw in a good AOI system as well. It is well worth the money and will reduce rework and decrease repair time. Tombstoning is another issue you will see with SMT as well as insufficient solder. So there are many new defects thrown into the pot when you convert to SMT. But the conversion is well worth the trouble. But your company will have to decide what's best for themselves. In order for companies to be competitive, they have to invest in capital. That's a fact.

To sum up: 1)The speed of the AOIs should be a major selling point to management. There are much faster system out there than what we use. 2)Parts availability is another. Conversion out of necessity. 3)A smaller footprint should be a good point. Who doesn't want a more compact product that uses less power? 4)The added reliability of SMT components.

Good luck!


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SMT vs TH | 7 March, 2011


Thanks for the response. I agree with all of your comments, and actually we have SMT capability now. I also worked previously for a company for 20 years where we done primarily SMT and through the years phased out as much TH as possible, especially where the dip parts were concerned. Unfortunately I can't get to the supporting defect data that I was used to seeing on a daily basis. As you said, I think the amount of RMA boards we are getting back now is starting to warrant questions in our design and technology. In my opinion we are behind the times with our designs and have always had rather high ratios of returns. Even boards that are built for us have high return rates which a product of technology. We socket as much as 60 chips on one board. Makes since to me to surface mount these regardless of ease of replacement.

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SMT vs TH | 7 March, 2011

Now I have a clearer picture of your operation. It seems your company does not want to incur the cost of board redesign, and I thought it was the initial investment of the capital equipment that had them scared. You stated, "Unfortunately I can't get to the supporting defect data that I was used to seeing on a daily basis." You say you don't have failure data? Why not? What sort of data collection are you doing? I don't know that you can make a sound decision that going to SMT will fix your problems. It probably will, but your issue is masked right now because of your lack of data. You have to collect the data first to find out what the underlying problem with these boards are.

You need to find out why the boards are failing. Is it the parts, the sockets, or some other issue? It may be that it has nothing to do with the older PTH parts and you could save your company a lot of money by fixing the issue with the PTH boards. If it is the parts, that should be argument enough that conversion is warranted. However, if its not, conversion, at this point may not be. How is your parts sourcing for these PTH components? Is there plenty of supply?

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SMT vs TH | 7 March, 2011

I have been working on collecting data all day today. We are a OEM so our RMA and QA system is tied together. I have taken this data and broken it down by part type and individual boards. We had 264 (defects/rma returns) of that, 88 were NO Faults. Of the 176 actual defects/repairs entered, 147 were chip failures. The problem here is the guys doing the entries are not detailed enough. The highest defect part is a OPTO ISOLATOR 4ch 16 pin that is put in at DIP machine. I have 30 products that are SMT but low volume. Of the 2500 to 3000 SMT boards we have built this year I have no recorded RMA entries or defects during testing.

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SMT vs TH | 25 March, 2011

Has anyone found out why you are having so many optos fail in the field? It could be the design or possibly the customers application that is damaging this device (In which case, it may still be the design. Perhaps it's not robust enough.). Are these optos open-collector? What is the typical application? What type of load do they drive? Are you sure these devices are defective, or are they getting damaged in the field?

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SMT vs TH | 6 April, 2011


Appreciated the efforts put in.

Many Thanks, David.

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