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36 SMT Magazine • June 2016 Las Marias: So what innovations in solder paste dispensing or jetting are happening to help customers address that issue? Gu: Actually, we are using needle dispensing instead of jetting, but I know there are maybe one or two vendors here that are using solder jetting. Of course, solder jetting is much faster than solder-based needle dispensing. But you know, the key limitation of solder-based jet- ting is that we cannot use many types of solder pastes. Solder pastes have many types—type 1 through type 6. The smaller the solder particle, the more expensive the paste. For instance, a type 6 solder paste is maybe 10 or 15 times more expensive than type 5 solder paste. For solder paste jetting, maybe we can only use type 5 or type 6. But for our needle dispensing, we can use everything from type 1 to type 6—this is one advantage of needle dispensing. Las Marias: Why do you think most manufac- turers still prefer using solder paste printing? Gu: Solder paste printing is much faster than solder paste jetting or dispensing. It is also much stabler because it is a one-step process. But for very complicated boards, with very small or very tight accuracy levels, you will need solder paste dispensing. Las Marias: Can you tell me some of the fac- tors I should consider when selecting a solder paste dispensing system to use? Gu: We are using needle dispenser, so I will speak from that perspective. In needle dispens- ing, we use air pressure to press the solder paste into what we call a package, just like a tank. The solder paste will be soft for a little while. We use a kind of motor to push the solder paste through the needle. So the needle size selection is very important because there's always some filler inside of each solder paste, and it's differ- ent for each type. For example, type 1 will have the bigger filler size, and type 6 will have the smaller filler size. So for example, if you want use type 6 solder paste, the filler size may be 20 micrometers. Then the inner diameter of the needle must be seven times bigger than the filler size—so 140 microns. This is a rule. Otherwise, you will encounter problems. Another thing, you need to control the solder paste flow and always keep it stable. There are many factors, like air pressure, mo- tor speed, and dispenser head, you have to control the flow rate to make the dispense line very stable. Las Marias: Eric, what can you about the fu- ture of your industry? Gu: Technically, I think the dispense qual- ity will become more and more strict and more complicated. Maybe it will require much small- er dispense dots, solder paste dots, or line. Right now we can dispense around 215 microns. Maybe later we will be down to 100 microns. So this is a very big challenge. Another thing is the speed, the UPH. That's why more and more vendors are developing solder paste jetting, but you have to balance the cost and the UPH. If you are using solder paste jetting, of course, the cost is maybe three or four times higher. Also, for the material, solder paste jetting can only use type 5 or type 6 pastes; so another challenge for the future is how to start using type 2, type 3, and type 4 solder pastes in jetting. Las Marias: Eric, thank you very much for your time. Gu: Thank you. SMT SOLDER PASTE DISPENSING: BREAKING THE LIMITS OF PRINTING

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