Re: Discoloring of Soldermask and silkscreen

Netters,

When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong?

1. Kester 293 no clean 2. 2.1 C/s for 30s to 150 C 3. .5 - .7 C/s for 60s to 185 C 4. 1.5 C/s until 210 C for 30s

I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow.

PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings

PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol".

This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem.

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| Netters, | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | 1. Kester 293 no clean | 2. 2.1 C/s for 30s to 150 C | 3. .5 - .7 C/s for 60s to 185 C | 4. 1.5 C/s until 210 C for 30s | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | | | Tom, I would go for a vendor problem here, If it is only happening on this PCB. I take it the joints look nice and shiny, no discolouring on them ?

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| | Netters, | | | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | | | 1. Kester 293 no clean | | 2. 2.1 C/s for 30s to 150 C | | 3. .5 - .7 C/s for 60s to 185 C | | 4. 1.5 C/s until 210 C for 30s | | | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | | | | | | Tom, | I would go for a vendor problem here, If it is only happening on this PCB. I take it the joints look nice and shiny, no discolouring on them ? | |

I have some components that are not exhibitting wetting, like there is not enough heat. The SMT can Caps (lytics) and SMt crystals do not show good wetting (solderbility has been addressed), just does'n look like enough heat. But if I go for higher reflow "I might have some good toasted looking PCB's". I' talked to vendor, have sent a couple PCB's to him, pre-reflow and after, contacted the soldermask silkscreen vendor ( about 5 miles from each other, "dont know if good or bad").

Thanks

Tom B.

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| | | Netters, | | | | | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | | | | | 1. Kester 293 no clean | | | 2. 2.1 C/s for 30s to 150 C | | | 3. .5 - .7 C/s for 60s to 185 C | | | 4. 1.5 C/s until 210 C for 30s | | | | | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | | | | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | | | | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | | | | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | | | | | | | | | Tom, | | I would go for a vendor problem here, If it is only happening on this PCB. I take it the joints look nice and shiny, no discolouring on them ? | | | | | | | I have some components that are not exhibitting wetting, like there is not enough heat. The SMT can Caps (lytics) and SMt crystals do not show good wetting (solderbility has been addressed), just does'n look like enough heat. But if I go for higher reflow "I might have some good toasted looking PCB's". | I' talked to vendor, have sent a couple PCB's to him, pre-reflow and after, contacted the soldermask silkscreen vendor ( about 5 miles from each other, "dont know if good or bad"). | | Thanks | | Tom B. | Hey Tom, I had the same problem with some boards here. I solved it by going with a lower temp and a longer soak. but I just assumed they where cheap boards. If your vendor has been giving you problem free boards and this one just didn't make the grade, maybe they sent it out? Does the board even look the same as the ones they have been giving you?........Jeff

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| Netters, | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | 1. Kester 293 no clean | 2. 2.1 C/s for 30s to 150 C | 3. .5 - .7 C/s for 60s to 185 C | 4. 1.5 C/s until 210 C for 30s | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | | |

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| Netters, | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | 1. Kester 293 no clean | 2. 2.1 C/s for 30s to 150 C | 3. .5 - .7 C/s for 60s to 185 C | 4. 1.5 C/s until 210 C for 30s | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | Tom: Two things:

1 I doesn't take much (15-20C) to make HiSol silk screen ink go tan 2 It takes a lot to discolor SR1000. That is mean stuff.

It makes want to ask:

1 What makes you so sure about your temps 2 How well are the temps controlled?

Beyond that, SR1000 is a really old wave solder liquid solder mask. Do you wonder if you should be using something more up tech for SMT boards?

TTYL

Dave F

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| Netters, | | When I reflow a PCB there is a discoloration of silkscreen and mask. It appears if Profile is too hot! But I dont think so, maybe I'm wrong? | | 1. Kester 293 no clean | 2. 2.1 C/s for 30s to 150 C | 3. .5 - .7 C/s for 60s to 185 C | 4. 1.5 C/s until 210 C for 30s | | I preheat to 150 for about 30s, then soak for 60s ramping to 185, then spike to 210 c for reflow. | | PCB is supossed to be 94v-2 .062 with 1oz copper. There is no 94V symbol, I have contacted UL for other acceptable markings | | PCB has "Hi SOL" SR or SL 1000 thermal cure epoxy soldermask (Vendor info) Silkscreen is two part epoxy "Hi Sol". | | This is only PCB I have seen do this, it is a new PCB to us. We have used this vendor in the past, no problems that I can think off. I can take another PCB about same or less run thru oven no problem. | I'm with Dave's line of thinking on this one. Sure sounds like tunnel stability issues. It's been lotsa years since I fought the ole amber silkscreen......back when IR lamp and radiant panel technology was the rage in ovens.......So I gotta ask......are you using convection technology for reflow? Did we miss the obvious?

My bet is that you've got an older technology in your oven, and you are approaching glass transition stage. I've also seen this occur if a board house runs the boards BACK through solder leveling a second time........as a "rework" mode.

So.....if you DON'T have convection, beg, borrow, or steal the funding to get it. It will save you many headaches! And I'd be very happy to recommend a brand and back it up with test results from a good, solid test for efficiency of thermal transfer and delta T..........just ask (privately).

Scott Cook scook@nettally.com

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