Tag Archives: Components

And Another Footprint Thing

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 When you are creating a footprint in your favorite CAD program, or reusing someone else’s footprint, double check the zero orientation. This post discusses the IPC-7351 specified zero rotation orientation.

This picture on the left shows a library component with the improper zero rotation orientation. Your centroid file will never be correct if you start from the wrong point.

IPC-7351 states that the LED should be oriented horizontally and the cathode (pin 1) should be to the left. Obviously, vertical and cathode up is not the same thing as horizontal and cathode left. If it’s obvious, why do I feel the need to state it? I don’t know. I just do.

Duane Benson
Red is gray and Yellow white
But IPC decides which is right

http://blog.screamingcircuits.com/

Rain, Rain, Go Away

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It’s almost June here in the Pacific Northwest. At least, that’s what the calendar says. I’m not sure I believe it at the moment. The weather is acting more like October. It’s a bit warmer than January, but every bit as wet. That pretty much equals October. We’ll just call it Junetober.

And what does Junetober have to do with electronic assembly?

MSD logo Moisture. That’s what it has to do with electronics assembly. Most of the parts running around in the world today have some level of moisture sensitivity. Despite my lament of the rain here, you have to consider component moisture no matter what your climate may be.

Looking at IPC-M-109, you can see the there are sensitivity levels MSL-1 though MSL-6. There are actually eight levels: 2A and 5A make up the extra two. If you’ve got an MSL-1 part, you really don’t have to worry about. I wouldn’t store it in your fish bowl, but the standard says you don’t have to bake it. Up at MSL-6, you have to bake the parts before use no matter what.

When you buy moisture-sensitive components, they should come in a moisture barrier antistatic bag with an indicator card and a little baggy of moisture absorbing desiccant. The best approach with these components is to leave them in the original, unopened bag. We’ll use what we need and properly seal up the rest just the way IPC-M-109 wants us to.

If you do need to open the bag and ship parts to us without the moisture protection, we may need to bake them for a while to make sure they are properly dried out before putting them in the reflow oven.

Duane Benson
Gore-Tex is a registered trademark of W. L. Gore & Associates.
http://blog.screamingcircuits.com/

Sales Up, Profits Down

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Another round of EMS quarterly reports came out today, as LaBarge and SMTC provided their numbers. Now that the bulk of the major EMS companies have reported, the picture is pretty clear that first quarter revenues were up fairly broadly but profits took a hit.

This is unfortunate, of course, because the margin-sensitive EMS industry relies on leveraging higher sales to drive incremental profit gains.

Based on the consensus forecasts, expect second-quarter revenues to be generally flat, with pressure on margins because of higher component costs due to supply constraints.

Time to Panic?

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Anecdotal reports indicate some manufacturers are purchasing larger-than-needed amounts of raw materials and certain components out of concern for supply availability in coming months. This is all tied to the shortages brought on by the earthquake and tsunami in Japan.

In the near-term, I expect analysts will be a bit confused as to what’s real demand and what’s over-ordering. Something to watch.

 

Drip. Drip. Drip. Drip. Drip …

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Okay, water doesn’t have to actually be dripping down on to your parts to be a problem. I don’t know if you’ve heard or not, but water also comes in vapor form. Weird. I wonder if there’s a way to harness water in that vapor stage and do something useful with it. Hmmm. Ponder material for another day.

Here is something not so useful about vaporous water: It can get into your parts and make them unhappy. I was recently asked about opening and resealing moisture barrier packages for moisture-sensitive parts. This old post has a link to the IPC and Jedec standards document (J-STD-033B.1) covering this subject. It can be a complicated subject and the document is worth the read.

In sort, the best thing to do is just leave the parts sealed in their original moisture barrier packaging. If that’s not practical, look at the MSD classification. There are eight levels with one being least sensitive and six being most. (Levels are 1, 2, 2A, 3, 4, 5, 5A and 6). Most parts seem to be level 3, which can be open and exposed for a cumulative time of 168 hr. The actual safe time may vary based on your local humidity.

If you want to open and reseal, you’ll need the humidity indicator card that came with the parts, desiccant and a thermal sealing gizmo. Open the package, take out the parts you need, put the remainders, desiccant and card back in the package and reseal it. Sealing it with tape won’t do the trick. Then you would count the time that the components were in the open air toward the cumulative open time.

If there’s any doubt, just let the assembly house know that the parts need to be baked. It will probably add some time to your job, but it’s better to add a bit of time than have bad parts.

Duane Benson
Add walnuts and chocolate chips.
Two

http://blog.screamingcircuits.com/

Hello… Any Good Part Shipping Ideas?

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Ever have one of those situations where there really aren’t any good answers? There may be right answers, but not necessarily any that fit well to the specific situation or are all that convenient.

The question at hand relates to packaging and shipping small quantities of large ICs to your prototype house. If you buy them in small quantities, go ahead and use that packaging to ship to Screaming Circuits. That’s not a problem. The problem (and this question) comes when you need to purchase a bunch of them but only need to use a few at a time. This is primarily an issue for parts that come in trays.

Let’s say you have a 23 x 23mm BGA or QFP that came in a tray with 60 parts. You need to ship five of the parts for an assembly order at Screaming Circuits. We tell you not to ship them loose. You don’t want to risk in-transit loss or damage to all 60 parts by shipping the full tray. What do you do?

For leadless parts like BGAs, LGAs and QFNs, you can carefully pack each one in a small individual anti-static bag and then wrap them in bubble wrap. You can’t do that with leaded parts like QFPs. Don’t do it. Bent leads don’t solder well. And, don’t put more than one BGA in an antic-static bag. Missing solder balls won’t solder either.

For all types of chips, you could take a band saw to a spare empty tray and cut it down to the size you need. Or, better yet, you can find someone that sells JEDEC Matrix IC Trays and see if they have any that meet your size and capacity requirements. www.topline.tv or www.practicalcomponents.com are good places to start. That won’t help much if it’s noon on Tuesday and you need to make a shipping deadline of 3 pm. But it will likely help for future projects.

If you do choose to send in your full tray, we will treat all of the parts with care, bake if needed, properly reseal and pack them for the return trip to you.

Duane Benson
Three

http://blog.screamingcircuits.com/

Narcissistic Parts

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Maybe not completely narcissistic, but at least self-centered.  Or, self-centering. Okay, are you lost now? Am I making any sense at  all? Well, I’m going to say that it doesn’t matter, because the  world-revolves around me.

But what I am talking about is parts that will more or less center themselves during the reflow process. Some parts like BGAs and QFNs tend  to follow the surface tension of the melted solder and tweak themselves  into a more centered position on the land. That’s a good thing.

It’s not always a good thing though. Sometimes that same surface  tension action can work against you. Take this TO-263 (pictured). When it was placed on the land, before reflow, the leads were centered  right in their pads like they should be. The big land for the thermal  pad is set up a little too high though and once melted, the surface tension from the big thermal pad sucked the part up, nearly dragging it  off of the lands for the leads. Bummer days. Here’s another example.

You probably shouldn’t leave the part like this, so here’s a few suggestions.

You could make the thermal pad smaller so that when the metal tab of  the part is centered, the leads will be, too. Cooling needs might dictate  that you don’t reduce the size of the pad, though. If that’s the case,  you could make the bad bigger by extending it down toward the leads, again so the leads will be centered when the body of the part is. You could also mask off the top part of the pad, or put a thin strip of mask  as a solder dam. What you’re doing is making sure that if and when surface tension moves the part, the leads will end up where they are supposed to.

<em>Duane Benson
It is all about me, you know</em>

http://blog.screamingcircuits.com

Presience, or False Alarm?

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“2010 becoming very reminiscent of 2000, where poor inventory control, and concern over long waiting times for leading-edge equipment spelled disaster, and we ended the year with $10 billion in excess IC capacity and a shattered equipment industry that took years to claw out of the red and never fully recovered until this year.”

That’s the comment from the president of The Information Network, a US-based research firm. Is he right?

I tend to disagree. I think the inventory levels are still well in line with historical norms as baselined over the past seven years and well below the glut in 2000-01. Yes, a few big OEMs have invested large sums (a reported $100 million for Cisco) to ensure stock of certain parts, but for almost everyone else inventory is scarce. Lead times for some parts are out to 20 weeks — but Top Tier EMS companies have been upfront with Wall Street about the issue and no one can has been able to cite to me orders lost from an inability to get parts.

Instead, what’s happening is programs are getting pushed out. It doesn’t make anyone happy, but it’s far better than the alternative scenario of excessive inventories and battles over who will pay for them. That itself sets 2010 apart from 2000, in my opinion.

All supply chains have an inevitable tension. Far better for it to be taut than loose.

Ambiguous PCB Markings

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Here’s a little issue we run into now and then. Which reference designator goes with which part? Quick. I need to know. Now. Now. Now!

It’s less of an issue with SMT parts because we machine place them and use your centroid file to do the programming. Still though, It’s always good to have things marked clearly in case rework is needed and for visual inspection.

For through-hole, though, it is definitely an issue because a real human being is putting the parts in and the visual markings are the programming for the human type person.

For best results, take a little extra time and make sure all of your ref designators are clearly associated with the correct part. It’s also always a good idea, when possible, to have all the designators in the same position relative to their part. Consistency is a good thing here. Consistency is a good thing with mashed potatoes too. Who likes lumpy mashed potatoes?

Duane Benson
You say poe-ta-toe, I say ugly brown tuber

http://blog.screamingcircuits.com/

That Dreaded ‘Allocation’ Word

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Here at the old Screaming Circuits homestead, we have a strict policy about parts substitution. We won’t do it unless you have approved the sub. If you ask us, we’ll look around for something close, but we’ll still get your approval before using the substitute part. No big deal: We always do it that way and we’ll keep doing it that way.

The reason I bring this up has to do with the blasted economy. Rumor has it that the industry is starting to heat back up a bit. That’s pretty cool, except that some of those parts suppliers that cut back this time last year are still in cut-back mode. We’re starting to see parts on allocation and with annoyingly long lead-times.

Interestingly, most of the long lead-times seem to be with passives at this point. Actives may end up that way too, but for now, it’s mostly in resistors and caps.

So, what do you do about it? Well, if you spec’ed the parts out a couple of weeks ago when starting the design, you might want to drop on over to Digi-Key (or equivalent) and check to see if the parts you specified are still available. If not, find a sub before sending it off for assembly. It helps for you to do this even if we’re buying the parts for you. If we can’t find what’s on your BoM, we’ll look around for a couple of options, but if you’ve already found a replacement that works with your design, that will save some time and back and forth email or phone call steps. It also prevents a last minute surprise and keeps you on top of the planning.

Anyone else out there seeing allocation and lead-time problems?

Duane Benson

http://blog.screamingcircuits.com/