New to surface mount PCB's
New to surface mount PCB's
(OP)
Hi,
I've done thru-hole PCB design for 25 years and am now
going to finally get to layout a surface mount design
for the 1st time. I'm looking for good reference data
on surface mount (books, magazine articles, etc.) and
any advice I can get. Thanks.
I've done thru-hole PCB design for 25 years and am now
going to finally get to layout a surface mount design
for the 1st time. I'm looking for good reference data
on surface mount (books, magazine articles, etc.) and
any advice I can get. Thanks.
Steve Smith
Product Engineer
Staco Energy Products Co.
www.stacoenergy.com





RE: New to surface mount PCB's
http://www.smtmag.com
You may qualify for the free subscription. There is also more info available about SMT at that web site.
RE: New to surface mount PCB's
Some of the best reference data for pad sizes and clearances is to be found in the manufacturer data sheets for the parts specified in your design(s). These often have layout cell footprints typical of the packages surface mount parts come in.
Some general tips...
1. Advantage: Surface mount parts generally allow more routing flexibility in the PCB sandwich layers. Use it.
2. At some point, a surface mount connections may have to via to another layer.
3. Disadvantage: Surface mount parts are frequently smaller than thru-hole ones, with pad/trace size decreasing as circuit density increases. Wave soldering or oven soldering during assembly is required in most design cases. The design should be correct the first time, because rework is usually not feasible.
3A. TIP: Insert test points on key surface mount signals, routing them to some place accessible on the PCB.
4. The densest surface mount IC package today is the Ball Grid Array. Be extra careful on via size, pad diameter and via-pad clearances.
5. Do not place surface mount parts in areas where the PCB flexes. They can lose cohesion after enough flexing.
Enjoy.
Warpdrive
RE: New to surface mount PCB's
I found the both informative.
Steve Smith
Product Engineer
Staco Energy Products Co.
www.stacoenergy.com
RE: New to surface mount PCB's
stelleb
RE: New to surface mount PCB's
I'm showing my ignorance here, but what is JTAG?
Steve Smith
Product Engineer
Staco Energy Products Co.
www.stacoenergy.com
RE: New to surface mount PCB's
good luck,
stelleb
RE: New to surface mount PCB's
Thanks, you deserve a gold (well purple) star for this tidbit.
Regards,
Steve Smith
Product Engineer
Staco Energy Products Co.
www.stacoenergy.com
RE: New to surface mount PCB's
Thanks to stelleb for the insights on JTAG boundary scan testing. However, be advised that while JTAG boundary scan test equipment is highly useful it can become pricey. I'm receiving quotes starting at $15K and going up for the JTAG BST system I'm seeking to implement.
Stelleb is also correct about test points consuming PCB space. I recommended test points because my most common customer's field technicians do not wish to be burdened with reading and deciphering 100-800 bit wide registers. That exercise is reserved for the engineers and production, T&E technicians. The trade off comes with determining how many test points are necessary and whether or not a JTAG scan tester is available. Ultimately, whether test points are used depends on any long term servicing requirements.
Where JTAG testing excels is accessing signals that are buried inside a chip, or are otherwise inaccessible to probing on the PCB. Stelleb describes this nicely.
If JTAG testing is not feasible, one "de facto" method of placing test points is using the vias that PCB tools automatically set during trace routing. Though this tends to scatter the "test points" across the PCB, it still makes key signals accessible without significant PCB real estate penalty. A little silkscreen can label each key signal at the via/test point.
Glad we could help.
-- Warpdrive
RE: New to surface mount PCB's
RE: New to surface mount PCB's
One other quirk that doesn't show up in most reference material is the care you have to take with any surface mount connectors that might be expected to take an external vibration or cantilever load. A row of header pins, for example, will have enough mass that they can't be effectively soldered in the same pass as the much smaller components on the board. Often these larger parts must be hand-soldered after the fact or you'll get a cold joint and they'll break off easily when being assembled to their mating connector (or worse, after installation to a vibrating piece of equipment).
Best of luck with your work!
Kindest regards to all,
Old Dave