In This Issue

 Standard Flex Materials
 By Dale Baird

 Rigid-Flex Drawing Reqt's.
 By Marc Strickland

 Lenthor Links

 Presidents Letter
 Words From Mark Lencioni

 Virtual Contacts
 Contact Our Key Employees

 Design Guide
 Download Our Design Guide

 Resources

 Flexible Circuit Materials
 Information on Flex Materials

 Isola Materials
 Rigid Epoxy Material

 Hitachi Chemical Co.
 Rigid Polyimide Material

 IPC Home Page
 Industry Standards

 Newsletter Links

 http://www.lenthor.com
 Lenthor Website

 davidm@lenthor.com
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Are you starting to see material lead-times creeping out there again? The market has been improving and, because of the amount of plant closures throughout the United States, it doesn’t take a lot of recovery for material suppliers and fabricators to get back to capacity.

This month we are giving you a form that can and should be used as a template for completing your rigid-flex fabrication drawings. There may be a few new blanks for you to fill in that have been missing from your current standard drawings. By checking or using this form before sending your jobs out, less questions will need answering before engineering, tooling and manufacturing of your circuits can start.

Now back to the subject at hand, “using standard flex materials”. As material, chemical and component suppliers get busier, they normally like to make more and more of less and less variations of their products. This means that as you stray further from using these standard materials, lead-times can be longer, and sometimes they can be really, really long, as in the manufacturer stops making them completely. For this reason, I would like to recommend you attempt to design using the most standard materials whenever possible, assuming you’re not already doing that.

What are the standard flex materials? Okay, that all depends. For Lenthor Engineering, we stock a fairly broad range of base laminates and coverlay materials. It is safest to ask each of your flex suppliers the same question. In general, you will find that 1 will be a recurring number, i.e. 1 mil Kapton, 1 mil Adhesive and 1ounce Copper. Because of the higher density designs requiring finer line and space widths, ½ ounce Copper has become equally available but carries a small cost adder.

Another good guide to material availability can be found by studying pricing “U” curves. Flex laminate costs start out higher per square foot for thicker types, say 5 mils, and get lower for 3 mils, lower for 2 mils, until you reach 1 mil, then they start to go up again as the laminate gets thinner, like for ½ mil. The same “U” curve exists for varying Copper weights, Coverlay materials and Kapton stiffener materials. Materials at the lowest point in the “U” curve are most likely to be the most available.

So if you haven’t already finished your next flex circuit design, spend a few minutes with your supplier(s) to review their list of least expensive, most available materials. If you can incorporate them into your design, you’ll be able to sleep better at night knowing that getting a good supply of flex circuits is reasonably assured. And don’t forget to review the checklist below before you release your next order!

Dale Baird
V. P. Sales and Marketing
Lenthor Engineering LLC

Rigid-Flex Drawing Requirements

Drawing Notes:

1. The PCB shall be fabricated to IPC-6013, class (your requirement here) standards.
2. The PCB shall be constructed to meet a minimum flammability rating of V-0 (if required)
3. The rigid material shall be GFN per IPC-4101/24 (if using epoxy material)
4. The rigid material shall be GIN per IPC-4101/40 (if using polyimide material)
5. The flexible copper clad material shall be IPC-FC-241/11 (flexible adhesiveless copper clad dielectric material)
6. The covercoat material shall be per IPC-FC-232/1.
7. The maximum board thickness shall not exceed (your requirement here) and applies after all lamination and plating processes. This is measured over finished plated surfaces.
8. The thickness of acrylic adhesive through the rigid portion of the panel shall not exceed 10 % of the overall construction.
9. Pouch material may be used for ease of manufacturing and must be removed from the flexible portion of the board prior to shipping.
10. The flexible section thickness shall be (your requirement here, do not add this note if this thickness is not critical).
11. Minimum copper wall thickness of plated through holes to be (your requirement here) {.001" average is recommended} with a minimum annular ring of (your requirement here).
12. Apply green LPI soldermask (if required) over bare copper on both sides, in the rigid sections only, of the board. All exposed metal will be (your surface finish requirement here).
13. Silkscreen both sides of the board (if required) using white non-conductive epoxy ink.
14. Your marking and identification requirements here.
15. Your electrical test requirements here.
16. Your packaging and shipping requirements go here.

Additional Drawing Requirements:

1. A drill symbol chart is required. This chart depicts your finished hole sizes and associated hole size tolerances. A finished hole size of +/- .003" is typical.
2. A dimensional drawing is required. All critical dimensions must be noted and the rigid to flex interfaces (this is where the rigid material stops and the flexible material begin) must be defined. Typical outline tolerances are +/- .010". If a pallet or array is required a dimension view must be supplied for this as well.
3. 3) A board construction and layer order is also required. This should show which layers are rigid material and which layers are flexible material including copper weights. Here is a sample board construction and layering:


4. A drawing revision table is advised. Your company name, part number, current revision should be in the title block area of the drawing.

Marc Strickland
Process Engineering Manager
Lenthor Engineering LLC