2007: the year of HDI? A reader survey reveals 2007 will be the year microvias and embedded passives make their mark.

What bare board technologies are expected to gain ground during the next 12 to 18 months? In a first-of-its-kind survey of some 5,100 designers and assemblers undertaken by UP Media Group in late October, we learned that 2007 will be the year when 0201s and embedded passives become mainstream and Pb-free processing provides a major boost to high Tg laminates.

The survey was conducted Oct. 24 to Nov. 7, 2006. In all, 5,118 North American subscribers of Printed Circuit Design & Manufacture or CIRCUITS ASSEMBLY were surveyed, with 244 responding, a response rate of 4.8%. Respondents were provided a copy of the results, but no other incentive. The survey targeted PCB designers and manufacturing engineers; fabricators were not polled because they tend to be technology implementers, not drivers.

The results establish certain trends in board technology, including:

* Laminates.

* Final finishes.

* Soldermask.

* Lines and spaces.

* Layer counts.

* Components and packaging.

* Advanced technology needs.

* Fabricator yields and common defects.

They also reveal procurement trends, including from whom boards are bought and current and projected value of board buys.

Of those surveyed, 79.5% identified their company as an OEM, 8.2% as an electronics manufacturing services provider and 7.4% as a design services bureau. Most of those who specified "Other" were with R & D labs, engineering centers or consultants.

Of the respondents, 68.9% were printed circuit or systems packaging designers, 24.2% were process or manufacturing engineers and 2% were in procurement. More than 22% said the primary end-product designed at their location was instrumentation or industrial electronics, followed by defense, military or aerospace (19.3%); communications systems or equipment (17.2%); automotive (8.6%); computers, data processing equipment or computer peripherals (8.2%); consumer (5.7%) and medical (4.9%).

Laminate Trends

The majority of respondents expect to continue to use rigid materials (Table 1). The trend is toward higher Tg laminates (Table 2), probably because of increased use of Pb-free solder alloys, which have higher melting points than their SnPb counterparts.

Design Trends

For the time being, lines and spaces of 0.004" to 0.006" remain predominant, while 0.003" lines and spaces inch toward mainstream use (Table 3). No major changes in foil thickness are anticipated (Table 4). Layer counts are rising incrementally, but single- and especially double-sided boards are still common (Table 5). Perhaps the next data point explains why: More than half of those responding said they expect to use microvias in their designs within 18 months, up from 34% currently (Table 6). Embedded passive use will jump markedly as well.

Finish Trends

ENIG will remain the preferred final finish among North American companies, the survey found. Pb-free hot air leveling will supplant HASL during the next 18 months, again thanks to implementation of Pb-free designs (Table 7). Liquid photoimageable will remain the dominant soldermask choice, with 81.6% of respondents indicating use in 12 to 18 months. Use of dry film (17.6%) and screen-defined masks (13.1%) will remain constant.

Component Trends

The minimum size of passives will shrink appreciably in the coming months. While 0201s have for years been mainstream in cellphones and other devices such as GPS systems, engineers expect their use to jump during the next year (Table 8). And the smallest available package style--01005--will begin to come into play. In all, nearly 31% of respondents predict they will use 0201 or smaller devices, double the current mark.

Board Quality

While most respondents indicated a greater than 95% acceptance rate for bare PCBs from their primary supplier, 13.5% pegged the rate at between 70 and 90% (Table 9). The most common defects reported on bare PCBs centered on the laminate, followed by solderability and plating (Table 10).

This may be remembered as the year HDI finally joined the ranks of conventional technology in North America. If embedded passive use rises in line with what respondents indicated, that too will boost HDI use, as the two technologies go hand in hand. The reverberation of Pb-free will show up across many new product lines as well.

Mike Buetow is editor-in-chief of CIRCUITS ASSEMBLY.

Table 1. Laminates Typically Specified

                                              Today  12-18 Mos.

Rigid (FR-4)                                  87.3%  84.8%
Standard multilayer                           67.2%  65.2%
CEM                                            8.6%   9.0%
High-performance multilayer                   50.4%  58.2%
Paper                                          2.0%   1.6%
Flexible (polyimide or polyester)             28.7%  30.3%
Rigid-flex (including multilayer rigid-flex)  25.0%  27.0%
Don't know                                     0.8%   2.5%

Respondents were asked to check all that apply.

Table 2. Typical Laminate Tg

                                   Today  12-18 Mos.

Tg <150[degrees]C                  14.8%   9.0%
Tg 150[degrees]C to 170[degrees]C  33.6%  22.5%
Tg 170[degrees]C to 200[degrees]C  27.9%  40.2%
Tg >200[degrees]C                   9.0%  11.5%
Don't know                         14.8%  16.8%

Respondents were asked to check all that apply.

Table 3. Conductor Widths and Spacings

                           Today  12-18 Mos.

0.001/0.001"                2.9%   3.3%
0.002/0.002"                4.9%   9.4%
0.003/0.003"               18.4%  29.9%
0.004/0.004"-0.006/0.006"  57.0%  60.7%
0.006/0.006"-0.008/0.008"  50.0%  46.3%
0.008/0.008" or above      45.1%  40.6%
Don't know                  4.5%   6.6%

Respondents were asked to check all that apply.

Table 4. Copper Foil Thicknesses

                      Today  12-18 Mos.

Semi-additive copper   1.2%   3.3%
1/8 oz.                5.7%   6.1%
1/4 oz.               14.3%  18.9%
3/8 oz.               10.7%  13.1%
1/2 oz.               70.5%  70.1%
1 oz.                 69.3%  66.8%
1 to 5 oz.            43.9%  43.4%
More than 5 oz.        4.1%   6.1%
Don't know             7.4%   9.4%

Table 5. Typical Layer Counts

                     Today  12-18 Mos.

Single-sided         20.9%  20.1%
Double-sided         59.8%  57.4%
4 to 6 layers        75.0%  74.2%
8 to 10 layers       57.4%  61.1%
12 to 18 layers      38.5%  44.3%
18 to 24 layers      17.2%  21.3%
More than 24 layers   8.6%   9.8%
Don't know            0%     1.6%

Respondents were asked to check all that apply.

Table 6. Advanced Fabrication Techniques

                                     Today  12-18 Mos.

Chip carriers (single and multiple)  21.3%  21.7%
Microvias (0.005 or less)            34.0%  52.5%
Blind vias (any type)                47.5%  56.6%
Buried vias (filled and unfilled)    40.6%  48.4%
Impedance-controlled boards          66.8%  70.9%
Backdrilling                         13.5%  17.6%
Embedded passives                    11.1%  24.6%
None of the above                    19.3%  13.1%

Respondents were asked to check all that apply.

Table 7. PCB Metallic Finishes

                       Today  12-18 Mos.

Copper only (OSP)      22.5%  23.0%
HASL                   55.3%  40.6%
Pb-free HASL           23.0%  37.3%
SnPb plate and reflow  18.9%  12.3%
Immerson tin           18.0%  18.9%
SnNi                    7.0%   6.1%
Electroplated NiAu     29.5%  31.6%
ENIG                   59.0%  59.4%
Immerson silver        27.5%  34.4%
Other                   0.8%   2.0%
Don't know              1.2%   4.1%

Respondents were asked to check all that apply.

Table 8. Minimum Passive Size

            Today  12-18 Mos.

01005        0%     2.9%
0201        15.2%  27.9%
0402        56.1%  51.2%
0603        23.4%  10.2%
0804         1.6%   1.6%
1206         1.6%   1.6%
Don't know   2.0%   4.5%

Respondents were asked to check all that apply.

Table 10. Common Bare Board Defects

Laminate (pits, dents, bow/twist, delamination, measling,          38.9%
  registration)
Solderability                                                      31.6%
Plating                                                            28.7%
Surface finishes (poor coverage, etc.)                             26.2%
Electrical (crosstalk, impedance, etc.)                            25.0%
Drilling (burrs, nailheading, misregistration, pad tearout, wedge  20.5%
  voids, pink ring)
Cleanliness                                                        18.9%
Legend/screen (misprints, etc.)                                    15.6%
Missing conductors/pads                                             7.8%

Respondents were asked to check all that apply.

Table 9. Bare PCB Acceptance Rate

>95%    64.3%
90-95%  21.3%
80-90%  11.5%
70-80%   2.0%
60-70%   0.0%
<60%     0.8%